zslz¡tr,

The ecological energetics of Pararlgq_ia zi-etzij¿na Sayce

(Crustacea.:Anostraca) in tl¡o sah.ne lakes in r^iestern

Victoria

by

R. Marchant B.Sc. (Hons.)

T,oology Department, University of Adelaide

Thesis for the Ph.D. degree,

November, 1976.

TA3I,E OF CONTENTS

CHAFTER 1 - Introducti.on

CHtrPTER2-Stuclyarea

Ptlyslcal and Chenj.cal features

Methods

, Resr¡lts and Discussfon

Biological features

CHAPTER 3 - PopuLa.tíon densíty of B¡-Zþ!4!4Methods

ResuLts

Discussion

CHAPTER, /r - Life history, growbh and production ofP. zj-et'ziana

Methods

ResuLts

(a) r,ite history

(b) nreeding bloLory

Di.scussÍon and. Production esti-nates

CHAPTER 5 - Respiration of !-*i@!ana.Methods

Resul-ts

Discusslon

CHAPTER 6 - Ðrerry content of lake sedirnents

Methods

ResuLts

Dlscussion

W".1

6

6

6

9

9

L6

L6

L9

22

25

25

26

26

34

38

5L

53

56

6l+

7¿ï

75

76

82

IABI,E OF CONTE¡I1S (conti¡ued)

CHAPTER 7 - Ingestlon a¡d. egestion þ P. zfetziana

Methoils

(a) Isotope erçerlnents

(u) faecal pellet production

Resu]"ts

(a) Isotope experinents

(U) tr'aecal pellet production

Discussion

CHAPTER I - Enerry budgets for Uþlglgg andconclusions

Introductlon anil Methods

Resr¡].ts

Dlscussion

REFERB$CES

aaaao

B.ggg&.

85

87

87

89

90

90

99

101

1L3

TL3

lJA

l_21

126

ABSTRACT

P" z.ietziana (Urtne shri:ap) r¡as studled for tuo years in tl¡o

shall-or¡ (-<f n), saline (=60 %') lates, Iake Cundare a¡d Pink læ.ke,

26 kffi. north of Colac, Victorla. fhere were narked fluctuations ln

sal-fnity in both lakes during this study, the hlghest sel'inÍ'bies

occurrÍrrg in sumner.

Quantitative sanpLes of P._zietzÍar-ra, r¡ere t¿ken monthly. These

showed that on most oecasíons the shrÍnp,'were contagiously rllstributed., Imost probably due to rrind generated currents. Despite stratlficatlon

L'

of the sanples, the confidence li-¡nits of the average population density

vere /+O-5O%. However, sanpling rras representative because stable trends

energed and varÍabllity vras not so great that signíficant differences

could not be detected.

Cohorts of the shrinp were disti-nguishable and a regression

established betl¡een length and dry treight" Thus growbh could be

calcr¡lated ancl then production by combining density and grorrbh data

1n Allen clrrveso General-Ly, there uere tuo or three generatlons each

year, but tj¡e of rec¡r:itnent was not predlctable. In aal cohorts

,there was more or less continuous nortali.ty whlch r¡as not due to salinity

or tenperature stress except in summer. Productj.on uas largely clue

to the death of small individuals and vas about ten times higher in

Pi¡k La.ke (11. I g f2 y"ut-l¡ than in Ï¿ke Crr.ndare (1.0 g, ,fz yuu"-l¡,

as l¡as the population density.

Respiratory rate was neasured by lncubating P. zietz:Lgua 1n situ in

B.0nDo bottles. Tests ín which the orygen decli-ne was monitored

continuously sholreC there lras no hand.ling effect and that respiraiory

rate was constant dorrn to 1,8-1.9 ag OZ 1-1, abou f 3O/" of the usual

initial concentration. fncubatlons over tu'enty*four hours denonstrated

,L

there uas no diurnal variation in orygen consr:rnption. Â nultiple

regression analysis of the data ÍndÍcated that' 90% of the variance

i-n resplratory rate was accounted for by changes in salinit¡ 0/"),

tenperature (7/,) and. dry weight (BO/"). From the regression equatlon

and data on popuJ-atlon density, populati-on respiration Ìras calculated.:

9I86tr.5 ng oz.-2 y"*-1 in Pint arß, I?36'7.5 mB orf' yuut-I in Cundare.

PrÍmary production lr¿rs lc¡¡or¡n to be very 1olr and uas shown to be

lnsufflcient for the observed assinilatÍon (produetlon f respiration).

UsuaLLy the shrinp ate sedi-¡nent. The caloríc content of nud sanples

taken over sj"x msnths in Pink lÉs ueasured by wet oxidation gÍving an

averagc valuo of 21L"1 caL g-1 d.ry washed rnurl oT /+Í, organic matter.

ïngestion rate r¿as rneasured in--g!tu by following tho uptake of 14C Uy

shrÍmp feeding on label-led nud in the Lake. Faecal pellet production

l¡as also nneasured ålry!þg. Variation in d.ry weight appeared to be the

onJ-y factor affecting feeding or defaecatlon rates. By combining these

da-barassinjJ-atÍon effj-ciencies of 30-60/" were calculated. Conparlson

of assimilation rates wlth respiratory rates (fron regression equation)

showed that in rnost cases shrimp were not assimil"ating enough energy

a1-though they always ingested. sufficÍent; comparlson of ingestion rate

ulth respiratory rate over a range of dry welghts showed that sna1l shrinp

(-<0.2 ng) could nrìt even ingest enough sedinent. It r¿as argued that the

poor ass5.nilation rate caused. the obserr¡ed nortaJ-ity in each cohort and

the unpredictability in the tine and exbent of recrrritnent.

DECLARATTON

This thesis contains no material which has beenaccepted for the ai^¡ard. of any other degree ordiploma in any universj-ty and Ì;o the best of my

knowledge contains no materj-ai published orw¡itten by another person except r¡herereference is rnade in the text.

R. MARCHANT

ACKNOi^IIEDGIS,ENTS

The r¿ork for this thesis uas done at tr¿o uriversities:

Monash University, Victoria and. the University of Adelaide, South

Australia. I was at Monash for two years before transferring to

Adelai-d.e. I wish to thank various people at both these places for

their he1p.

At Monash the Chalrman of the Zoology Department, Professor

J.I,I. Itlarren and the Laboratory Manager, Mr. J.T. Guthrie provided

facj-lities, in particular the departrnentrs field sta'bion at Alvie,

Victoria, which they generously allowed me to continue using after

I had t:'ansferred. to Adelaide. They also lent ne various equiprnent

after I hàd. left. Mro G.D. Farrington gave me much practical help

and. took some samples for me when f was unable to. At Alvie

Messrs. Ron and Len Mather,¡s, on whose property the field station is

located, toolc the meteorological records and gave friendly

hospitaliüy al all tj-mes.

The Laboratory Manager of the Zoology Department, University

of Adel-aid,e, I4r. P.D. Kempster, was very heJpful when T first

arrived and provided. facilities at short notice. Mr. P" Leppard-

of the Statistics Department gave me advice on my calculations of

error and I4r. C.R. Jones of the Cornputing Centre ran the multiple

regression program for me.

My supervisor at both universities, Piofessor ÌJ.D. lni'i11iams,

gave me nuch ad.vice and continual encouragement; he persuaded me

that salt lakes t¡ere worth studying and. that my results were

worthwhile.

I r^ras supported at Monash by a Monash Gra.duate Scholarship

and. at Adelai-de by a Commonwealth Postgraduate Research Ar,rard.

L a

CHAPTER 1 - Introduction

Enerry flow through animal populatj-ons has been studied by those

interested in quantifying energy relations of varj-ous trophic 1eve1s.

Sonetimes energ"y flow is measured through every trophic 1evel but more often

a population of one species or a community of closely related species is

sturlied and. data collected on at least three important aspects:

1. the rate of energY intake (food);

2. Lhe rate of energy el,imination (faeces);

3. the rates at r¿hich assinilated energr is metabolised' for nlaintenance

and growth"

For a given period, usually & year, the sun of 2 and 3 'should equal 1a;,ì

represents an eilergy budget. This is one wayr no less reliable than others,

of quantifying ecosystem structure.

Unfortlnately budgets can give the impression of a static ecosystem

in r^rhich enellglr fluxes are invariable, tlius missing a significant ecological

question. 14hat controls rates of energy flow and what are theil significance

for the distribution and- abundance of animals? If some attempt is made to

discover the d¡'namics of the system by showirtg how and why the partitioning

of energy described above varies l¡ith external conditions¡ êng. temperature

or food supply, and internal conditions ¡ êc$. size of animal, or whethert

in fact, enerÐr demand is always satisfied by the ínput, then it may be

possible to ansver these questions. In my vieu the study of the energy

relations of a species must not only show hol¡ much energy f1ows, but what

physiological and ecological features control its flux once 1j-ke1y physical

and chemi-cal factors have been aecounted for.

The l.Iestern District of Victoria, an agricultural area of cl.ea.reci

volcanic plains west of ì,le1bourne, contains a number of shallow salt l.akes of

various salinitj.es and. d.epths. The shallov and more saline ones ((2 mr> 60f"")

2.

possess an invertebrate conmunity of fer¡ species in whlch the anostrs.can

crustacean @lle$g--?1g!Zigte, the brine shrimp, 1s usually prominent.

My aim has been to measure the energy flol¡ in two populations of this speeies

and deternine the major factors controlling it.

Over the last decade various aspects of the ecology of these lakes

and biology of the anirnals inhablting them have been studied. Most of this

r.¡ork has been surunarised by Bayly and t'Ii11iams (t973). The shallow lakes,

particul.arly the most highly saline (=6O%") r are desc::ibed as slmple

homogeneous ecosystems of low species diversì.ty which llilliams (f9Ze) ¡ra.s

sugq.ested. l¡ou1d be j.deal for studies of trophlc relations and ener6ç¡ flor¡.

So far a mrmber of stuoies on primary production have been completed

(Walker, I973i Hamner, l,lalker and l,Ii11iams, f973), on the less sal:ine lakes

(<lrO/"") at Red Rock, 13 km Nll of Colac, Victoria and on Lake Corangamite

(25%"), 13 km.Ït of Colac. Some of the nore highly saline lakes in the

regíon have also been stu<1i.ed. but the results have yet to be published.

The indications [Hammer, 1!70 (abstract) and l*li11iams (personal comlnunicationij

are that prinary producti-on in these is very lou because of high turbidity.

fn these lakes allochthonous inputs which are broken down by bacteria nay be

the najor source of energy (Wiltia¡ns, 1972) o ,

Much less is known about secondary prcduction in saline lakes of this

or any other regionn Paterson and lüalker (l-glA.) estimated the annual net

production of Taryþa.rus barbi!4,lq.såg, a benthic chironomid, in Lake Werowrap

(fl m north west of Colac, 3Ç56%^). In addition, l,Ialker (tgll)

investigatedthepopu1ationdynatlicsoftherotiferg@

i-ii ttre lake buù did. not estimate its production. There have been no further

quantitative studies in this region of the life cycles of zooplankton or other

aquatic invertebrates. The only seasonal stucly (one year) of the lakes

containing P. zjgtzLgtry:- uas by Geddes (tgl'). He sampled qualitatively a

serles of lakes of increasing salinity (26 km N of Colac) and r¡as able to

show that the brine slrrimp r¡ithstoocì r¡ider fluctuations in salinity than any

3 !

of the other invertebrates present and that cohorts of this animal vere

distinguishable lasting for three to nÍne nonths.

Geddes I study was part of a larger uork concerned r.lith the taxonorny

of the genus in Australia and physiological- investigations of its

osnoregulatory abilities (Geddes l)"lJ arbre). pe¡¡1¡lggie is endemic to

Australia, E_r__Ziq_t¿ig!ê being the only species in south east Australla and

Tasmanj-a. There are at least seven other species in northern and v¡estern

Australia. All have been found in astatic saline r¿aters, and P" zi.gf,4iana

in lakes ln which the salinity varies seasonally betr,reen 41.5-3OC/"". They

survive drought by laying eggs which resist both drying a.nd sal-fnities hi-gh

enough to kill the shrimp. ülhen the salinity is subsequently lor^rered or the

lalre refi11s, the eggs hatch (Geades, 1976). They also produce eggs which

hatch inside the egg sac (subitaneous), According to Geddes, as the sal.inity

rises they srvitch from producing subitaneous to resistant eggso

Parartemig is noù closely related to the bri.n.e shrimp of the northern

hemisphere Artemla sa]-l0q, another halobíont, that has been known for at l east

one hundred years (i,itttepage and McGin1ey, f965): lgþnia belongs to the

nonogeneric Arterniidae, Parqrl_emlA to the Branchipodidae. Both, however,

have the samo general form and characteristi.cally sulm on their backs r¿hi1e

filter feedÍng r.rith the setae on their legs. Food is transferred down the

legs to a ventral groove uhieh tran.sports the partieles to the nouth

(Reeve, 1963 a)o fn the r¿i1dr A. sefinê usually feeds on algae, although

Eardley (fg¡S) reports them feeding on sediments in the Great Salt Lake,

Utah. fn the laboratory they have been suecessfully cultured reaching

nâturÍty in twenty to forty aays (Gilchrist, 1960; Reeve, 1963 d; Mason, J..9Ø)

u-ith a1gae, yeast and bacteria as food. Both are strong hypo-osmotic reg-

u-l-atorsrthe mechanisms of which have been elucidated by Cr<.rghan (1958 arbrc)

for Â. sql-lna. anrL Geddes (tgl5 arb,c) for P-.--glet-z!e4a,. L major differe¡lce

between the tuo 1s that A. salina is parthenogenetic with few males occurrlng

in r,¡il-d populations (Flowers and. Evans , 1965; Carpelan, 1957); Pararte&ia

/".

is alwa¡'5 dloecious.

Surprisingly, there has been l.ittle quantitative r.¡ork on the ecologica.l

dynamics of A. salina. In general the shrSmp overwinter as resisto.nt eggs

that hatch in spring, giving rise quickly to juveniles and adul'r,s. Generatíon

ti¡ne must be close to that in culture i.e. tirlrty da.ys because they breed at

least twice in the summer pr"oducing two tlpes of egg: thin r¿a1led that

hatch imluediately and thick vallecl or resi.stant eggs tha'b overwinter after

the remaining adults die in autumn. Occasionally juvenil.es also overwj-nter.

There have been no field studies in vhich a relj-able santpl;ing scheme has been

u-sed i:o qrrantify their i-ife histo::y; mortality and natality rates have not

been measured j-n the fiel.d.. Carpetan (1957) estilnated a minimal value for

biomass production of fu._sjì.}þ.Ê in a commercial salt field in California

based upon the probable number of generations per year multiplied by the

average size of his samples. Mason (l.g6l) in a study of Mono Lake,

California, quantitatively sampled l_._Sgþ9, h,ut did not use his rj.ata to

estirûate production o¡ clarify its life historX'. There appears to have been

sporadic work on the Great Salt Lake, Utah, sum.narised by Flowers and llvans

(1966) from uhich the life history outlined above is known, but little e1se.

There is thus scant information i-n t"he literature which bears on energy flow

through natural populations of brine shrimp and no clues as to what may be the

most important factors controlling this.

Ar.--EÊLina, however, is readi-ly cultured in the laboratory (many

references in Littlepage and h{cGinIey, 1965) and here its feeding, respi-ratlcn

and growth have been quite thoroughly studiee (Citctrrist, I95/+, 7956, 1958,

1960; Kuenen, 1937¡ Eliassen t L952; Reeve, I)63 arbrcrd; Mason, t963;

von lIertig, I97L). These investigators were mainly concerned uith the

influence of salj-nity, ternperature and animal size on these processes.

Reeve and Mason particularly discussed the influence of fooC (algae) eoneen-

tration on feeding rates and grouth efficiencies. I'lo one has measured the

rates of any of these processes for r.rild populations of A. sa.lina. to estimate

5 o

their contribution to the metabolism of a salt Iake, let alone to deterrrine

whlch, if any, control survj-val of the shlirnp or horr they eompare with sue.h

influences as competitj.on or predation. Suschenya QgeZ) anil Klekowsfi (f9?0)

have combined laboratory rates into energy budge'bs but these te11 us little

about r¿hat controls energy flow in r.¡ild populations. i

To <lecide the influence of these ph;¡siological considerations on

the bloenergetics of the brine shrimp in the simple communities of salt

Iakes, field estimates of their feeding, respiration and growth rates plus

a programme of quantitative sampling are necessary and possi-ble. One

of the mo.jor eonsideraùions of this thesis is to shor¿ that field rather

than laboratory data are essential for und.erstanding the flow of energy

through natural populations of P.Jzietziana. Such si-ng1e estimates are often

dlfficult to relate to the total energ'y erçenditure of a community" fn my

case this is less true because there are no tertiary producers and energy

from primary producers r¡il1 be eonsumed nainl-y bÏ B:- 3-&j#,.There are some data on the ecology of other anostracans (Hartland-Roue,

1972) urany of whÍch live in temporary, but less saU-ne r¡aters than brine

shrimp. This mainly descrlbes various life histories and investigates

hatching stimuii. The only work in which popu-1.ation dynanics antl energetics

have been studied in the field is Dabornrs work (1975) on the l.arge predator,

B::anchinegta qig4g, in a shallow (about 1 m), turbid fresh water lake in

eastern Alberta, Canad.a.

6.

CHAPTER2-Studyarea

Phvs anil Chemical eatures

The two lakes ín which ?-M. uere st'ud'ied, Lake Cundare

(3go o9r s, l/+3o 37t E) and. PÍnk Lat<e (38o o6r s, !/úo /*or E), J.ie

approxinatrely 26lo north of Colac, Vlctoria (n:.g. 1). I¿ke Cundare is

appro:clnately 3 }rn long and 1 km r.ride, r¡ith an area of about 300 ha. and

a üean depth of 50 cn; Pj¡rk l¿ke 1s roughly squaro with a sirle of

approxinately 360 n, an area of 13 ha. and a mean depth of 1 rn. Both

lalces have flat nucl bottous conposed at least par*uly of faecal pellets

from P. zieLziana. Cu¡rdarels seclinents are fÍr"n and clayey while Pinkf s

are looser and. nore sílty.

The regional c1j¡ate (sr:nnariseil in Table f) fs cool tenperate.

Rain oecurs mainly during wl"nter and early sprlng, and was generall-y higher

than average drrring my study. Itre excess of evaporatlon over ralnfall

and the absenee of any rivers draining the region north of Colac expl.a5-n

tho preclorninance of saline lakes.

I visited the lakes approxfunately monthJ-y. Salinltyr temperature

and water 1eve1 were aluays measured. the field station of the 7'oolog

Department, Monash llnlversity at Alvle (fZ h NII of Colac) r.las used as

a base.

lvlethoäs

TotâI dissolved solids (T.D.S.) were ta.ken as the best neasure of

sallnity. Ttre;r 1¡sr. calcr¡lated fro¡n conductivity neasr:rernents using the

regression equation of HÍIIia¡us (f966) relating T.D.S. to sonduci;ivity"

Sarnples with a T.D.S. greater tl:,rrn l51%o wêrt) dilutecl because the

regression ls not accu¡ate at such high salinities (Wlfiians , L966).

l.Iater ternperature was measured with a nercury in glass thermoneter

and a rnaximu4r/rnininrm thermo¡ueter located. al¡out 30 em below the surface.

4i*"ullater level r"¡as from a datu¡o narked on a pole in each lake.

FIGURE 1

The study areao The lakes not named

are all saline. (C = Colac)

l+3o 40' E

NSWs-----a /- \

VIC

c.

I

It

3go oB's

PiNK L.

N/ \

L. CUN DARE

o 2km

0

TABLE 1

Meteorological data record.ed at Colac and at A1vie, 11 l<rn north west

Jan.

26.2

Feb.

.)8, I

May

].5.3

Ju¡e

]'3.6

July

72.O

Aug.

13.5

Sep.

15./*

Qct.

17.8

Nov.

20.I

Dec.

22.8

ïear

r8.7

I4ar. Apr.

23./+ 19.4alvlean oaLl-y

Mlax tenp Co

Mean dailyaMin temp 0o

jrfean a

Rainfall (mn)

Rainfall (o*)br973

Rainfall (u*)br974,

iainfall (r"r)br975

9.0 9.6 g.o 6.8 5.J- /r.O 3.2 3.9 /+"9 6.0 7.2 9.5 6./n

32 37 M 56 70 76 76 e6 74 68 57 L5 72L

28 136 6r I3r 106 67 3/. 73 S/,F 97 /rg

M 26 2t, to8 /+O 28 ]-53 L38 r?5 87 /+O

886

877

20

6/+@a

28 5 B/* 35 73 5r r77 130 tL6 2L2

Evaporation (rm)" 1Bo ]:69 tzo s3 /+g 33 /r3 /r9 59 gr 116 r57 rr/+g

a

b

c

Fron Ccnunon'¿ealth Bureau of Meteorology I975t Colac Station, Vlctoria

From Mcnash University fj-eld station, A1vie, Victoria

Mean values fcr 1)69 and. 1970 ai field station fron lialker (t923)

9.

Results anrl Discrrssi,on

T.D.S. (Figs. 2 and J) shows the typically uicle annua.l fluctuatlons

uhich have been recorcLecl in many of the lakes in this region (WÌ.i-U.ams ana

Buelorey, 1976), being lowest after the winter rain vhen rainfall exeeeds

evaporation. As expected, novement of the vater 1eve1 follou,s the salinity

cycle o

The chemistry of both lakes is donineted by the Na and Cl ions"

llilliams and Buckney (1.976) found their ionic proportions remaj-ned very

constant over four years. They corrcluded that, chernically, these l.akes are

very homogeneous. The average pH is B"/+ and. stabl-e in both, and the meatr

trrrbiclity (secch.i disk) ranges from 9 cn in Cr-rndare to /+9 cm in Pink

(tliltiams, personal communication) "

The water temperatu:'es are presented in l'igs. /+ and 5. The rnean

temperature at each visít is based on eÍther a singl.e reading within two hour.s

of midday or fou¡: to five reaclings spaced thrcughout tr.lenty four hours. The

readingsl¡ere somewhat erratic more so in sunmer and in Cundare, as e4pectecl

j-n shallor¡ lakes. Mean month]-y water temperatures (irnportant j-n calcula'bing

annual respiration rates) r^rere obtaj¡red ej.ther Cirectly from the mean

temperature on eaeh visj-t or by a.veraging this t¡ith the adjacent maxj-rna

and minj.ma. In this nanner the available data were ful1y u.sed attd gave

results (tables 12 anl 13, Chapter 5) which are close to the mean ntonthly

r,¡ater temperatures l,lalker (tglS) recorded in l*eke Werowrap (f; nn NW of Co.lac;

mean depth 1./+ m) vi-th a contj-nuous tenperature recor-d.er. There ís no

temperature stratification because of r.¡ind and the shallovrness of the lakes

(Hussainy, 1969).

Both lakes are surrounded by fields used for sheep and cattle or

crops. They are quite erposed to wind" Conseo-uently all-ochthonor:.s organic

material readil.y enlers the lakes and is probably their major source of ener¿¡y"

FIGUNE 2

Fluctuation in the salinity (c ) and water

1eve1 (o) ofPinkLake

EU

E=o!

=oN

_Õ

\,\,(_\J+)o>

so

o

oa,oôF

300

200

too

o

JFMAMJJASOND JFMAMJ JASOND FMAMJ JA SONDt975

bottom1973 t974

F]GURE 3

Fluctuation in the salinity ( o ) and

r^rater leve1 ( o ) of Lake Cundare.

EL)

E)

+JoE7o\,

_ô

N)

\)(_\)

at-)

o3o

(_!

o

ßU)ôt--

3 00

2 00

I oo

so

bottcmJi.-MAI'IJ JASOI'JD

I 973

FMAMJJASCNDt974

FMAMJ JASONDt97 5

FIGURN ¿.

Mean temperature ( o ) of Pink Lake on each

visit and maxima and minina between visits.

Gaps indicate no records were taken.

30

o2C^o

ro

JFMAMJJASOND JFMAMJJ,ASOND JFMAMJ J.AS.OND1973 i974 r 975

FIGURE 5

Mean ternperature ( o ) of Lake Cundare on each

visit and maxima and. mini-ma between visi+.s.

Gaps indicate no records r^rere taken.

OU

40

30

20

ro

(-!

JFMAMJ JASONDI 973

FMAMJJASOND JFMAMJ J,ASONDt97 4 t975

I/*.

Primary produetioTì is, of course, the other energy source bnt turbidity

limits j-t" The only algae so far recorded in bo'th lakes is the halobiont

dinoflagell-ate 4lna1le1la- salin.a (l{ussainy 1969) n Willians (personal

coumr:rieation) has completed a four year study of the primary product:ion

of four shallor¡ saline lal<es in this region, including Pj.nk and Cundaret

and only found very 1ow',/alu,es. Hammer (fgZO) in a brief study of Pj.nk

T,ake neasured 20-60 mg0 *-2 d.y-l, equivalent to an annual rate of ISgC n-2

- al-so a low figure.

The only informa.tion on the fauna other than P. ziel,zia,n+ comes from

Geddes t (tgl6) seasonal study. In Cundare he found three species of

ostracod: ligg1plr$. sp., Ef$cr,¡cliE sp. and AqÊ!ra1o,cvpÉE--I.9ÞU-q!e;

and two species of copepocl: Cglam-oe.cia salina and M!9,rogyqJ-gpp arnaÈdj..

In general, these only occurred during the periocL of lowest salinity ('<tOO%.),

althongh B:$y3;rp:n:þ ltas present up to I50%.; in Pinlc l¿ke he only found

the brine shrinp" My observatj-ons were simil.ar, exeept B-latfq,Ip.qlç. l¡as

also present in Pink perhaps because the average sal-inity r.tas lol¡er.

In addition, I occasionally collected larvae of the brine fly Ephvdrql-l+

and solnetirnes saw large ernerging srlarms around the edge of Pink in sumir.er.

How these other nembers of the invertebrate community interact with

¡re brine shrimp is not lcrom. They all share the sane food so possibly

competition for thi-s occurs. A feu tirnes I collected Eph-v¡Læ,]le larvae

attached to !-. z,i.@, but whether they vere eating or harming the shrir:p

was not clear.

The only laror¿n predators of Egziel,ziqa are birds. A record t.'as

kLpt of the species and nr:¡nbers seen during each vi-sit, Table 2. The

SilVer Gull (@) was the most conmon, and was the only

one that reg'u1arly attempted to catch brine shrimp. The other birds used

the lakes more as a refuge than a foocl source.

TABLE 2

Bird.s seen on Lake Cundare (C) and. Pink take (P) fro¡n Novenber 1)73 tc }lovember L975

rg73Te-keNDJFMA

r97/+MJ

200 50

+ 500 600 120

2

¿

r975.T A S O N D J ¡ }4 A M J J A S'O TSneeies

Silver Gu]-1

Lan¡s novaehollandiae

Red-Capped DotterelCharaclriu s alexandrinus

SÌrarp Tailed Sandpiper

Calidris acurninata

Red-Iiecked S',,in'r,

Cahdrís rufr-coI1isRed-Necked Avoeet

Recurviro stra novaeholLandiae

Grey TealAnas c'ibberifrcns

AusLraiian Lictle Grebe

Pocliceps novaehol-J-andiae

Musk' Du.ck

Biziura lobataBlack Sr¡an

Cygnus atralusMountain llrclc

Pad.orna radornoides

/+

/"

P

P

tr

P

P

c

P

c

P

c

P

c

P

c

P

c

P

c

20

50

? 2

L0

T2

30

I

/*

200

lr 3 100 220 30

180 100 100 15C 50 L30

22+

61

't

+

90 2OO I/+ 5 80 2

10 3/+

1

100 11 40 L5

13 lL 15 15 10 10

32 1

otr\le+)Ð It2

70

2

F\r

<D4Èo

.Fl+J16 1g¡{c)(r)poo

}4

v)

o.r{{-)sJÞHc)g>

-ooo

aal

2

T3

9

1

3o

7

200

6

a

-r species present' bu'r, tiot corutted

L6.

CHAPTER 3 - Popul-ation density of P. zie.'!z:!gq?

Reliable estimates of populatlon density are the basis of all

quantita-bi.ve fiel-<l work. In constructing an energy budget for a population

they are essential in a1l- calcul.ations and ma.ke it possible to relate enerry

u.sage to its availabil-i-ty. ft is usually easier io ,"" r,rhy we need. precise

measures of population size than it is to obtain them.

plankton populati-ons are rarely distributed rando¡n1y Ín l.akes

(George, 1¡97/+; Cassie, ]97]-). Horizontal and vertical currents or upr+e11ings

of nutrients combined r"¡ith behavioural traits such as diurnal- vertical

rn1-gration or phototaxis cause zooplankton to become aggregated or clumped.

Thj.s resul.t- j-n the variance of a series of sarnples being mueh larger than

their nean, r¿hereas they would be equal if a random distribution prevailed.

Consequently for a given effort the sarapling error increases.

Me'bhods

Samples were taken at approximately monfhl;i inter"'a1s hy prrshlng an

open galvanised iron cylinder (0.11 m2 in cross section and 60 cm high) into

the sediments, The co¡¡nn of lnter so isolated l¡as bailed out uith a bucket

through a ZOOy zooplankton net attached to the side of the cyl-i-nder in a

frarne. P" zietz,iana nauplli were > 6OOy long; their eggs uere 25fl*

in ciiameter. occasional.ly in Pink I¿ke, the loose bottom gave way when

bailing because of the surrouncling uater pressure. In such cases the shrimp

ruere collected by repeatedly dipping a smal1 zooplankton net (ZSOr') Ínto

the cyl-ind.er until no more were caught.

The cylinder could only be used in r.rater shallower than 60 cm"

Cundare was always shallover than ttris, r¡hile the shore region sanpl-eci i.n

pink uas usually so except for the ncnths October I97/+ fo March L975 and

Au,gust to Novernber 1975. I,lhen the water r,¡as too cleep a standarcl zooplankton

net (25Oru) *ut towed vertically. The area of ttre rncuth of thís net vas

O.o7 m2. Therefore the catches vere multiplied by 1.56 (o.II/o"O?). These

17.

vertical haul-s were calibrated by taking four series of paired samples with

the net and the eylinder, one i¡ Cundare and three in Pinlc (taUte 3) '

Significant statistical differences could only be shor.rn tr¡ice using t'he

h,ilcoxon signed-ranks test for paired samples (Sotal and Rohlf, L969) t

although the corrected net catches were alïrays smaller than those of the

cylincler. If all the data are combined then the net eaught significantl¡'

fewer (p =0,005, one tailed test; n = 31) shrimp than the cylinde::t the

average efficiency being 65%. This faetor was used'bo correct all sanples

taken with the net.

prelirninary samples taken before November 1973 indicated a con'i'agious

distributionofP.z,ietzianainbothlakesrbutmoresoinPink'and'thusa'

high sanpling error. Precision was improvecl in two ways. First, the

number of samples taken on each visit was increased to sixteen in Pink and

twelve in Cundare. This occupied' a vhole day in each caseo To reduce the

error to Io% r¡ith the degree of contagion encountered would have requlred

approximatelyonehirndred.andfiftysamplesfrombothlakes.

Second,variancewasdecreased.bystratifyingthesamples.To

aceompllsh this the habitat is split into sub-areas or strata r"¡here it appears

- numbers per sample will be similar. I had observed that wj-nd generaterl

currents caused the shrimp to accumul-ate against one or two shores of tire

lake., Therefore the four shores of each lake were considered as st::ata.

The benefit of this rnethocl is that when caleulatlng the total standa:'d erl"or

a weighted mean of ';he variances from each stralurn j-s obtained thus ignoring

heterogeneity between them due to the vi.nd. sampling effort v¡as

jroportional to the relative a'ea of a stratum" In Pink Lake four

sanples were taken on each shore because the lake ís roughly square. 0n

the other hancl cunoare is rectangular vi.th the long sicle (four samples) Ueing

about tr¡ice the short ('bwo samples). In both lakes samples were spaced

along the shoz'es not clumPedn

The samples lrere preserved on the ctay of c'I1ection in IAl" fonnalin'

l_8.

TABLE 3

Calibratj.on of the zooplankton net (ZSO¡) againstthe QLLrn¿ cylÍnder. Catches r¡ith the net havebeen multiplied by I.56 before expressing thern aspercentage efficiency.

L¿ke Net efficlency (/") signed ranlcs test for n pairs (one talled)

notsignificantrn=L2Cu¡rd.are

L6 Qct'. 74.

Pink

1 June 75

Pink22 Jwrc 75

PinkL9 JuL. 75

Mean

79

83

65

/+9

l+7

p<.0.05ril= I

notsignificantrn= I

p<0.05 r D= I

p<0.005r n=31

19.

Each sample was eounted r^¡ithin three rnonths, the varÍous cohorts presenb

being treated- separately. Occasionally sutrsampling of indj.vidual saml:les

vas necessary. Animals r,¡ere selected from a randomised mixbure of the

sample with a uide mouthed 50 ml bulb pipette until at leas'b four hundred

hacl been counted. The distribution of these snbs¿mples Lras found to be

::andom just borderi-ng on an even distri-bution; no size appeared to be

favoured.

Before calculating the 951" conf::Ldenee limj.ts of the stratifieci

sanples the data lrere converted to J-ogarithns as sr:ggesterL by }llliott (19-11)

for contagiously distributed, populations. The resulting logarithrnic

confidence limi-ts were converted to the arithmetic scale and combined t'¡ith

the arithmetic mean to give the actual confidence l-imits. This is a hybrid

rnethod beeause strictly speaking the 1og method provides confidenee limits

for the geometric mean. However, aceording to Elliott (personal

communication) the arithmetic mean j-s the best unbiassed estimate of the

mean density of a finite populatÍon even if contagion prevails.

Results

Population lensities in both lakes ?re showr in Figs. 6 and 7.

There are at least two distinct generations per year and in Pink usually

threen These u¡i]I be deseribed in detail in the next chapter with the

clata on life history.

The densities are given per 0.1 n2 insteacl of o.l1 m2. The

figures r¡ere not decreased to allol¡ for this because no significant ovcr-

esti¡ratíon would result. Preliminary analysis harl shown at nost 5/" of a

sample could be lost in the debris and mud that u'as inevj-tably collected

along l¡ith the shrimp. Another 5% or less could be Lost in the actu.al

sampling procedure. The 10% increa*se to 0.11 m2 cou-l-d thus reasonably

be balanced by these losses; the confidence limits of the nean vlere always

greater Lhan IO%. Saupling per uni-t area $¡as chcsen instead of per unit

volume for ease of calculating production (see nerb chapter), which is

FTGURN 6

Fluctuations in population density of P-. zietziana in

Pink Lake; bars indj-cate 95% confidence lilui-ts.

. - samples taken Lrith 0.11 m2 cylinder

A - only 12 samples taken

o - sanples taken with zooplankton nef (25o¡ )

X - samples taken during calibration of net agailstcylinder

Numbers refer to the variouõ generations d.iscussed. in the

nexb Chapter

I ooo

roo

ro

4

3

2

ó5

7

Nl7tr-o(-C\)oE=C

r973 T12 ¡1 n- t,ll g74Jí t J Ð t\J ò ft iu TgzSJ t 3o

FIGURX 7

Eluctuations in population density of þþ@!ry, in Lake

Cnndare; bars indicate 95% confj-dence limlts

. - sanples taken r"¡ith 0.11 n2 cylinder

A - sanples taken on only three shores

- samples taken during calibration of netagainst cylinder

Nr:mbers refer to the various generati-ons discussed in the

next Chapter.

X

4

rooo

roo

ro

ôT5

EöL-\,,

_oE=C

¿

3

c_!

t975t9741973

22.

ah¡ays based on area. Preliminary sanpl-ing had shoi^m that both unÍts

produced just as variable data.

The r^¡idgr of confidence limÍts (LO-50% of mean) implies that the

3571 wñ.erestimatj-o¡ by the vertica] hauls (ta¡te 3) was usually not

sign-lficant. I{owever, the paired samples, which.largely ignore horizontal

¡eterogenejf.Xr shcwed that thj.s underestimation was significant. îhereforet

the correction should still hold even if it j-s relatj.vely unimportant in

the final es'bimate of the lrêâno

To separate the individ.uals in a sample into cohorts I used analyses

of size frequencl," The daba for this r,¡j"Il be given in the nexb chapter.

In most cases it vas easy to decide to which cohort an indivichral bel-onged.

Inevi.tabl¡,, the size class at which the üivision occurred was mo::e or less

arbitr.ary, but the proportion of the populatiorl this representerf l¡as

insignificant.

Disoussion

, rn general, I believe, the sanrpling was adequate because stab1e

trends energed and. the varjability vas not so great that signifj.cant

dÍfferences could not be cletected even l,'etueen rnonths' Tn other vords the

salnples r¡ere at l-east representative.

No signi.fi,rant bias r¡as introduced by taking samples near the shore

ín both lakes. Pirk I¿ke was al.most twice as deep in the midclle (1 m

approxinatei-],) as it waí; ne{ìr'the sides. Ho}reyer, there WaS no correl'ation

between volume or depth of water in one sarnple ancl the size of the catch.

Nor r,ras theqe -any i.rregular variabilii)' j'n mean shrimp density as would be

expecteil fron such a correlation in a lake fairly constantly stirred by wincl.

R:rthermore, P¿-lj$¡M often appeared to congregate near the botton"

Thus the shrirrp r¡o':lcl r,end to be distribu'bed by area rather than volume

making any influenge of the uater eolrunn on population density even less

líkely; later work chows they are largely bottom feeders. I'inally, i.f

23"

they had been evenly spaced through the water column (fO-10 cm) then no

signifi.cant dÍfferences r¡ould have been eryected' vhen calibrating the net

agai-nst the cyli¡der; the net uould have filtered completely a colunrt this

length.

l,later depth cor.ùd not influenee sanpJ-Íng ip Cundare because depth

was the same (-<50 cm) virtually to the eclges of the lake. However, there

was once a significant increase in shrimp density (October to Deceinbet 1974)

that could not be explained by recruitment. This largely resulted from a

numbe:'of blank samples in October and Nover¿ber, possibly due to Írregular

currents a

llind is the other i:nportant factor in the distribution of P. zi7-tTlqna

in these lakes. The circulation pattern of wÍnd ind.uced crtrrents in shallow

lakes has not been well studied. However according to SuLith (].gZS) tn a

shallor¿ cj-rcuLar lake longshore cunents would. result from water blom tot¡¿rds

the Iee shore rather than the vertical circu-La't,ion typical of deeper lakes '

This vouJ-d account for large mrmbers of shrimp often founcl clumped' along only

one or two shores of Pink. In Cu¡dare this also occurred, bu'b not to the

same exbent j¡rdicating perhaps that longshore currents are less well

cleveloped. Iil fact, the only random distribution oecurring was recorded

fromthislakenThed.etectionofclrrnpsdepencsatleastpartlyontheir

persistence. Behavioural responses of the shrimp to the strength and'

d.irection of currents wculd und.oubtedly ÍIfluence thi.s.

To some exbent the probability of longshore currents justifies

using the shore as a stratr:m. However, the variances within each stratum

wLre often large, sometimes of the same order of nagnitud'e as the total

varia¡rce without stratificationn This lms e>çected because it r¡as intpossj'ble

to redefine the strata on each occasion to suit the rsind direction. It

seems urat in these shallow lakes the main advanta.ge of stratified' sarnplingt

conpared r"¡ith rand.om, is its greater efficiency. By chance a series of

random sampleS coul-d. well have missed large clunps of shrirp blor'nn onto one

4.

shore. In contrast stratiflcation ensured that a nore complete range of

shrimp d.ensities was represented.

Samples in each strata r,¡ere not picked at random but spaced. apart

along the shoreline, more or less evenly. Provided they do not coincid.e

r.ri.bh any repeated pattern 1n the popr:lation then according to Tid¡narsh

anil Havun ga (wSS) the samples can be treated as an equivalent number of

randon points to which the usual techniques for measuring di-spersion can be

applied. I{owever, there is no simple nethocl of calculating the confidence

limits (trIliott, personal conmunication) for the arithmetj.c mean of smalI

samples fron clumped distributions. The nethod of converting the data to

logarithns before calculating the dispersion and combining the reconverted

results with the arithmetic nean provid.es confidence limits t¿hich are

probably too wide.

25"

cHAPTER/+-Lifehistory,grovthand'p::oductionofW

The da.ta on population d.ensity can be used to esti¡rate mortality.

I'rom additional data on life history and. growth producti.on can be deternúnecl.

This is conveniently calcuJ-ated., for an aninal such as P" zíet'ziana with

distinguishable cohorts, by integrating Al1en curves - graphs of mean number

versus nean indivi.dual weight.

Biomass produceC during reproduction is not i-ncluded in the above

estimation, but must also be considered. By measuring f'emale clutch size

this contrlbutj-on can be assesseC, if the survival of ovigerous females,

the number of clutches produced and the weight of their reproducti-ve products

is lcror,m. Finally, for crustaceans, the weight of noulted exoskeletc¡n

should be added. because this represents biomass gainedr but subsequently

Iost. In practice it r,ras lnrpossible to collect the fragile exuviae.

However, their corrtribution j-s likely to be negligible conpared Ìr:ith

sampling erl'orso

llinberg (fgZf) and Edmondson and l.Jinberg (fgZf) reviet¡ed the various

numerical method.s used to calculate production of aquatic invertebrates

fron the precedj-ng type of data. Sone of bhese assume fixed. patterns

of growbh and mortality" Al1en curves, r.¡hich are plotted from ernpirical

data, do not.

Methods

trbom each series of monthly samples at least one, unpreserved,

uas e:<amined on the day of collection under a dissectj-ng microscope. The

shrj-np r¡ere sorted into arbitrary length classes, r.¡ashed wi-th freshwater

and placed. ir, vi-als in a desiccator" l,Jithin at most one week they we1.e

properly dried in a vac'¿um desiccator at 6OoC and. then stored over silica

ge1 until wei-ghed. Rarely was there any bacte:ial contanination before

this was d.one. A]-l lengths were measured in arbitrary units l¡ith a

micrometer eyepiece at a magnifi.catlon of 6.3, tlne length oeing the distance

from the join of the second antennae r¡ith the head to the tip of the 1;elsont

26.

between the two cercopods. The remaining samples fron each vi-sit,

preserved ín IO/" fornalin, r¡ere arnalgamated after counting and at least

one hund.red shrirnp subsampled to determine the length frequency of the

popr:lation; when the catch was snall all were neasured. Any shrilkage

from preservation in forrnalin had a negligible effect because the mean

length of preserved individuals Lras never significantly different from

that of unpreserved. The number of ovigerous females j-n each length

class r^¡as always noted. They were considered a separate class when sorting

the sample used for d.ry weights'

All dry lreights were measured to a precisi-on of t O.O5 *g. A

li¡rear regression between the logarithms of mid-class length anrl dry lreight

of the arbitrary sj-ze classes (f:.g. e) enabled the mean ind.ividual weight

to be calculated at eaeh visit fron the length-frequency data. Ï'Ieight

due to the egg sacs of pregnant females was not included in these

calculations.

The clutch sÍze of the ovigerous females was deternined by dissectfug

the egg sacs of preserved animals. The frequency of clutches r,es noted by

raising p. zie'vziana in aquaria at 18oC to 2OoC, the temperature range over

r+hich ovi-gerous fe¡nales were usually found. j¡r the lakes. Shrinp for this

were collected at the ICI salt works, Dry Creek, Adelaide and brought to the

3-aboratory within an hour. The dry weight of the reproductive products

was calculated by subtractj-ng the dry r,rei.ght of a non-ovigerous female of a

particular length ciass (fron the regression equation) froro its dry weight

r¡hen carrying a f\rI1 egg sac.

Resu].ts

(") Life storv

This is best understood fron the length-frequency hi-stograms (Figs.

9 and 10) together r¿j-th the population tì.ensity cu-rves (figs. 6 and ?) fron the

last chapter. tr'Í-gs. l-L and 12 summarise the groirth of individuals in the

FIGURE B

Mid.-class length of PÆzfana versus mean dry

weight" Nrmbers refer to the size classes in

arbitrary units. Th-e regression eciuation leJating

length (run) to dry weight (mg) j.s:

rr - r"/+Àp x 1o-3 12'63 (n = t-1!, 12 = o.99)

ol5l2

a

ll¡

ro

9

It.oo

o.to

o.ol

7

ctìE+J_c..9\)3

(-e

4

5

ó

3

o2

a

2

løngth mm

to 20

FTGUR^E O

T,ength-frequency of P@ in samples fron

Pink lake based on sixteen samples per v5-sit. Open

histograns represent ovigerous females; a vertical

d.ash indicates the separation between tr,ro cohorts.

I ovigerous females present, but at a frequency2/"

* histograms based on onJ-y one or tr¡o of thesixbeen samples

histograms based on on1y one sanple takenqualitatively

nr¡mber of shrinP measured

t

n

11 Oct. 73(n = I0!)

ll Dec. 73(n = 98)

l3 Feb.74

lO Mar. 74n=16)

I

-h

?9

9ç9

9 Nov. 74(n = 174)

9 Dec. 74(n = 167)

14 Jan. 75(n = I30)

ll Feb. 75(n = 2I2)

16 I'lar. 75(n = 275)

I Jun. 75(n = 24rl

22 Jun. 75(n = 125)

16 Àug. 75(n = 263)

9E

*-J 9

H

t ,n = le5*)

-.. Æ.---

E20 Apt. 74(n = 57)

22 l4ay 'l 4(n = 4)i*l

16 Jun. 74(n = 359)

20 .tuI- 74(n = l7B)

3 Sept. 74(n = l-77'i)

3 Oct.. 74(n = 132'i')

I

-¡19 Jul. 75(¡r = ll4)

t

i3 Se¡>t. 75(n = 165)

o

roo

_o 50 ? 9ç I

ll Oct. 75i¡r - 194)

¡J l.Jov.75(n = 115)

14 Oct. 74(n = I44)

ç

t23 4567ggloilt2t3t4t5 I 23456I I9tOilt2r3r4rsrnid-clcss løngilr in clrbitrcry units

F]GURE 10

Length-frequency of Pn ziet,ziana in samples

from Lake Cundare based. on tr^¡elve samples

per visi-t. Open histograms represent ovigerous

fenales; a vertical dash indicates the

separa-bion betr¿een ti¿o cohortso (Symbols as

in Figure P).

I

12 Nov. 73(n = l4l*)

12 Dec.73n = l2'lt)

17 Jan. 74(n = 173)

20 llay 74(n = I29)

3 Oct, 74( n = 76'i')

15 oct. 74(n = 203)

l-O llov.74(n = 159)

ro D;;. 74(n = I37)

15 Jan- 75(n = ll2)

l2 I'cl¡. 75(n = 120)

.\1.1r. 75

9

II

Y?

?

roo

ro 50o-

17 Jun. 74(n = 294*l

t-t-r E

2l JuI. 74(n = 96)

3 Scpt. 74(n = 150'l')

23456789tOilt2t3t4ts

? T7(n

T

I234567b9tOilt2t3t4t5

mid-class lungth in crbitrary units

FIGURN 11

Growbh of P. zietziaria in Pink Lake. T]ne 95% confidence

lilrÉts are shor^rn by the bars except where they are too

nAffO'l¡Io

Ovenrintering generation, 1-973

Early srrrrmer generation, .1973

Autu¡n generation t I97 /+

Overwintering genera'cion, I)7 /.,

Mid-srruner generation, ].97 5

I4id-winter generation r,I9T 5

Spring generation, 1975

1

2

3

4

5

6

7

Crr

E

U=.C)

:>-o.CCoo

4J_C.9Ò)3i._'oCoNE

2.O

t.o 3

5

2

ó4

r973 1974 r975

FÏGURE 12

Growbh of P. zi eLziana in Lake Cundare. The g5/"

confidence linits are shor,¡n by the bars except where

they are too narro'hr.

Mid-r¿inter generation, 1973

Overr"¡intering generat ion, 1973

Autunn ger¡eration, 1-97 l+

Overwj-ntering generalion, I97 /¡

Late Sunner generat'ion, 1975

1

2

3

4

5

3

c¡-

U=p.

!.çCoo-P_c..9\,,3L-¡oCo\)E

2.o

42

r.o

5

t975t974t973

32.

tr¡o lakes.

Shrimp frora the overwinterÍ-ng generation, the only one present in

pink lake in late l9"l3t grew steadily reaching maximm size in autumn I97/+,

l¡ut at the same time most died. because of salinity increasing over sunmer

(pig. Z) to Ieve1s at wh-i-ch significant mortality occurs (Geddes , I)75 a) -

A smal1 early sultÌmer generation hatched as females becane ovigerous but this

died ou.t quickly, also frotn increasj¡g salinity" The size frequency

distribnticns of the ovezwlntering generation from January Lo Itpri.1- 7-97/+

are unsteady ancl this is reflected, j.n the growth culveo In fact, it seems

at one stage (February) tnat recruitnent occurred to the l-arger sized

cohort. Ìlowever, the January and February histograms uere based. on only

one or two samples rather than on the sirbeen usually taken vhil-e the

Idarch and Ap::il sanples Lrere very smal]. Thus sampling error is the

probable e4planation for this erratic gror'rbh'

In lø.ke Cunclare during thÍs period the rnid-vinter genera-ti-on

present also died out, but sooner and. vithout any females becorling ovi.gercus

to prod.uce a su¡nmer generation. fbom prelinrinar"y sarnpling I think the

1-arger size cohort r.¡hich disappeared after the fírst samp]e was an

overwinterSng generation from l¡hich the smaller sized one hatchecl in

rnid-t¡i¡rte::.

After the above average rain in Apr1l and the consequent rapid' drop

in salinity eggs hatched in both lakes and. grew quickly, some to becone

ovigerous wj-thin three weeks. These eggs mrst llave been resistant or

resti:rg becau5e Cundare was dry in March and the::e uere very fet't ovigerous

i'emales in Pink during April. In May there uere two weLL defined cohorts

Í¡ Pink, hut by June these had arnalganated" The population density of the

Ia:,ger sized cohort in ì.fay was signi-ficantly less than that in June

(0.05>p= O.O2; í = 2.27t ð,f = ?J+), indicating that .bhere must have been

recruitnent bett¡een visits, most like1-y fron tlie smaller sized cohort

present i-n l/tay. Therefore considering the two cohorts in May as one

33.

generation, its numbers remai-ned constant at first and then declined as

the ovigerous females died leaving only imnatures and" some large males.

These disappeared by September'. The grolrth of an individual in this

generation llas rapid reachJ-irg a fair'ly constant maximum sj-ze. Because of

good survival of fe¡nales to naturity the oven"¡intering generation produoed-

was large. Starting at about dOOO m-2, the shrimp d.ied at a more or less

constant relative rate throughout the duration of thÍs generation (one year).

Individual growLh was rapid to start, but stoppeC for about four nonths

until Decernber. Then the weight significantly lncreased and kept on

doing so until all had died by June 19'15,

In Cundare the autumn generation grew even more quÍ.ckly than irr Pink"

The or,,erwi:rtering generation which it produced. lasted. ten rnonths. The

growth of individuals was steady during this period but their rnortali-ty

rate varied. After initial rapid death numbers stabilised through spring

into summer r¡hen increasing salinitÍes again caused some mortality. By

the tine sampling stopped in this lake in March 1975 a late sul¡oer

generatÍon of stable density, but high growbh rate, had arisen.

Salinity did not reach high enough 1eve1s over summer in I'ink to

cause any death and the overwj-ntering generation produced eggs at first

slouly and. then more rapidly fron october to Feb¡uary 1975. These formed

a nid-sunner generation that lasted the autr:¡nn apparently l¡ithout losst

but diecL rapidly rluring l¡inter. However, i¡dividuals had' natured by early

r¡inter and producecl a mid-winter cohort. These in turn natured quickly

and despite high mortali-ty produced a spring cohort before the generation

ènded. in November.

In a1I generations in both lakes males aluays reachecl a larger

naxinrum size than females. Such dinaorphisn ex-nlains the increasing

confidence l-imits around the mean weight d.r:ring g::orrbh. It i¿as diffic''¡l-t

to tell precisely when both sexes reached rnaturity, but they'were

d.isti¡guishable by the fifth size class (B.O run). Geddes (lgn) determi¡ed'

3/r.

fifteeninstarsinWianabeforehecon9idered.itadu1tat8.10tiuland three to four instars af-ber this maín1y representing gror,rth of tlie

nales.Manyofthesrnallerinstarshavebeenamalgamated'bymycjroice

of length cl-asses. 0n1y fenales larger than or equal to the six'uh size

class (=-g.5 ¡rur) became ovigerous. fn fact females rarely greu larger

gran the eighth size class (12.? uun) as Geddes (lgll) also fou¡d arrd

females were only seen copulating with larger males" How much larger a

rnale had. to be was not icrol,rn and so a nale the salne size as an ovigerous

fenale nay not have been ntature. Thus a meani-rrgful Sex raticì i's inpossÍbIe

to calculaten Houever, males were not rare ancl P " -zi9t'ziat"a' i's certainly

dioecious not Parthenogenetic.

Except after the suuner drought in early 19?lr. wlrerr the auùunrn. coil'or.t,s

in both lakes rnust have hatched from resting eggs (probably stimulatecl by

falling salinity), ovigerous fe¡nal-esi wele always presena; r'rhett nauplil tre'e

caught. Evidently, these cohorts emerged f:'om rece¡tly produced (su'bitsr'reous)

eggs.Si.grrificantrainfallsor,reLime$precederlsuc}roccasiong.

Geddes (tgZl, 19'/6) recolded this quj.te often a'nd suggested the sut'secìuent'

salinity drop triggerecl. the process. Houeve::, it may not be the only

factor. I fou¡d a period of heavy rain arrd falling salini"tyt

July-Septe¡nber ]:97/+, during l¡hich there was no recruitment; Gedd'es

noticed several. Recruitnent from subitaneous eggs a]'so occurred vhen

salinity l¡as increasing, although Geddes clailns l. gielzia¡"e. switches t'o

the production of resting eggs at such tiroes. Thus hatchírig stí-:nuli

arenotvellcharacterisedforthewet.berpartsoftheyeaT@

(b) Breedine þrBlogY

calculation of the absolute ntunber of females, e'l'asse'l as oviget'ou'*st

reveals that they rarely surr'1ved much more than one rnonth' I'{ost thab

!¡er:e caught had either empty egg sacs or only ôerreloping eggsi very

rarely clid. fema.les gÌow larger than the maxinun s;ize aL r¡hich i;hey r'rere

35,

observed. ovigerous (length class !). Mry' interpretation of this is that

females only procìuce one clutch and that they die soon after releasing it'

If ürey have raore than one clutch, by producing eggs continuously, then

fennles with ful1 egg sacs r+ould. have been conlmon in my samples. Attempts

to culture P. z:j_ eLziana support this conclusion. Those that laid eggs

toc¡k between eleven and twenty one days to nattre at about 2OoC before

copulating. The fe¡nales produced one clutch which they bore for a l¡eek

and then invariabl)' d-ied either before or r'rithin one or tr'ro days cf

shedding their eggs.

The clutch size of atl groups of ovige::ous females that developed

rrag neasured except those in Pinlc during tne L973 t'o L974 sunmer (ta¡1e 4) '

They are within the range GedCes (lglO) recordecl during his sturly

(fgZO-Zf) of these 1akes. There uas never a significant regression, i'eo

slope d.ifferent from zoro, betveen clutch size and length of shrimp except

perhaps in the october 19?õ sanple from Pink. In th-is case the amount of

varj_ation in clutch size explai-ned by length of shrinp u¡as approxirnately orie

third ("2 = 0..i.36). In subsequent calculat-i-ons of egg production Ï have

considered that fenales at one period of recruitrnent had the same clutch

regardless of length; they mostly occupied only one or two length classes

at these t1nes.

The dry weight of the reproductive products is shor'rn j-n Tabl'e 5'

Not orrly do the eggs accorrnt for this bionass, but so does the lreight of

the accompanying 3gg sac. Thus the values given are weight of an egg plus

unit of egg saco The increase in weigh'b of lnales due to speTm prodüction

vas consi-dered. negligible. hrith the value for mean weight per egg it is

possi-ble to calculate the clu'r,ch size of females during t]no 1973 to I97/+

sunmer recruitnent using the mean dry lreight of ovigerous fenal'es collecteC

in this period (1.18 rng; only leng'ch class ? ovi..gerous). The ciutch

size uas 2I./r (! 2.5).

TABTE 4

Clutch size of ovigerous fe¡nales for nonths r,rhen present and the average e1u'vch si.ze for theperiods of recruitment. 0n-1y feraales r¡ith fuj.l egg sacs uere d.issected.. The bracketedvalues are not significantly different. For Cr:nd.are '',he grand average i-s the best estinate ofclutch size because of the sna1l m.rmber of fe¡rales dissected

-L

clutclr size (!95%-confidenceIt-nl_ts /Month

April 1Ç7laMay 1974.

Ðecembe¡ 197/+Febn:.ary 1975March l-.975

Jt¡ay ].975August, 1975

October 1975

tflay I97LJwte 197/+

January 1975February 3.!75

nr:mber of ovigerous fenalesdissected

lo/r

935

lr1181

4/+

75

41,.L2.)ó.

ÓU

ôto)

B5

PINK@.(t 8"

a

)32

10

6-e¡ (irs"e)6 (t l"z)t (i 3.t)

))I

l]

))

average clutch size(I

"oñriaence lini'bs) for

period of recr.ritment

29.6 (! t.5)

39.3 (t z.e)

85.t (,! 9.6)

105.0 (irO.5)

-Lit23.9 (:L7./r)

trg.5(!r4.5)108.0 (!zS.e)

length classes(arbitrary) withcvi-gerous females

o-t

7-8

7-9

7

.9 (jtc.6)

.o (!lg.z)

105.0 1trC"5)

))

ì

\¡)O.a7

I/+T2BI2T

6-8J5

to2.o llal.l)l-11.6 (=5lu.Z)

TAB],8 5

Dry weight of an egg plus associated egg sac. Ïlhen length classeswere lumped a weighted mea¡r was iaken to calcu.J-a'ue the weight of thenon-ovi-gerous female

-2dry weight (me) of ovigerousfemale vith ful1 sacs

2.70

2.2/',

2.59

2.30

3.38

5./*5

1.E6

2.'-l2

month

April 1974

Ma¡' A974

Ifay L97L

Ju:re I97/l

June !97/+

Jarvary 1975

January 1975

July 1975

numberr^reighed.

lengihclass

clutchsize

dry weight (mg x 10per egg

) r,ate

/.

1B

18

7

7

ö

7

6c)

10

ryó

l-Õ

79.6t

95.r*

o< rê

TI9.5

TT9.5

ILg "5

r79 "5

85.g

1_"59

7-./r8

I./+7

I.23

r.83

anõLtll

0.7i

!.83

Pink

Pink and. Cundare

Pink and. Cunoare

Cundare

Cundare

Cundare

Cundai'e

Pink

2

7

1

/,\¡)-la29

r"b]-

! a.ú (95f. contideace limits)

a = r,'eighted nean of clutch síze in Pink and Or:¡dare

38.

Dlscussion and Production estimates

The data on life history and. popul-ation density show that there is

no regular period of recmitment to the P, zi-qØ'i.a:\a populations in either

lake. In general there was a population i¡crease after a drought tlrrough

hatching of restÍng eggs. Dr¡¡ing wetter parts of a year the sti-muli

causing hatch-ing of subitaneous eggs are unclear, and. the number of

gcner.ations 1ike1y to arise are not predictable. Recruútment r¿as usua]'lJ¡

suj-ft except over s¡¡ilner' in Pink r¡hen it cou-l-d be slol¡ at first as ouly snal1

numbers of fenales were maturing.

The life span of the cohorts varied from three months to a year

depending partly on whether they survived periods of rising salinit'y'

Geddes (1g16) found the sarne variation during his survey. As already

noted. there is continuous though variable nortalj-ty of these cohorts even

though the salinity is r¡eIl rvithin the tolerance linits of P@M,

(6.2 and 267/"" at 18oC, Geddes, ig75). fn fact mortality of the shrimp

can only be ascribed. to salinity during sunmer d.rought. In Janua::y and

February I97/+ Iake temperatures reacheð, 25oC zurd. saljnity was abòve zCO"/o".

Geddes (tglS) experimentally found a 60/" nortality rate in seventy tt¡o hours

r'ith this conbination. The nexb sr:rnmer temperatures were lor¿er (about 20oC)

and salinity in Pink did not rise to levels at r,¡hich he found significant

mortality although it did i¡r Cundare. For the rest of the study salinities

l¡ere betr,¡een 50 anð, I5O%, and teinperatures between -l-O and 2OoC, conditions

in which Gedd.es foirnd less than IO/' nort'ality after seventy two hours.

The probletn nour is to explain shrimp mortality dr:ring times of

iavograble salini-ty and. temperature" There Lrere no predators of any

significance, Observations on seagulls indicated that they peclced at the

water surface, presumably at shrimp, between '"hirty antl sixby time'c a ¡nj-nute"

Tt was impossible to deterrnine hov guccessful this was, but assurning

(generously, I think) that a gu1} could capture cne shrimp a' ninute and that'

there vas an average of fifty gulIs present each tLay on Pink from June 197l+

39.

to June 19?5 (Tab1e 2), feeding continuously, then they would have only eatet:

0.5/" of the overwintering generation. This is insignifican'b and probably

an overestinate.

The obvious renaining cause of rnortality is food. or energ'y shortage

either through an inabi-lity to assinilate sufficient because of the nature

of the food or through cornpeti'bion for a scarce resource. so far there is

rro dilect evidence for either and solution of this problem ui11 require

data on the nutritional balance of fuieLziatta" Gror,rLh of the shrimp will

obviously be affected by food shortage and also perhaps by temperature and'

salinity.

Growth was not sigmoidal (nigs. 11 and 12). Semilogarithmic p1.ots

gave straight 1ines, indica.ting e>çonenti-a1 gror^rLh with the animals reachì-ng

a more or less stable maximun lreight. In other words, there vas no inflexion

in the growth curve and consequent decrease in the growbh rate as maxj-mum

size r¡as approached. This is contrary to the sigmoidal gror'rth pattern

Reeve (tg6Z d) and }[ason (rgæ) found for A. saU-na in culture and Daborn

(Ig75) for the giant fairy shrlmp B" piqas in the l¡ild. Further comnent

cannot be made until the influence of the nutritlonal status of P.- zi-9-lzigllg

has been assessed.

The only exception to the ex¡ronential pattern (ttre lack of growüh

in wj-nter and spring 397/+t Pink) largely results from the frequency

distribution for July being too skewed towards the larger lengths probably

through sarnpling err.or. trow temperature had iittle influence because there

was rapid growbh during the following winter and spring. rn cundare over

the same wj¡'ber there was significant growth. In fact, the shrirnp appeared

to be able to d.eve1.op and grow quickly in any season no matter r'rhat the

temperature or salinity. In contrast Geddes (tgl|) fron his seasonal- study

suggested that salinity controlled final development to maturity. He found

that while salinity r,¡as stable during winter and springP' zj-e1ugilng

remained largely in im¡oature stages. It was only wlien salinity ine:'eased

lrO "

dur5-rrg Sunmer that most became mature, laying I'esistant eggs to ensure

survj-val over the drought. This uay have been an ad.aptation to the

higher average salinity dur5-ng his study; such an effect was not a

strong influence during mirreo For i-nstance, shrimp in Cundare d.ied. before

the drought at the begiruring of 1974, without beconing rnature.

The evident progression of shrinp through the size classes

(figs. p and 10) especially durÍng periods of little or no mortality e.g.

"u\1cohort 5 in Pink from l"larch to June [!llS,

indicates gz'owbh was gener:ally

not affected by size-selective death" l"lean maxinum weight is probably

lol¡er than shor,rn, as death of ovigerous fenales rnay artifici.ally cause

an increase. This r,¡i11 not sígnificantly alter estimates of production.

Occasional-ly amongst matu-re individuals, mean weight decreases by the nexb

visit.Significant decreases eog. July-August' L975 (fig. 11) have been

allol¡ed for in the Al-len curves (I'igs. 13 and 1/+) as they provide the best

estirnate of the weight of those dying. Otherl¡ise the curves Llere drar,rn

averaging insignificant anornalies Ín growbh or densi-ty. Production llas

calculated by measuri.ng the area under each curve with a planimeter.

The death of irnnratur.e shrirnp i-.e. i.ndivi-dual weight less than 0.6 mg or

length less than 9.5nm (sixbh length class), accounted for the najolity of

this in most cases. There were two cohorts (those hatched after the

drought in autunn f97/+) in which thj.s did not occur. In both there nay

have been significant mortality before the first sainples uere takent

irnplying prod.uction has been under-estimated" Because the d.ry t"eight

Of an egg is about three tirnes that of an individ.ual in the first síze

class, procì,uction equal to Ínitial cohort densi.ty nultiplied by dry weight

of an egg was subtracted from the estimates for each cohort.

Ìrteight of eggs produced r,¡as calculated separately" The density

of ovigerous fernales per visit during a recruitment peri-od i¡as ia:om from

the size-frequency histograns. From this the number of f'enales per 0.1 m2

FIGURE ]-3

A11en curves for the cohorts of P. zieLziana in

Pink Lake" Numbers shot^¡ the order in r^¡hich the

samples r¡ere takeno

500

500

4000

4

2

LO

11 Nov. 73

- 20 Àpr. 74

2O Àpr. 74- 3 Sept. 74

16 Jun. 74- L Jun. 75

9

3a

500

soo

roo

14 oct. ?4- 13 Sept. 75

19 ilul. 75- 8 Nov. 75

4

13 Sept. 75- 8 Nov. 75

e 4

2

(t,E-oC-\¡oE=C,

Co\)E

3

2

7

2.o r.o

3.

3

møon dry v'rcight of on individuol mg

2.O

FÏGURE 1/+

A11en curves for the cohorts of P. zieíziana in

lake Cr:ndare. Numbers show the order in r,¡hich

the samples were taken.

.2 12 Nov. 73- 14 Feb. 7¡l

too lo

5

3

ô¡

'Eöf-\,-oe)CÇoSJ

E

a20 May 74- 2L Jttl. 74

3

200

40

2

2l May 74- 12 Feb. 75

15 Jan. 75- l7 Mar. ?52

't

r.o 2.O

3

møcn dry wøight ol on individuol m9

/þ3.

shedding eggs could be deternined by assruning that significant decreases

in population densities between successive visits during recmitment were

due in part to the death of fenales that had laid their cLutch. Laboratory

cultures had suggested that females died. befoTe or soon after laying.

Sprnning their mortalities gave an estinate r¡hich could be multiplied by

clut;ch size and then egg weight to give total dry weight of eggs prod'uced

aper 0"1 ,o' f.Tubl" 6¡. One problen r,¡ith this method was the difflculty

of accounting for immature females" They may disappear fron a population

by death or by beconing ovigerous and then dying. llhen poirulation densi-ty

declinerl rapid.ly it was irnpossible to distinguish these. Therefore I

assumed that inrnatures that did. not reappear in risi-ng densiti-es of

ovigerous females died. befo¡e reaching maturi.ty. Another point is that

the size frequency d.ata ind,icates that females carried eggs j-n the lake for

1onger periods than they did in the laboratory (one ueek approxj'nately) '

llowever, any female with ful1 or enpty egg sacs uas classed- as ovigerous.

Thus the period of actual egg bearing is exaggerated by these data; large

numbers r.rith ful1 sacs lrere usually caught on only one visi"t d'uring a period

of recruit¡nent.

Table 6 also gives the initial densities of each cohort for

cornparison with the estj-nated. number of eggs produced. by their parents.

These are aluays less than the potential recruitment j-nd,icating either that

a sizeable reservoir of resting eggs is maintained or that any mortality

during the period before maxinum d.ensity in a coìrort is recorded is

comfortably accounted for. It can be seen that an important factor in

iietermining the size of the recruitment is the nunber of females survi-ving

to becone ovigerous.

The values for egg and biomass prod.ue+'ion derived. as above are

presented in Tables ? and B. On average Pi.nk is approxi'nately i;en times

more productive than Cu¡dare. Th.is refl-ects its larger population density.

In fact ure greatest prod.uction jx both lakes is fron the overwintering

rAPrE 6

The production of eggs during periods of recruitnen't in nu-inbers and dry weight ("g)

recrui-tnentperiod

Nov. 1973 - Feb.L97/+

May I97/v - JttLY I97L

Oet. I97'l¡. - þiat ]-.975

Jtne 1975 - A.ug 1975

Sep 19?5 - Nov 1975

Nov 19?3

May t974 - itrty I97L

Ðec 7974. - Feb 19?5

estinated number of ? Per 0.1 n2shedd,ing eegs (95/" confidenceli¡rits shol.m)

rs6 (úa-266)

t9s (toi-367)ls (11-31)

5.3 (z*"o-Z.o¡

3.2 (2.2-tn"L)

1,3 (1.1-1"6)

3.8 (1.9-?.6)

2.t+ (r.64.8)

dry weight (nC)

3lr"åg2 Produced

(c x 0.016 ng)

d

6/n,l

253.8

I!./+7.3

5./+

2.5

7.3

lr.6

initial C.ensitYof cohort resuli-ing (nqnbers0.1- n-¿)

85

42I/+

36L

353

l52

-clutch size(:gS/" confidence\

11ma1,s J

n'¿¡nber -:feggs produced_,(axb)0.1 n-

b ca

PÏNK

79

?o

2I./, (! 2.5) 3 r98O

15 r76i707

lr5A

336

.6(

.3(! t.5)I: 2.6)

s5.t (! 9.6)105.0 (1r0.5)

CU}TÐATE l\à-o

e

rrg.5 (!t+.s)

e recruitnent fron this generation oecurred beforesanpling began; no clutch size was neasured, bu'u itora.- assúoed. to equal the reasonably constan" valueduring 1971-1975

28/n

/+6

]-55

/r5/.

<,Ò I

1^å3T,8 7

Production of L?å9@, in Pink l¿ke ( g dry weight O'l n-2)

generation bionassproduction

egg production toial(p)

1. overrrinteri-:rggeneratlon: Nov" L973

- Aprl:.. L974

2. early sunmer generation:Dec. Lg73 - lrIar. 1)7/+

3. autunn generatlon:Apr. 1-9?4 - SeP. 19?4

4o cven¡interlng gener-ation: Jwte 197/+ 'iwrc 3-975

5. nid-su:nner generation:oc+'. I97l+ - SeP. 1975

6. nid-winter generation:JvJy 1)75 - Nov. 1975

7. spring generation:Sèp, 19?5 - Nov" 1975

210"8

o.5

5TL"7

982.2

96.2

]-:o2.3

9.9

6lt"I n/+"9

o.5

765"5

993'6

ra3.5

LO7.7

Total = ?255.6 ng 0.1 n-2

= 22"6 g {2 2 YeaTs

or 11.3 g fz Yuu"-I

-1253.8 (33/òa

U.4 ( I/")a

73 ( 7%)a

s.t, ( sfòa

2 years

-1

ins. Nov. 1973 - Nov. 197/r:

Ig23'.L rngrO.l t-2 o"!9"2 gm-

t{ov. 1974 - Nov. 1975¿

332.5 rng-OnI *-2 o"33 s rf,'

_È\\JTa

9.9

a egg production as percentage of total productio'1 (P) of cohort

lr7.

generation in I97/t, vhich had- the highest j¡j-tial densj-ties of any recorded.

Egg production is only a significant proportion of the total j.n both -l.aiçes

in the autu¡nn cohort of this year when the shrimp populations were

re-establishing after total or near total exbinction duri-ng the summer

d.rought. This is d.ue to increased survival of females to rnaturi-ty as mrch

as anything else and. perhaps to under-estimatj-on of biomass production.

(I r,¡i1l erçlai-n no::e in Chaptel I of the significance of the varying clutch

size and. numbers recmir,ed), At other ti-mes egg produetion i.s only an

insignificant pr.oportion of 'Lhe total considering the /r5'5of" error in the

prodrrction estj-mate, (ta¡te 9).

The approxinate 95/" confidence limj-ts of production (P) for eac]:

cohort were calcul-ated from the nean 95% confidence limits of d.ensity and

weight neasurements, These t!¡o errors lrere colnbined using the fornula

suggested by Brown (Char1es, East, Bror.m, Gray and Murray f97Ð in vhich:

v (P) + u2 v(w) + r^f v(r'i)

'where V = varia¡rce

N = mean populati"on densitY

W = growbh

Strictly speaking this formula should be applied to clata from

ao.Jacen¡ vl-sL¡,s and. the results sunrmed. throughout the life of a generation.

Instead, I substituted nean population density of a cohort for N and

production of a cohor'r, divided by this tËl for l'1, esti¡rating their

variances from the prevailing nean 95% confidence linits for density and

weight. Because the ljmits for density are asymmetrical (they were

derj-ved fron logs) fu¡ther refj-nement of +,he calculation of error r"ras not

vorthwlrile. The resultj;ng 95f" confj-dence 1j¡its of production

(2 J V(Ð ) are dominated by the errors il rlensi-'i;y, (tfre larger of the tvro)

demonstrating that pr:ecision in sampling the popÚ-ation deternd-nes precision

in estímating production. I have ignored any error ifl co¡rverting length to

TABLE q

Estiroates of error i¡r the calculation oÍ total producti-on (P) e4pressedas percentages and the mean biomass (E)c and. turncver ratio (PrIg) per cohort

-,4cohort nean 95/" confidence linitsof density (/")

nean 95/" confidence li¡ritsof weigh-,, (%)

t:/.

5c/r5'¡14,)

e conorcs nu:roered. as in Tables 7 and, I't-

21 excluded from rnean

approxinate 9 5f" confideneel-imits of to',,al produetiono lc7\

B (ng dry" PÆweight n-')

123lr567

/ro

PIU1q28T3l-ot5I420

/+o

116

5L/'9M))55

562T50/r94o

r57.3o.3

))n <

't?? o

24"Lr8"2

"o

32.532.46.2

13./+IT"2

1.82.Oal).+7 ./+lr.3<o¿.ô

O.50.13"r5./+r.g

,()

ctrlrÐAFE

/+5x

l=5obÒ

T2t7r_ö

10

122

lr5

6/+

20545252

¡-co(

C - - ^-t-" caicu'lated by averaging standing crop for eaeh visii;

/r9 "

weight, but it is not lilcely to be lalge because there j.s 1itt1e variation

in theÍr regressi.on (Fig. 8) 'The values for ¿rn¡:ual prod.uction vary r"ridely in Pinl< but appear to

be more constant in Cundare. T¡e tgrnover ¡atio s f /Z (latle 9) are e*ua1-ly

var.iable in botli lakes ancl perhaps indicate a l-aclc of any endogenous

regulation of cohorb productj.on if tr^Iaterst (t969) j-d'ea is correct thab

freshmter i¡vertebrates will usually exhibit ratj.os bett+een 2.5 and 5 with

a node at 3.5" llaters showecl that fol an animal with e>çonentia-l grouth,

lÍke P-e.*æ,!.æ4,, relative size of the fina] pop,':J-ation eonparecl r'¡ith the

ínitial has the greates-b effect in altering turno'uer ratÍoso Thus if ther:L¿

is any regulation of production it çou1d be through control of brj.ne shritrç

mortality, shape of the Allen curve has vj-rtua11y no j"nfluence provided

initial r,ieight is less than I-2/" of final weight, as i'b usually was'

The only aspect of procluction, neglected. so far, is loss of bionass

through moultÍng. Gecloes (rg7Ð estinated. tventy j-nstars for P'--zlej.ai.+rg

in Pink and Cutrd.are. If the i-ntegument lost represents 57i of the dry

r.reight at each moult (Da.born, 1975) then procluctíon wc'ul-d be increased by

an averag e of I5f". This is insignificarrt cornpared r¿i.th sampli.ng êrrorr

T¡ere are few values for secondary productj-on in sallrte ponds or Iaì';es

r¡ith r,¡hich my est:ï:nates can be cornpaTed. Garpela.n Qgn) cornputed' a val-ue

of 6;3 g dry weight oÏ2 yuor-l fo" ¿*a11na in the Ali'iso salt works in

san Franci-sco bay, but this r,tas only a guess basecl on mean standing crop

nultiplied by the possible nurnJ:er (8) of generations in a year according

to generatiorr ti¡nes in culture. Data for total zoopJ-ankton procluction of

iakes in temperate regions of the Nortìrern henj,,sphere e.ga Poland urith 3O^/r5

g clry ueight r-2 y"*"-1 .t* soner,¡hat irigher and less variable than ury

measurements and. appear to depenci on the clegree of eutroptry of the lakes

(ttiltUricht-Ilkowska, Gl:-;vicz and Sporlnier,rska, 1966) " The only other

esti¡nates of secondary prociuction in a 'saline lake are those of Paterson a¡d

tr^Ia1ker(tgl/,)forlqnv!arsuç-!@,abentlricchironomi.d,j.rr],ake

50.

Werorrap (f: fn northr^rest of Colac; sali-niby 36-56/".). Arurual production

(io ary welgtrt) anounted to 6/+.6 g n-2 exclusive of mortality and. first antl

second instar biomass and so is an underestimate. This l¡as only 7.9/" of

the prevailing primary producti-on yet the l-ake had. one of the Ì:-ighest rates

of secondary- production on record and L- barbitafsiç- was consid.erecl an

efficient herbivore.

Fro¡r the scant daba for prinary procltrction in Pink Lake a sj-miIar

calcu¡¡a.tion can be rnade, In this case annual seconcìary production is abou+;

40% of the amual primary production. This '¡alue is not very accurate

because the data on primary productj-on l¡ere collected for six months on1y.

Accord.ing to llilliams (personal comrmrnication) annual prinary production

is lÍ.kely to be 1or¡er and so the percentage higher. This, I thinkr indj-cates

that L"_z¿e!_ziaJfq, can¡rot be obtai-ning energy so1e1y from phytopla.nkton

because no efficiency as high as this has been recorded for aquatic

i-nvertebrates (Kozlovsþ, 1968). The only other souree of food is organic

matter, probably bacteria, in the sediments.

Therefore lhe clata in this chapter pose two questions: on vhat

do tho brine shrimp mainly feed and what causes their mortal-ity? If they

largely rely on sedinent then poor assirnilation of this probably dilute

supply of enerry could r.¡eIL result in d.eath. To i-nvestigate bo'r,h problems

I have concent::ated on measuring the rates of respiration and. ingestion in

the field"

5r"

CHAPTER ! - ResPiration of Le-@

Measurements of respj-ratory rate represent, the minimum energy intake

of an individual . Given d-ata on airir¡a1 numbers, the respiration of a

population or cohort can be calculated. this, ad.d-ed to estimates of

production, equals assinilation or the total intake of metabolisable

efteTffr

Usr.,ally the respiratory rate of aquatíc invertebrates is measured,

in the laboratory uncler controlled conditions. It is well knor'¡n that

weight of an incu-vidual and water temperature will affect rnetabolic rate"

These can easily be controlled and by choosing a number of different

combinations respiratj-on can be specified. accurately" The difficultv t+ith

such measurements is in exbrapolating them reliably to field- conditions.

There is nlounting evidence, at least for aquatic invertebrates, that other

factors such as nutritional history are equally important and' that field

acclirnation to various terupera',,ure ::egimeS in'¡aliclai;es the relation 1n the

laboratory of respiratory rate to ternperature'

Blazka (fçOe) worki-ng with natural and cultured popul.ations of

lap@ found tlús relatj-on differed betr,¡een field and laboratory a'nimalst

and in field animals at different seasons. In general, tire respì-ratory

rate,of the natural population increased much less r¿ith rising öemperature;

fron this he concl¿ded that they had acclimated .'"ore thoroughly. lle

also studied the interaction of nutrition and respiratory rate" FiÏst,

he shol¡ed that ox¡'gen consumption in the fie1d. of D-, hya-lj-nq l¡as

proportional to seston concentration in three consecutive winters' At

their lor,¡est rate of olygen consumption they could l.ast fo:: six +'o seven

weeks on body reselves. second, he found by neasuring amnonla excretion

and conparing this with o>ygen consumpticn neasured si-ruultaneously that

animals wl..,h a food surplus (the laboratory cult':re) n¡etaboli-sed no protein

while the field pop,.:1ations, r^rhich fed on louer ccncentrations of food,

52"

obtainecl between 12 and. BO% of 'uheir energ'y fron protein catabolj.sm. The

pereentage increased. ,¡ith temperature. Kersting (tgll), who also worked

r"¡ith D4lo-n!-iq (n"-*gr'-t1".), suggested that respiratory rate should be

correlated vith filtering rate because the same appendages r¡ere used. for

both functions. By measuring respiration and filtering rate simultaneously,

the latter r¡ith a coulter eountez', he was able to show this. At high

food concentrati.ons, above the rninj-mum leve1 a.t r"¡hich the filtering rate

started. to dec¡-ne, ::espi-ratory rate decreased; at loi'rer concentrations j-t

u&s nore or less constant.

To enable varj-ations in respi-ratory rate due to the above factors

to be included. in estimates of assirnilation, o4'gen consumption can be

measured. directl-y Ín the field. Duncan, Cremer and Andrer^¡ (tgZO) useA

a fielct technique to study the annual fl-uctuations in respJ-ratory rate of

rrdcro-zooplankton comnunities in two reservoirs of the lower Thames valley.

They also measured. the respiratory rate of Daplmj,A hyg.l:tna in the

laboratory at 2OoC. Using field estimates of density and r'¡ater temperature

they ertrapolated and conpared these results uith field respi-ratory rates

measured d¡ring a perj-od when UYglåna was predominant in tlie zooplanktou"

They found the pattern of changes in population respiratory rate given

þ the two rnetho,Cs was sirnilar, but the r'ield levels were always

sj.gnificantly higher perhaps because of increased activity of the daphniids

during the field measurenents. Thi-s, they suggested, r^ras due either to

disturbance from handling or to greater seoPe for active movement in the

field. respirometers (B.O.D. bottles) than in the laboratory ones

(CartesÍan divers). I¿ck of food in the dÍ-vers, but its presence j-n the

field bottles, though at concentlations lower than ambi'ent, may have had

an additiorral effeet.

I have also used a field technique for measuri-ng the respi.r"atj-on

of P, zt-etz'iana. PreviouSiy, brine shlirnp reSpi::a'uion haS onl¡r' beett

measured.for1aboratorycu1turesof@'"Usua]1ytheinvestigators

53.

(Krrenen, 19391 E1iassen, 1952; Gilchrist , 1956rI959) were interes'bed in

the effects of salinity on respiration in addition to those of body size

and temperature. A. ina r,¡as known to h¡,po-osrmole¡3r1ate and it was

thought that as salinity increased nore energy via a higher respiratory

rate would be needed. I(uenen found that respiratory ra.te increased

one and. a half times betu¡een 29%" and II6f".. ijìIiassel1, on the conl-"rary,

found a decrease betr,¡een IO/," and, 50f"" wnich uas most narlced in the naupl-iit

but wnich faded in the adults' Finally, Gilchrist coulct show no

difference in respi-ratory ra'be ai 35%" and I/rO7"". Gilchrist and

Eliassen reared their shrimp at the salinity they were to be tested

at r"¡lrile Kuenen transferred his fron 58%" to ttvo other concentrations,

neasu.ring respir.ation after twenty four hours of accli¡nati-on' Such

differences make it difficult to exbrapolate these results to the natu::a.1

habitatofeitherA'sa1inaorL-.@r^¡hereon1ygradua1changesof

salinit¡' occttr u5qally in a consistent direction" Accoldlng to

Styczynska-Jurelric z (Ig7O), changes ì-rr respiratory rate due to sal1nity

change are probably caused by physiological adaptation and d-isappear

when this ends.

l"fethod s

, The respirati.on of P. zj.eLzi3na. was neasured. in both lakes on most

visits. SÌ:rimp were enclosed i-rr 3OO m1 clear B.O.D" bo'rtles'l¡hose volume

had. been checked. and the o)rygen cc¡ncentration L'efore and after an

incubation measured using the azide nodification of the llinkler nethod

(Golterrnan, Lg69), by titrating 50 ml subsamples with standardised 0.01

N sodium thiosulphate. Variatlon in sarnple titre was uÉuaf Iy<5%.

A sinrilar proceclure was used in the fiel-d by Daborn (fgZO) for rneasuring

respiratory rates of L--Âieas., a predatory anostraca¡'

Shrimp l¡ere collected with a 2OOy zooplankton net. Imrneoiately,

the catch uas filte¡ecl through a coarse (approxiinately 1 nm) uesh

5/+.

which separated the bri¡re shrinp from the detritus and small ostracods

(platVcyptj.s) inevi',,ab1y collected. Larger organisms, that vere present

only occaslonally anrl did not pass through the rnesh, e.g. EpbEI*l-g

larvae or 4rrs!r.+þqJ]gtiÉ, were picked out llith tweezers. Jets of

filtered (particle s <2OO¡.,. ) tate water from plastic squeeze bottles

considerably quickened. the filtering. The smal-l est brine shrÍmp

(nauplii) passed through the nesh and it lras only poíisibl'e to measru'e

their respiration when there r¿as l1tt1e detritus and no ostracods"

Fj.lterecf lake water was obtained from approximately 30 cn

beneath the water surface witir a Van Dorn bottle contaj'ning a 20Or*

filter in the outlet hose. Four 8.0.D. bottles (two with and tr"¡o without

shrirnp) r¿ere fi.lle¿ for each expe¡i-nent, the first bottle fi1led being an

initial r.rater sample and the last a control. To increase the speed of

these operations, 'uhe 8"0.D. bottles v¡ere fluShed once otllyn This r'¡as

jristi-fied because the vater j-n 'bhese shallol¡ lakes r"¡as nearly ah'rays fu1ly

saturated; there r¡as rarely any sign:i.ficant cLifference be'bl¡een the oxygen

concentration of the initial and control bottle.

usually the above nanipulations, from catching the shr-irnp to

replacing then in the lake inside 8.0.D. bottles, took less than ten

roinutes, when shrimp were searce or there LfeÎe many cont,aminating organlsns

handling time j.ncreased. to a maxirmrm of tr.renty minrrtes. The B'OÓD'

bottl-es r^¡ere alr,¡ays placed upright on the bottom near the shore, usually

inside the 0.1 *2 gtl't urrised. iron cylinder to p'event disturbance try

waves, aL a depth:'60 c¡n in Pink and.<50 cm in cundare. The oxygen

content of the initial sanple was fixed irunediately after starting the

incubation.

The number of brine shrirnp used in each experiment to avoid

deplet¡-ng the inifial o4ygen concentration by more than 501%'depenclecl on

their size and the o>ç'gen content of the lJatera This was a natter of

judgement, but usually requirecl twenty to tvo hundred animals' Qbviously,

55..

the periocl of the incubation al-so affected this. Hol¡everr Ï preferred

to alter numbers of shri-mp rather than incubation tirnes. Generall;r one

experimental bottle vas incubated for half an hour and the other with the

control for one hour. A few tines incubaticri lasted two to three hou-::s"

During all incubations the shrirnp st¡an freely, but no ¡nore rapidJ.y than

seen j-n the leJrc;. Á11- short incubations r{ere nade r^¡ithin tl¡o hou¡s of

midclay. However, to determine t¡hether there were any diurnal fluctuat.ions

in respiratory ra'be f tried longer incubatic.rns of twenty four hours. l'or

these only tLrreo to six animals r¿ere used. Unfor+"una'be1y they alr,lays

gave respiratory rates about half those of the shorter incubations" Probably

thj-s was caused by inhibition from the build up of netabolic wastes and.

the effects of starvation" Instead four to five one horir incubations

spaced throughout twenty four hours were used to detect any dj-urnal

fluctuations" Water temperature was read. at the beginning and end of

all j.ncubations" ff the shrimp rvere not sr,rirnming freely at ihe endt

the e4periment was discarded.

The oxygen in the experinental and control bottles was fixed

beside the laken The shrimp did not die immediately the reagen.bs vere

add.ed, but surv.ived tralf to three quarters of an hour, presumably on o4fgcn

r"rithin thei-r tissues. Strickland and Parsons (fg68) state that al-1 the

oxygen is precipj-tated rapidly once both reagents have beeu adderl and the

bottle shaken. A1I bottles were talten to the field. stati.on for titration.

This was always done r"¡ithin five hours of collectì on and inmed j-ately after

adding the concentrated sulphuri"c acid. At the end of the titrati.ons of

the erperimental bottles the shrimp Ïtere counted, rinsed j-n freshwater, and

placed in vials in a desiccator. l,trithin a week they were d.::ied. at 6OoC

and stored over silica gel until weighed (see nethod.s, Chapter /ç) "

gccasionally a few shrirnp were lost in the overflov after adding the

reagents. These were included in the subsequent cal-culations of'respi.ration

per anÍma1. Also a few animals soraetimes ,:lied during an incubation. it

56.

Lras inpossible'to allow for these because all- the shr:lmp were dead' when

they lrere finally counted after a titration'

The filt erecl lake v¡ater u.sed in these experiments wou-l-d have

contained any phytoplankton present because only a 2OOr rnesh was used'

Du¡aligug sallryI, a.n algae reported from Pinlc, ha.s a maxinlum diameter

of ZO7. Ât fir.st to avoid the possible influence of algal photosynthesis

I used B.o.D. bottles d.arkened uith layers of black tape. llowever, I

fowrd no d.ifference in olq¡gen corrtents of the initial and control bottles

during short incubation (-2 hours) and thereafter used clear bottles'

 possible sollrce of eri'o:: trith B.o.D. bottle lespirometers

(Kamler', f966) j-s an increased orTrgen consu:nption at the start of an

incubation from Cisturbance of the animals by handling" To check thj-s

the decrease j-n olygen concentration was also nonitoreC using a Yellot'¡

Springs Instrument B'0.D. o4¡gen electrode. Three e>'-periinents were rnade,

one in the laboratory rvi-th P.-z,ig,@.4na collected from the Drxr Creelt

Salt ltrorks, Aclelaide and tr¿o at the fiel-cl station v¡ith shrimp colJ"ecbecl

a few hou-rs before in Pink Lake. Shrinp ancl filtered lake r¡ater (<?AO7*)

uere added to the B.O.D' bottle uhich was then subnergeri in a basin of

L'ater and. tenrperature and oxygen concentra'tion recorded every fifteen

¡rinutes until the animals died.. The e><perinen'u j-n the Laboratory vJ¿ìs

similar except the shrimp haci been kept in aquari-a at about 2OoC fo:: ¿r

few days. At the end of all three cxperirnents the anirials were counted

and prepared for weighing as before'

Resu-]-ts

The three experinents monitoring orygen decJine were made durS'ng

July and August 1975" llte resul-ts are in Fig' 15. Each poinf' lePresents

the respiratory rate during the fi-fteen minute interval bctl¡een reacli'tr-gs,

expresSeci aS a pelcentage of the maxirnun constan''¿ rate recorcled' From

the graph the respiratory ra-be appears nìore or l-ess constani; until an

FÏGTIRX I5

Respi-ratory rate of ?. zieíziana versÌls oxygen concentr¿¿ti-on.

Respiration is shoun as a percenta.ge of the mean constant

rate. Olrygen concentration for each value of respiratory

rate is the mean of the two readings (15 roin, apart) used to

calcul-ate this rate. The horizontal J.ine is tha average

of the points to the right of 2 ppm; the curve was fitted.

by eye.

- 305 shrirnp (0.337 mg dly wb. indiviauat-1);

lO-t3o0; ini-tial Oa concentration /v.7O ppm,

tjme to reach critical- 0a 1eve1 I.75 h;

r2o/".

- 54 shrinp (t.óOt mg dry wt. i-ndi-viAuat -1);

i-.2-I/noA; initial 0a concentration L.55 ppm,

time to reach critical 0, 1eve1 2.25 h;

135%"

a

Éo.-lPd-pv).dr-l(¡).-l(t-{

P(d

o

laboratory:

X - 8{ shrimF (O.546 ng dry wb. indiviauat-I);

t6-ZooC; initial O, concentrations 3.50 ppm;

tine to reach critical 0, 1eve1 1.00 h;.

ro6i¿"

Xo o

X a

o o o o

roo

so

oo X a

o

X

o

o

oo tx

o

X\){Joc_

Co*,o(_'O.(/)N(-

o oo

X

o

Xo

Xoa

o

2.O 3'O

concøntrction PPm

4,Or.o

o,

58.

orygen concentration of ].8-1"9 ,og fI is reached. Shortly before this

stags the shrlmp wer.e becomlng noticeabl'y less active a'nd started' to

collect near the top of the boÙtl-e. l'lhenever this crowding of shrlmp

was noticed at the end of a field j-ncubation the result uas di-scardeclt

becauso the o4¡gen coneentration subsoquently neasured LÌas about L.'l-L.g

ng fI. Never' $¡as an initlal oxygen conce¡rtration as lor¡ as this recorde'l-"

These e4perinents confj-rn that there was no increase ln

respiratory rate at the beginning of an incubatio¡r due to disturba'nce'

They also shor¡ that P.zlgtzlang is a resplratory regulator" That is

thls ani¡ra1 can naintaln a co¡rstant rata of reoplratlon r¿h1le ot{ygen

concentratfon falts untiL a crltical level ls reached' bel0u uhich the

rate drûps rapidly. fhe respíratory rate uhen consta'nt is not

signlficantly different fro¡o that neasu¡ed' for the partÍcuJ'ar combinatj-on

of weight,, tenperature and salinity in the field"

I analysed the result,s of the sholt-tellû field incubations wi'th

a step-wÍse multiple regression relatlng resplratory rato of an inclividual

(logarithn) to its nean weight (logarithm), temperature and salinrity"

The first +,vo indepencLent variables are well knowr to affeet respiratÍorr

whlle the third 1S Suspectecl of d.olng so. There were no signifícant

cllfferences betwcen regression coefflclents when the data fro¡n each lake

(60 incubations tn Pínlc, l-9 ln Cundare) were treated separately. Therefore

the dat¿ uere lumped and a single regression equation obtai:red;

1og R = -r.rr3 -l'0.002 S + 0.021 T + 0"7561o9 ll

-1 -1-L hr indivi.dualrÈtere R = resplratlon in mso, x 10

S = salinLty ín /"ø

I = ternperature in oG

W = dry weight of a,n individual- in mg x 10-3

59.

The anal-ysis of variance is gi-ven in Table 10 and the confidence limits

of ùhe regression coefficients in Table 11. Each of the three independ'ent

variabl-es accounts for a significanb par-i; of the variance in respiration

(r^,eight alone contributing SO/") and together they explain about 90% of

the total sum of squares. There were no correlations betr'¡een the

ind epend.ent variables.

Temperature varied between Ç and 2f0 and, salinity between /+9 and

2/*O%" for these e>çeri-rnents" The average QIC for thj-s tenperature range

Ls I.62 r+hi.le for a salinity inerease of 5O/"" respÍration increases by L26,

.411 the arbÍtrary length classes uere represented in these incubatious¡

although only tr^ro l¡ere mad.e in r.¡hich the tl¡o smallest length classes vere

predoninent.

Fe any partic¡lar j-ncubation shrirnp were not of all the sane length

or r.reight. This is perhaps the most serious er'r:or lntroduced into these

e4reriuentsn l.lowever, on1-y the larger of r,he tr"¡o cohorts, usually present,

was sarnplecl except occasionally when both r.¡ere of about equal strength.

Tilus the frequency distributj-on of shrimp wei-ghts in an experinent uouldt'

have been i,he sane as for a cohort i.e. rough]y normal' This clistribution

is broacer for the bigger shrimp because the variance of the mean weight

of a cohort increases as the animal,s grow, especially once sexral

dimorphism (? small.cr than d ) begins. Iogarithmic transformatj-ons of

weight and respiration largely correct this foÏ the purposes of the

regression calculations" The respiration of eggs was not neasurecl but

pregnant females were quite often present in the incubations' I asslmed

that the increase in weight from their eggs r'¡ould' arid to respiration as

equally as r¿ould a correspondi¡g increase in lreight due to growLh'

Another p::oblem is the absorption of iodine by the shrimps r¡hen

this is released on acj-dj-fication. In my experiments the amou¡t so isolated-

r¡ould. never have been large. i'he total dry r'lelght of shrinp used varied

betr.¡een 13 and. 35O ng averaglng 1OO mg. ff dry weight is 10% of uet ueight

TABLE 10

Analysis of r¡ari-ance for the m;J.tiple regression

Source of variation df Sun of squares Mean Square F Significance

weight

tenperate

salirlity

regression

residual

1

1

1

3

75

]-r.19927

o.g6l,J6

0.t*7968

12.6/+3]-r

r./+5026

0g.fl")^

( 6.8/ùa

( l.tn/")"

(s9.t%)a

LL.l..9927

o.g6/1L6

o./{7968

L-2t 1,37

o.oI93/+

579.O7

49.85

2l+"8O

?J-7.95

p(( o.oot

o\oI

a Percentage of total sum of squares

TABIE 11

Confidence linits of the regressioncoefficients

variable

wei-ght

ternperate

salinity

constant

a.756

0.021

0.002

-L.r23

b stand.ard error of b 95/" ecnîidence linits

o.o35rg 0.686 - 0.826

0.00351 o.o1/+ - 0.028

0.0001Å 0.001 - 0.003

0.11096 -1.34/+ - 4.902

O.Fo

62"

then I g wet weight or approximately I m1 of shrirnp tras present. lodirre

was only seen on the legs of the shrimp so the volume absorbed r¡oulci all,ray-s

have been less than 1 d, an insignificant amouni, l¡hen titrating 50 m1

al1quots from a total vohune of 300 rù" AJ-so if j-odine absorpti-on ldas

large then the results of incubations done on the. sa¡le d.ay should have

varied. significantly, a:nongst other things, accordi-ng to the number of

shrimp used. Such a correla+"ion lras nelrer observed-.

_ In fact, the su3cess of the regression in explaining most of the

variation in respiration indica+"es that tltis and any other effeet, srr-ch

as crowding, 1ike1y to be proportional to the mrmber of shrimp used'

(twelve to tr¡o hunrlred) r¡as not significant" This argurnent also applies

to bacterial contamination of the e>çerÍ-mental bottle. It is possibre

that bacteria arlhered to the exoskeleton of the shrimp or !¡ere excr:eted.

j-n faeces during an incubation, thus increasj.ng the arnount of o4ygen

consumed" such an effeci was probably not d.etectable r¿ith short

incubati.ons espe.cially because there r¡as rarely any significant diff-erence

between the o>rygen content of the initial and control bottles both of t¿hich

would have contained. bacteria, d.erj.ved at least partly from faeces jr.n

the sedi¡tents. Even during the twenty four hour incubations oxygen

only decreaseC in the control by a maximn of 8%. Sometj-mes a. felr ve'i:y

sna]l ostracods oï' copepods contaminated the e>çerimentaJ- bottles;

their individual respiratory rate l¡ou-l-d have been very 1on.

Before reliable estimates of population respiratj-on can be

calculated the effect of possible dir¡¡nal fluctuations in respiratory

rate associated with some endogenous rhythm of tile shrimp rnust be assessecl.

In Fig. 16 I have plotted the results of seven sets of o::e hou¡' incuba'bions

nad.e at intervals throughout twenty four hours. These sets, each cor:¡'ected

for varj-ations in rveight and ternperature, shoi.¡ that there l.¡ere no si-gnificant

diurnal fluctuations in respiratorf, Tl+vê.

FIGURT 16

Dail¡r' cotir'se of &.-aþØt@, respiratory rate measured

r¿ith t h incubatj-ons. Respiration is given as a-

percentage of the mean value measured over the twenty four

hours. Each set of readings has been corrected for

vari-ations j-n mean individual weight and ditrnal temperature

change uslng the regression coefficients. The ni-d.point

of an incubation l\ras considered. its time of d.ay.

o 2.6.75 ? rzo}, A38/",

X 23.6.75 i rzoc, r/Pf."

. o 20.'/.75 : I1oc, 135/""

+ 17.8.75 z rzoc, r2o%,

^ !5.9.75 z ]-:ïoc, 8g%"

D - r3.ro.75 z rlrac, ro5/".

À - 10.11"?5 : J:ïoc, go%,

tr

o4 00 o800

o

X

t200 tóoo 2000 24c,c

o

AX

OoAX+

AO+

A

o

+̂ú

a

\)(t(_

(_oP'õ-ØIJf_

\)cr\o(-ùo

oao

o

o

a

ao

X

+

tr

A X

roo

so

tirnø of doy hours

6/n"

The .espiraLion rate on each visit of an individua.l P.--Zie!gie4a

rnras calcril¿¡.ted fron the regressì-on equation using previous estiniates of

mean tem^oer¿rLure and sa]inity (Ohapter 2) ancl nean ueight (Cfrapter ¡i)'

Individu¿rl r;rtes uere converted to claily population rates¡ J-.ê.

mg 02 0"1 m-2,luy-l, i.¡ith the data on populaLion density (Cfrapter'3),

each coho¡b being treated. separatel¡'. Tables 12 and l-3 shoç' the da{'a

usecl and the results for each lake, which are also graphed in F:!-gures 17

anc'l 18. B.y' measur.ing the area unrler each cu::'¡e with a planimete::

the .bo¡al respi-ration per 0,1 m2 per cohort r.¡as calculated.

Discussion

The estÍmates of .Uota]- resp;i.rati-on per cohort are giv.etr ín Tab-l-e 1/+

for bo.bh l-akes, In gerreral respiration is mol.e or less proportional- to

production with some exceptions¡ êo$o generation 1 in both lakes,

resulting frora rapld.ly rising salinity and ternperature or improved sprvival

of tjre shri-npjio heavier i.reightso Âs r¡ith the vaL-u-es for cohort produc'cion

the largest so*rce of error in these respiration rates is the /no-5)it" error

in measuring population d.ensity. The error in predicting respiratory

rate per inclividual fron the regressj-on equation 1s rnuch s:nalIer' (s-15Í) t

ancl errors in the ind.ependent variables, particularly mean weight of an

individual and mean tenperaturer are unlikely to increase it' iSecause

the larger error r,rill- clonúnate any cal-culation of the conbined error',

as shovrn in Chapter d, I have assuined that the probable error f<¡r values

of cohort respiration is /+O-5O"/". Any error f1c¡n calculatlng total

respi.ration by integrating a series of daily v'alueB r¿iIl be small"

phillipson (fgZO) found that an estj,nate of annual resp5-ration calc*lated

by rmùtipJ-ying mean annual respiratory rate per ru:it weight by mean annual

biomass r.¡as usually r.rithin 5% of that from a det,ailecl a'alysis of the o>rygen

consumption of the various U-fe stages'

Ït is possible tc calcul-ate the assinila'r;ion ra-bes for each cohort

65,.

TABT,]T 12

Calculation of daily rcspi::a'r'ion of the P" ¿iet-zianapop"fãtion in Pinlc Lake, using-the regression equ-eition

ärra pop"fation densities from Chapl'er 3

emÞ- mean dry weigh'r,(oC) or inclivicLual

in cohortspresent (mg)

ng O"x 1O-3 mB Or O.l- m

hr-f indiv dai-I--lt-dua.1 *

67.t386.28

0 "133r.930.28

20"59o "L7o"5gO.3/1.0.08

39.vlv7/+"37/+2./vBr8-9356.6618.850,03

16"?-50.03

16"61

ba

date

l-3.'rI.'/313"r2.73

16 "'r.'l /+

l-5.2.7 /+

]-'I.3.7 /+ôô t 4t1á'o4o I t*

láolol4

18,10.74

l.2.I)-.7/+

]-.I.]-2.7/+

l3.r.75

rr.2.75

16"3.75

r.6.75

22.6.'1520.7 .7 5

r'/.8"75

16,9.75

19.ro.75

8.1r.75

sali-nitY(/" )

amean teratr.:.re

rlu6162

2/"O2].6

178

209

510

1v0

1B23

23

22

23I7

o"758T.I330.09c1.810o,o2/r,1.0880.0062.29O1.208

.4r

.o7tÔo4.a

,/*7(o

. rr.5ga.23

2L.6910.17L.453.597.60O./+2/+.78

o.o92É .tl

e).1/.þ,6"7 /*

23L6

I5I1.60

138

94.

o<

102

107

120

r39

t38

)-/no]-35

r20

89

105

9O

o"5goL.BzLo,o/+o1.060O.3/+9o "3230.016a J6/,0.007o./16r0.051O.5/rB0.01/+r.o3g0.050r.309a,o5/+r.875o.3r70"685r.977o.o1l+I.2T30.121.o.3590.005r.4630.0211.793O.TA2

.ub

.92

.20

11

"57

T310

11

L5

T6

18

22

23

18

12

a

210a-

0?

0

))

.o2

1111

/v.28Q.2'/7.750.?81.gr0.717.'122.013./-,-77 "550.185.360,gL2.1-l+0.086.C.7.1.

c),335.340,80F: "37O¡ /Ð7 "592.37)_.297.96¿" )ö- ÉlKo )/*0.00r.L/+i.962.lr]O

"Oui2"OL0.gB0.1,40.70

T3

T6

t6

1B

6627o4L7

a calcul-ated. fr.om monthly readil)gs averaged uith adjacent maxina anC

minima

b inclu.des l,¡eigh'b of egg sacs of pregnant I

lA3rE 13

calculation of daily respiration of the P= zietzi-a+a population in lake cundare,

using the regressioi uqlràtiott and pop'alation densiiies from ChapLer 3

date salin1tY (% ) temp(oc)^

18

2323T3

11

11

nean eratureÊ mean d.ry weight ofoindividual i-n cohortspresent (mg)

¡rE 0indi

-¡ I l^l

vaciual

2.868.094"6r8"L39.8/uo.Lgg.r2o.2r7"08O.9/*1.892.38/+.a58.17

IA.25o "765.880.18

3 ir"-I -2mB0c0r1n--- -toay *

u.rr.73

u.rz.73]7.1.'7/+2L-5 -7/+

17.6.71.

2L.7.7/+

!5.LJ.7/n'r3.ïi.7/+]-3.L2.7/+]-5.L.75L2.2.75

17.3,75

98

u22]-5119

I3I

92

/rg546689

L33

].99

0./*38r.737o.456A.6,!52"'Ì250.0522.6020.0182.3"1Oo.lá4o./+L6o "/oB3o"195r"636!oOl:)0.c5/+o.5030.005

'7.O73.88

'1 Q ÃO

3.321.?10.04o "77r.430 "o/+??o

1.olu1.312.3L/*.U7

clÂL7192020

2T

o.c}.a

2.16o.B4Ê n(\

0.01

a calcul-ated. fro* nonthly read.ings ave"a-ged. r.rith adjaeent ¡aaxima and rninj-na

b j-ncluô.es weigirt of egg se.cs of pregnant I

c actual popula.bion d-ensity too lol¡ because of sanrpiing error; instead' average

of densities in llovernber ano Decembet i9V/+ used for calculation

FTGTTùE 17

Monthly variation in the daÍly respiratory rate

of the P, zi€.tziana population in Pínk Lake.

Nr:nbers refer to the generations described in

Chapter /"e" Ârea under eaeh curl-e estl¡nates

total respirati-on- 0.1 t-2 of a cohort.

72

3

4

sot->.o

!a\¡.E

oNo

cr\t

t974t973

Lr.f

5 6

t97s

FIGURE_IJ.

Monthl-y variatlon in the daily respiratory rate of the

D 7,1 AnA pcpulation j.n Lake Cunda.re (Numbers as before)

roT>ov

c\l,E-o

5

C\¡

ogìE

2

4

3

t975t97 4t97 3

69.

TABLE 1¿

-Total respiration of the various generatÍons 1n

Pink and Cwrd'are

generation ng 0, 0.1 -2n

PINK

1. Overwintering generati-on:Nov. 1973 - Apr. I97/+

2" Early sunmer generation:Dec. i773 - t'Iar" I97/+

3" Autunn generetion:Apr. l-971 - Sep. 1974

4. Oven¡intering generation:J¡;6,e L)7+ - June 1975

5. Mid-sr:runer generation:Oet. 1974.- Sept. 1975

6. I'fid-winter generation:Jt:Jy 1975 - Nov. 1975

J. Spring generation:Sept. lr975 - Nov. L975

1, Mial-winter generation:Nov. 1973 - Feb. 1974

2. Renai¡rs of overr,¡ínteri::ggeneration: Nov. L973 -Dec. 1973

3. Autu¡rn generetion:lûay I97/+ - JttLY L97/+

4. Oven¿i¡terÍng generation:May 1974 - Feb. 1975

'5. I'aLe sulumer generatlon:Jan. 1975 - }iø;r. 1975

/+158.0 Total = L8372.9 _ -2 ^ -J-ng 02 0.1 n - 2 Yea::s -'

77OI.2 = 183729"4^

^g'Or'^-2 2 Y"ut'-l

906.0 or' 9L86tr"5 nE oz*-2Yuu"-l

qTINDARE

5209.7

27,-8

336.5

33.7

8L2.8

7L.2

60.8

555"3

l/*8.8

Total = !649.8 DE 0,, 0.1 n-2l-6 nonths-I'

= I6l+9o"a ng o" to

t6 months-l '-

l-:2367.5 nc oz ttr-2 yerr"')-

-2

or

70"

by suruni-ng data frorn this and the 1-ast chapter. This r¿iL1 be postponecl

unti-l chapter B r,¡hen all the data is converted to ener:gy units' I{er'e

ï uill only dlscuss the poSsible ecological sÍgnificance of some of

respiratory characteristj-cs of thi's animal'

The respiratory rate of individuaf !'.-+ig!'z'ia4q is the same order

of magnitud-e as that predj-cted from Zeuthenrs (fgZO) p1o.b of 1og respilation

agairrst 1-og body weight for poikilotherms, The range in values is very

si¡nilgr to that found by Gilchrist (1956 , L959) for A-r-S-alj¿q: 0'9 to

-'l individual-l fo, a change in dry weight from o.o5 to 0",1r4.0 mg Ot hr '*

ng a.t 25oC anð. 35 or I/*O%.. Over the same change in weight at 25oC ancl

I/*O%" the respiration of P. zii-tzi4lq rises from O'9 to lv'6 rng 0, hr-I

individual-1; at' 35/", the range is onJ-y 0'6 Lo 2'B'

Gilchrist (195Ð did, not clain that A" -saljtna l¡as a respiratory

regulator, but she did. shcw ttrat o{ygen consu:nptlon decreased t¡ith o}rygen

concentration below 2.3 mg O, 1-1' This is hi-gher than the critical

1eve1of1.6-1.9n8oz1-1found.fol"P@,butGi1christl¡as

unable to monitor oxygen d.ecline continuously and' hacl to rely on a serj-es

of short incubations fron various initial o4ygen levels' Mj-tchel-l (]rçl:)

studied the respi-ration of both brine shrinrps and by follouing o4fgen

dec1iner,¡ithanO5e1ectrode,asIdid.'shor.¡edlhaL?@regu1ated.

its õonsuuiptiorr down to 1.?-1.9 nE OZ1-1 and &-salina to 1'1 me 0a 1-1

at 2OoC and at salinities between 75 and.260%.. The critical leve1 for

A. salina increased to about 1'9 ng O, t-t r¡hen tlreir haemoglobin r'¡as

removed. According to Geddes (L975 a) p' zi&1lz'i¿na' does not contaÍtl

iaenoglobin.

Neither Mltchell nor I (tig. 15) vere a'b1e to shou any sj-gnificant

variation in the critical Ievel for P' zietziq!ÉL L¡ith salinityn temperature

or mean dry weight of an j-ndj-vidua1. By keeping the critical IeveI constant

at a .1ow

o)qrgen conce¡tration !-4þ[z[ana main'',eins a steady supply of

energy.'anappropria.i;ead.aptationr+heno)çygenievelsfalldueto:.ising

7L"

salinity or temperatu-r.e. The iowest o4ygen eoncentratj-on recorded in

either lake during this study vas 2"2 mg 02 1-f- ( 27oC, z/,'OY"') iu pint

Lake when ther.e were very few shrimp. Lor¡er o{ygen levels can only be

reached in welt mixed l.alçes by increasing the salinity beyond z/+O''f"".

This wÍI1 ki1I f,he shrimp through salinity stress. before oxygen sitortage

occu]îS (Geades :-:9?5 a). Thus oxygen concentrat'j'ons lower than the critical

Ieve1 are not 1ikely to affect the populations studied'

-'Thereisnoevic1encetosugges*"p-'-Mcanrespireanaerobica11y"As indicated, shrirnp in the experimenl,al botttes died within half an hour

of the oxygen being fixed. ltrhen usirrg the o4ygen electrocle the shrinp

died at very lolt olygell tensions' In general, acclimaLion to low

o),îrgen concentrations favours regul.ation of consumption dor'¡n to lot¡

concentrations in aquatic invertebrates (Prosser and Brot¡n, 1961) '

The regression coefficient of the independent variable weight

has often been determineci-. It should lie betlveen 1.OO (respiration

pr,oportional to weight) and 0.66 (r'espiration proportional to sui'face

area). Zeuthen (fgZO) quotes a value of O.8O for crustacea, which is

not significantly different from my value of O.76" Zeuthen points o'rt

that this value can change r¡ith the developrnental stage of the animal atrd

incleetl Eliassen (nfZ) showed that !. galina has a 'a1ue

of 1'00 betv¡een

body sizes eontai-ning 1to 10 g N (abou'b o.o1 to 0.1 rng dry weisht), but

a value of 0.75 below this range and O.óO above it. Gilchrist (l-956t 1-959)

over a size range of o.o! to 0.4 mg dry weight found a coefficient of 0'66

for females at salinitie s of 35 anð. I4O/"" and. nales aL I/þ0/"" but a'

.significantJ-y higher figure of 0.BB for males aL 35!"". she showed that

this r¡as du.e to the more rapid increase in area of the second antemae

oftherna]-esat35%"comparedwit'hI4o/"".Simi.j-arvarj.ationsloayoccur

in the coefficient, for l, zietz,i+nq, but by only fitting one line to the

data, these are ol¡scured. As ah'eacly nentioned, this error and any error

in basing ny coefficienl, on the rnean weight of the range of sizes in each

incubation were insignificant in calculating population respiratory losses'

"Ì2n

The sarne applies to the val-ue for [O of 1'62" The regressÍ'on'

v¡hich covered long tern rathel than short term changes, obscured' any

variations in this val.ue r,rith temperature regirne or bod;' size' Despite

this because it is lower than Q.,Os of 2'2 t'o 3'5 from Kroghrs widely

quoted. curve for temperat,re correcLion of respila-bion (r'Jin5erg, L97l),

it suggests that P_-r-3tg:þliiÆ. accl-imates to grad.ual1.y rising temperatures'

This is obvi.ously adaptative in maintai-ning a InoTe s'ùead'y r:espira'tion

rate over the v¡1de diurnal fluctua;ions in tenperatule soneti-mes

enco'nterecl, (BoC o:: more in summer'). The lack of any cii'r'al

enclogei-ious rhytþn affecti..ng respiration of P-"--*!ziw. inciicates there

were no respi-ratory or feeding cycles and tha.i; inthe shoi"t term e'g"

the d.uratj.on of one of my vi-sits, metabolj.c rate of the population

could. be consi-cì-erecl constant.

of the inclependent varÍables in the regression, variatíons in

ueight,, because they contr:lbute most Ùo the expl.ained srun of squ'ares,

cau,se the greai;est change in respiratory rate" salinity varj-ations ha've

the least effect. The sarne rate of increase r,¡ith salinity is fonnd in

both lakes, alt,hough the aveIage salinity is lor'¡er in cundare' llhis

rate of increase is also the same as that found by Kuenen (1939) r'r¡ren

he compared respiratory rates of &- salina, culturecl at' 5B%' r¿ith those

twenty four hours after transferring the shrimp t'o 29/"' and !!6%'" "

Styczynska-Jurevric z (tglO) proposed that metabol.ic changes cl'ue to

salinity varj-ation are causerl by physiologica]- aCaptation and disappear

when this encls. This does not seem to apply in my case because

significant increase in respiration occurred r.¡ith only a slou rise in

sali-nity. such a slow rise presurnably requ-ires little enerry fcr

physiological adaptation. The simplest e4planation is, of couf'se, that

¡nore energy is needed for osmo-regulation as salinity increases"

Gllchrist (f956) was unaL,1e to show an increa..se for &-g}&,n obtain:i'ng

the same respiratory rate at 35%" anð, IA.O%". Perhaps r;his discrepancy

'13 "

results from my measurements beíng taken on a v¡ild. population subject to

varying salinity vhereas Gilchristrs were rnade on cultured populaticrrs

at constant salinity tuhose nutrj-tional history and thus netabolic rate

can be expected to be significantly different (Blazka, f966) ' The

regression,natut.ally,doesnotprovebiratsalinitycausesthechange

in respira-bion.

I shor^¡ed at the end of the last chap'ter that it was unlikely

that P.,2.,-ie!-zj,qÐg could obtain a1i its energy fr-on primary production

alone. Ass1ni1ation rates (to ue given in the final chapter) prove

this because they exc.eed primary product-i-on by abouÙ three times'

Therefore the shrimp must depend on orgauic matter¡ êr$' ba'cteria, in

the sediments for most of their eneIg'y. Dlring the incubati-ons the

shrinp l¡ou1cl have been able to i-ngest any phyto¡rlankton ol: sllspended' nud

particles enclosed in the bottles. Although the amounts of these appea'red

snalI, it is unlikely ihat food shortage had' a significant effect during

short incubat:ions. The guts of the shÏimp usually remained full' of ¡rud

suggesting that the energy of digestion was included"

Decrease of respiration rate at high food concentration, as shovrn

by Kerstine Ogli) for D-ephn:i'a, would not apply to these experitnents

because of the low particl-e concentration in the bottles' It could

OCCur r.rhen P. z'ieLz na feeds on the sedimen'r' surface of the lake"

Ilor¡er¡er, observation indicated no obvious decline in the rate at which

shrimp on the bottom beat their legs'

7l+"

CHAPTER ó - Energy content of lalce sedimerrts

Tntroduetion

To complete an energy budget for P-o--zie!-ziQllq- measnrements alte

needed of its rate of energy intake. sedimen'bs rather than pÌrytoplankton

provide most of this input (chap+'er 5)' Therefore energy intake cair be

calculated. fron the dry weight of nud eaten per unÍt time and its e¡elg¡

or cal-otic content. This chapter deals with caloric content'

The organic composition of sedj.nents of Australian saline lakes

is poorly knoÌ.rn. The only study is that 6f Timms (lglA) l¡ho measured

the organÍc content of sedj¡nents from vari-ous depths in lakes Gnotuk

(salinity 59%ò and Bullen¡aerri (S/,.) (approxirnately 35 kn l^l of Colac),

inclucling estimates of percentage carbon and nitrogen' Nothing is knor'ni

about the halophj.lic bacterj-a and other micro-organj'sms present in the

organic flactir¡n.

l.lorth American stud.ies of particular note a::e those of Eardley

(fçl8) arrcl Bennett (19ó2). Eardleyrs work is especially relevant because

it concerns ure sediments of the Great Salt Lake, Utah, rqhere Â" ':4Ji--49

is abunciant. He distinguished three t¡pes of sedlmen-b: clays, oolites

and calcareous a1ga1 sediments. clayS \.Iere commonest and ranged fron

fine black sulphurous clay to sandy clay 1-oarn, /*5/" of their dry weight

being carbonate. Bacteria vere found in all clays and Protozca in a

fetqnTheblacksulphuroussrrrfaceclayhaclahiglrer.organicconteirt

than underlying cl-ay and generally had the highest content r¡f al-l sedinents'

Arterniid faecal pellets ltere conmon. Eardle¡' estimated ihat t'hey

consti-buLed 3I% of t¡e total nurnber of sedimen'b partlcles and' found they

had the sane organj-c content as the clays, but a higher carbonate content

of 77%. He concl.uded 'Lhat A. salina ingested much sediment and that

faeces vere a najor source of sediment. This was contrary to ea¡'lier

75"

supsestions that A. -¡rlj4.a fed only on algae.

The sectjments in Pink and Crurdare are cla.ys (according to Eari11-eyrs

classj-fication) more or less homogeneously clistributecl; oolites have not

been noted and calcareous algaI deposits are absent. Faecal pellets frour

P" zi 21ãna ale cortlnon and neasure ^'C) .1 by 0. 3-l .0 mm. The blackest

and loosest sedilients occur in Pink, those in Cundare are firtner and'

lighter in colo'"rr.

l'lethodg

Ì'Íud sarnples l¡ere taken monthly from June to l'lovembet 1975 i-n Pink

Lake directly from the top 3 cm of the sediments by drawing a gl-ass jar

along the surface; only surface mud j-s available to the shrimp' Vertic¿tl

variati-on in caloric content is not d.ealt r^rith althou-gh this p::obably occuns

(cf . Earclley, 1938). Generally, sanples r,¡ere taken al^ray froru the shore

in places r¡here there Nas no undecayed or partially d'ecayed organic

detritus overlying the sediments.

All the samples, except those taken j.n Oc'bober ancl November, u'ele

u¡ashed with freshwater (x4. ) within a few hours of collection. They were

then stored over silica ge1 until they t';ere dried' (within a r'reek of

collectj.on) at 1O5oC for at least twenty four hours. Dried samples r+ere

ground to a powd-er and stored in desiccators for up to five months before

analysis.

The calor.ic content of 2OO-300 mg from each sarnple l¡as rneasured-

r¡ith the wet ox-idabi-on technique of Hughes (rgzc) ' This avoids

.endothermic deco¡nposition of carbonate which occurs in bornb calori'metry

(paine f96/). Control samples (5OO mg) of organic free sediment account

for any interference by inorganÍc material. Calorj-c content is calculated'

by multiplying the diffel:ence between the titres of the control and

enperj-noental samples by the calories released l¡hen o)Vgen is used- to burn

organic matter¡ i.êo 3"38 caT mg-1 oz'

76"

organic free sedi¡nent and estÍnates of percent Snorganic matter

r¡ere obtained by burni-ng 0.5 to 2.0 g of cl'ry, uashed' or ururashed, sedlment

at 55OoC in a muffle furnace for two to three hours" At this tenperattrre

sone carbonate in addition to organic xnattor also deconposes' Thls r¡as

conpensatecl for by decreasing weight losses by 3.7f"t a value derived þ

comparing the percentage loss of paired samples, àt" of vhich ha¿ been

treated r^rith 2 N sulphurÍc acid to drlve off 'Lht¡ carbonate' llater of

hydratlon, lost at¡ 55OoC, was reintroduced af'l'er an ignitlo" y rewett'i'ng

the sanples and drying at 1O5oC for twenty four hours'

It was also necessary tO aCcOi¡¡rt for organlc material leachecl

while vashÍng the sediment. The exbent of this was evaluated by coupari'ng

the calorfc value of five santples (¡ tf :aeh) from washed ancl five fron

unwashedmud.tod'eterminewhetheranyorgsnfcnaterialwaslclstfrorna

sedixûent sanple before it, was d.rlod e.g. þ baet,erj-al respirationo the

caroric values of tr,¡o halves of a sample uere measured, one dried

fmmecliately after collectlon at 80o*9Oo for eÍghteen hor:rs, the other

stored over silica ge1.

Theca1ori.eva1ueofPJ.j@faeces,eo]-1ecteddur,ingexpei..inerr|s

described Ín +,he nexü chapter, uas also measured as lÍere a fev nud sanples

taken in cundare durlng Nove¡nber Lg75. Finally the organlc nitrogen

of sanples taken in Pink fron June to october t€s deternlnecl víth the

Kjeldahl method of Ì.lajor, Da1 Pont, Klye and' Newell (tglZ).

Resul@

Table15glvesestinatesofthepercent.ageínorgani.cnaterial

in sampl-es. These are essential for correctíng the titre of the control

flask ln the r¡et orj-datlon to that clue tc¡ the snaller ueight of i'norganic

materlal in the oxperinental flask"

There was no d.ifference between the cal0ric colrtent of the two

halves of the nud sanple, one dried lnnedlaüely (11?.8 *r g-1) and the

other drleit l-ater (ttS.g cat g-1), md thus no appreci'able loss of organic

77.

TABLE 1Ã

The percentage of inorganic rnaterial in sedj'ment,urnpi"s from pink Lake. The mo.ths of collectionare in brackets. Faecal sanples included some

from Lake Cundare. The mean percentages uerecalculated fro¡l angular transforrnation of tbeoriginal Pereentages

No, of samPlesburnt

mean percentageand range

TJashed nud(lune to October 1975)

Unr.¡ashed mud.(octouer and Novernber 1975)

go.3 (88. /+-9L.8)

88.2 (86.5-89.5)

92,6 (9o.5-9/r"5)

/+6

L3

Faeces(November l.)7 l+-Jayuary 197 5;June-August 1)'15) 16

78.

matter flom sarnples before analysis. There was, hollever, a signj-ficant

leacþing of organics when r.,ashing the samples (taUle 16). In l-pth

experiments to best this, an average of 26.A.% of the organÍ-c mattel j-n

the unwashed. sarnple was leached by r+ashing. There was little varj.a'bion

betr^reen the e>çeriments, although r.rashing tras apparently more effectj-ve

in October because bhere is a significant difference (0.05>p>'0.02)

betwcen the rnean dry r,reights of the washed. all-quots. These results

indicate that solubtre organic nraterial in the sediment (the rnost::eadil-y

leached.) does not form a najor fracti-on of to¡al calores.

According to llughes (fgZO) only 80/" of the proteirrs are oxidised

by this uet oxidation. Thus 7.1 cal ng-} Kje1.dahl nitrogen should be

added to we¿ or<idatj-on vaL.ues assurning that protein has a caloric val-ue

of 5.65 ca;' *g-1 rnd 11af 16/" of protein exists as Kjeldahl nit¡ogen.

The concentratj.on of nitrcgcn per sample and the corrections appliecl are

given in Tab1.e 1?; only r.rashed sa.mples l.rere anal-¡rsed-. As tÌre percenta.ge

of the total calories in a mucl saraple represented by the correctiotr is

fairl.y stabl-e the mean value of '7.5% was used 'Lo correct the caloric

value of those samples, washed or unr,¡ashed, whoSe nitrogen cont'ent t+as

not measured. All correc-bions for unoxj-d.ised pro'bein were applied befcre

accounting for leaching.

/ The final corrected. caloric vahres for uashecl ¡uurL are graphed

in Fig. 19. They are shor.¡n as logarithns to enphasise Ïelative changes

in the concentrabion of organi-c matter, assumi-ng this is pz'oportional to

the density of micro-organisms. The presence of bacteria r¡as confirmed

by culture of inocula from wet sediment samples. Sone of the samples

taken in October and, Itrovember \,rere unt¡rasired., and thus needed correction

for their larger inorganie content" This rvas calculaied by subtracbíirg

from the weight of qnr¡ashed sarnpl-es (fa¡te L6) +,L^,e weight of organic

naterial, estlnated. using the mean ca.l-oric value for aquatic detr:itus:

5.I7 ca:J. mg-l ash-free dry veight. (curnnins and lfuychecl:, 1971).

TABTE 16

4eriiûents -t o determj-ne the effect of washingc content of ihe r¡ashed. sedi¡nents used 1n the; -,,he value used is i;hat for snaal (?-5O 1)

All caloric con'tents have been correc't'ed for

bleaehinge4periment

r^rashed nud.

unr¡ashed. ¡irud

r¡ashed mud

unwashed. mud.

rnean clry weight (ng) of5 rnJ- alicluots of r.¡eisarnple

rl*za.roa

196B.7/+

!6?c.834

rgu.55

caloric conten',, inca].or]-es tr. riryweight of sedineni

r7lr.8

r73.3

!63./*

L82.9

totai calories irt5 ml aliquot

¿-/+ó. ¿

3LT.I

¿O4.aö

355.7

7o Leachea,

27.2

25.5

0ctoberr975

(ì(

ltrcver¿berr975

(

(

-l\oo

mean weigh-t of uashed nud significantly diÍferent (p<o.oo1) fron that of unwashed raud'é

b average perceni; leached. = 26"/+

TÁBLE 17

Nitrogen contents of wâshed rnud. samples and 'r,he correcÌ;i-ons applied. to uet oxidationvalueõ for the 20% wrcrtdised protein. The mean percentage of the total calories ina mud. sanple representecl by the correcti-ons r¿as calculated from angular transfororation.

d.ai;e ofsanplecollection

rng r,r g-1 dry sedirnen (")" "?äîïr+:ï"":rflfi *;:ffiffi')ni-trogen

ca-lories from correctionsas /, of futa1 calories j-n

mud

!.6.75

22.6.'.l 5

2L.7 "75

18.8"75

13,9.75

rr.Lo.75

2.5

1oö

L.7

r.6!.lrno

2.0ìçt

l-7.6

20.0

12.\

11.0i0.1

6.r

Ilr.I12.I

7"7

8.1

6.0

9.57.9

Þ.ö

7.5l.ó

mean%=7.5!O.65(95/, contidenee1in-its)

b

b

oooa

(

i

b ana1,u:ses fron two d.iffei'ent sa.nples in Oc+rober; analyses fro¡o onesample in August

C r"*., = 1.8 mg N g-1 d.ry,"rashed. mud (95d/" contidence lir¿its, 10.5)

FIGURE 19

Monthly variation of the nean ( o ) caloric value of r.rashed

mud from Pink Lake. The first sanple j-n June and those

in October and November were taken off the r¡est shore, the

others off the east shore. Snal-L dots represent individual

sanples

A - sanples fron Lake Cundare taken off the north

and south shores, the higher value for the south

s¿mp1e.

o - P. zietziana faeces

40c

locU=(-cì!

t-EU

¡

A

a

aa

JUN JUL AUG

t975

SEP ocT NOV f aeca,s

82.

Included in Fig. 19 are some r.alues for mud from Lalce Cunclare ancì'

faeces from both lakes" Only two 5¿rnFles of faeces ruere oxidised, one

collected. cluring the septemljel. vj-sj.t to Pink, the other cotnposed of sarrples

collected in pinlc and Cundare betueen Noventber I97/+ ancl JanuarÏ 1975 and in

Pink between Jwte and Âugust 1975"

Di s'ì on

Generally the caloric value of sedimeltt from Pink Lake was stable;

the fluctuations plobably retrllesent spatial heterogeneity" There r¡Iel'e no

significarrt differences bef.!¡'^en the r.ieans of samples from the las-b tirree

months of coll-ection tested r¡ith Solcal. and tl-ohlf's (fç69) rnodified t-test

fcr use with unequal varj-ances" The no¿n value of all samp1es is 211-'1

! LO.4 (95% contirlence lirnits) "u1 g-1 dry lrashed mlrdn The calolic val*e

of mud from cundare uas less than this while that of the faeces was

somel¡hat higher. Marine sedinents analysecì by Hughes (rçzo) contained

-¡about 6/+ ca]- g i dtr seCirnenÌ;; rnud fr-om La-ke Ontario (Toronto harbour)

containecl 220-2L8 "aI g-1 (Brinkhurs'b, Chua, Kat'Lshik, ]rgl2) '

Themeanclryweightoforganicnabterinasamplecanbeestj.rnatecl

by convertin¿ tþe average caloric content to milligrams usinßr as hefore,

the factor 5.I"/ cal rg-1 dry wei.ght. This glves /u0.8 mg of organic matter'

per graru dry veight of washed mucì., i.e. /ç.IÍo organic rnatter, whích reduces

+,o 3"3% for unwashed mud because of the increase in itrorganj-c content

(fa¡te t6). The average nitrogen content (faUfe 1?) is equì-val-e^t to

O.Ly% of the dry washed sediment. Assuming that this is derived ruainly

from bacterial protein as Neve11 (D65) shoued for mari¡re seclimen+v, and that

nitrogen represenl s 15% of the dry rueight of a bacterir¡n (Altnan an¿

Dittrner, 1g1/+) then there are 12.0 mg bacteria g-1 d"y mud constitu+'ing

29% of the total organj.cs. The rest is pcssibly non-1ivi-ng crga:ric

naterial.

83.

Tho organic content of the untreatecl nud is comparable t'o the

leve1s of 0. 5 'l,o 2.2/, Eardley (fg¡S) found for the clay seclinents j:r the

Great Salt l¿.ke, Utah and to those of 2 to "l/, Bennetf (1962) recorded froro

various sal-ine lakes in Hashington S'bate. Tiumst (f9?6) values for

the ¡nrd.s of l-akes G¡otuk and. Br.úlenmerrí, 2/+.I anð' 2O'I/" respectively' are

muctr higher as is hls mea¡r nitrogen content of A.75/,. In Rybakrs

(fg6g) attenpt to classif}' the deg'ee of eutrophy of Polísh lakes

according to the organí,c content of their muds, those'øith values of

LI.Ú" tß ?O.O/" were considerecL oligotrophic"

usually the value of percentage organic rnatter is estlnated

directly fron the weight, loss of sampl-es Ígniteil in a nuffle furnace"

However, tho r¡alues (TaUle L5) found by thls nethod', 9"1 and l-1'B% for

nashed and. rrnr¡aShed. nrud respectively, are higber than thoso derived' fro¡n

the wet oxidation ueasurenents. Ttre discrepancy perhaps arlses fro¡r

lnconplete reconstltution of the uater of hyd.ration (zuetney, personal

comnunication) after ignitlon or üoro decornposition of carbonato tltan

estiroated in tests of this. The Latter is less likely because of the

consta¡t anount of deconpositlon from this source (see above). Howevor,

even lf the error ls in u¡rderestinating the percentage of inorganlc

naterfal, there wouLd have been no slgnificant effect on ealculations

of caLoric content; if 100% ínorganlc content had been assumed, the

lnterference in the titre wor:ld have been snall compared rrith the titre

due to the od-d'ation of the organic fraction'

Because of the above difftcul-ties, percentage organic mat'ter is

more reliabS-y esti.nated from the l¡et oxitlation' The on3-y ctisadvantage

vÍth this rnethod is that lt o>d-dises aII carbohydrates a:rd. fats, but only

8O/" of the proteins (Hughes, 19?0). He found that the calorÍc vr¿l-ire for

bovine albunín (z*.g tcal g-1¡ out ined by wet o:d.dation was lower than

that (5.g lccal g-1¡ fror standard bonb-ca1or¡netry. However, Kersting

(DZZ) has pointed. out that the end products of protein oxioatlon in a

8/*.

bonb-calorimeter are different frorn those of an͡na1 metabolism and.,

possibly, fron those in a wet o.xidation" Ho showed that N, tlms the

nain end product Ln a bomb whereas in aquatic invertebrates, at leastt

ít uas NH, and, that a correction of -5.9 "aI tg-l had' to be applled'

for this non-biological oxidatiorr of NH, to Nr. . trf the end' product

of r¡et oxldatíon of protein ls also I'Iþr a possÍbility because the

oxidation proceclure is sÍ:nilar to that of Kjeldahl digestion which

converts proteins to amonia, then applying Kerstj-ngls correction

Lowers Hughes t valuo of 5.8 kcal g-1 by bonÞcalorirnetry t'o 4,9 kcal g-1.

T¡1s is very close to his value from r¿et-oxÍdation. Nevertheless,

as the end products of thts oxidation are sti11 not clear, his corree,tion

has been retained; it r¡as only an average increase of 8/" for the sampl-es.

Fínally, it is significant that the caloric vaLue of the faeces

Ís about 36/" higner than the mean value for the u'd. It suggests that

p. zl.ebziana feeds on the sed͡nents by selectlvely furgestfng particles

of high organì-c content. Brlnkhurst, Chua and l{aushík (1972) shor¡ed

the sa¡re for three benthic tubificicl Oligochaetes frorn Toronto harbour"

In their case the caloric rralue of the faeces vas 25/" h"igher than that of

the nud, the Cligoetraetest onJ.y source of enerry'

85.

CHAFTER ? - Ingestion and eges';ion by P. ziet?-iarla

Introduction

With clata on seclineltt caloric values it is not,r possible to

calculate the energy input to the population of P. zi.et'zianq from estimates

of their rate of mud ingestion. This rate was measure,f dj-rectly in ',,he

fie1d, again, to avoid exfrapolation from laboratory data. Tenperaturet

and body size rui11 affect ingesti-on ::ate; for filter feeding arrinal-s food

concentration ancl its size and. chemical composition are also najor

i.nf1u-ences (i{aney, ].77I) " Er- zi-*rang is a filter feecler, but r^'hen

ingesting sediments rather tha:r suspended particles food concentrati-on

is unlikely to be limiting.

Nurnerous nethods have been used to measrrre ingestion rates and

assimllation efficiencies (Klekowski and Dunean, I975). I chose one

in which food, in this case sediment, labelled- with an isotope (laC) is

fecl to the ani:rials, and upta-he moni-Uored untj-l significant l.oss of t,he

isotope occurs through respiration or egestion. Rigter: (fgZ.f) antl ilarrey

(fqZf) used a sirnilar method for estimating the fil'bering rate of

zooplankton oeeding on a1gae. A1so, I measured the rate of faecal

pel1et production by the shrimp in the field in order to calculate

percentage assimilation of the ingestecl sediments and to checl< r'ate of

assinila'rion obtailed by suruning ,iata otr netabolic and pÏoductiotr tates.

Conoverrs (1966) method of esti-mating percentage assinilation from cifferencr,;s

in the percentage organic rna'uter of the food and faeces could not be used

. because it assumes the animal ingests without selection; this r,¡as not so

as shovm in the last chaPter.

Investigati.on of the feeding dynani-cs of briue shrimp (¡"-æ"fi",g)

has so far been eonfined to the laboratory (Reeve Ag63arbrcrd and I'lason,

f96¡). The shrimp l¡as considered a filter feeder of algae altl:ough

96"

llardley (fq:S) claimed a vild popu-lation in the Great Salt Lake, Utaht

ingested sedinents" Reeve de'bernined *',he effect of alga1 concentretion

on .bhe ingest:Lon and. fj-l-tration Ïâ+t es of the shrimp. He found, as have

nost others, a constant ingestion rate but decreaslng filtration r'ate above

a critical- concentration and vice versa belovn 'He also stud'ied' their

procluc-bj-on of faecal pe1-1-ets in culture. Both Reeve and l''iason r'¡ere

particularly interested. Ín the ef'ficiency vith i.¡hich foocl was conver''¿ed

to shrimp bj-omass and- the effects on thj-s of variations in tempera'bu:"e'

saliniùy ancl food. conceu'bration. Mason made some estimates of 'biris

efrficiency by feeding Uc 1abelled algae ancl measuring +'he amoruit

incorporatecl into the bj-omass of the shrirnp, but usually both authors

depend,ed. on ineasurements of +'he r,reigh" of algae consu-luecl ancl the Subsequerr'b

gain in r.reight of the shrinP"

Fer¡ estj-mates of the ingestiotr rates of aquatic invertebral'es have

been macLe direcil;,r in the field. Daborn (l-glS) in hic study of the

energetics of the J-arge predatory anostracan Bl-iÆg estinated feeding

rate by coun'cing the mrmber of prey eaten in bottl-es submerged for tilent¡'

four hours. Ano-bher study ernployi.ng fiel.d rneasulenents is llaneyts (rgr;)

e:carnination of the grazing of a zooplankton con-nunity' lle d'esigned

a feeding chanber that first samplecl the zocplankton ancl then released

knor.rn ano'nts of bacte'ia 1abe11ed lvith 3tr" By rneasuring body bu'den

of isotope af-r,er a short inc.ubation fi.ltering ra'bes of the commuli+"y

eould be calc.ul_abed. ancì thus the percentage of the suspension in tire

lake that r"¡as fi-ltered.

llo one has estinated rates of ingesti-on of deposit feedei's in

the wi1d. Holrever, Hargrave (fçZO) nad.e a tho'ough laboratory study

of the inges-bi.on rates and assirnilation efficj-encies of the arrçhipocr'

llvale1f.a-¡¿z-bec¡l feeding on seclinent. lle seeded sterilised' mud samples

r¡ith various radi-oactlve bacteria or algae (isol-ateci ori ginal1y from natura-l-

87"

sed"irne.t) and af'ter measuring their uptalce, shovecì. tLrat their assinila'tiort

ruas in general 5O/"" Ho\.¡etrer¡ he found that' the iotal organic mat'i:er in

natural sediment \,Ias assimilated with an effj.eiency of orlly 7'15/" (':sing

Conoverts method) and tha'b nou-living organic mat-ber such as ligniu or

cellul-ose r.¡as not digested at all. He conclude'd that only a sma'll

fraction of the total organic materÍal i-n the secliuent 1¡as available

for digestj.on. The sedintents of my lakes have a rruch lower organi-c

content than his (which v¡ere abouf 50% organic) and probably contair'

few a1.gae or pÌrotosynthesising organisms because of the high tu:bidity '

l4ethods

(") Iso e exl) ts

The iugest,ion rate of P-r-ziclz,i.ana lras neasured six tlmes i-ti

pink lake betr.¡een J-une and l,lovember 1975. On',ohe evening of the d'ay

before an ex'erirnent a mud sample vas taken (as described in the las'u

cha.pter) a'd rei.r:-rned" to the fielcl st,ation i-runediatel;" Any supe¡na'r'ant

r.¡as decanted ancl after thoroughly nixing the sample with a glass r"od

50-90 m1 of r,¡et rnud were placed in a one l-itre beaker' To 'chis

approxirna LeW 5r*ci of u [u-1acl glucose (zaL nci nù'f-l, P'adioc]reinical

Centre, Ärnersham, U.K.)vere added and r¡el-l mixed into the mud' Il-eisòher

(tglÐ and llooC and Chua (tglù showed that f i0-ghre'ose was rapitìly

taken u-p by rnicro-organis¡ls in sedir,rent. The rtud was incubated overnigh"

for eleven to ei.ghteen hours at room tenpera.ture (8-12oc). The ne/c clay,

at the 1ake, approrinately 1.OO-2OO rù of filtered (particles<ZO}¡t) :-ate

l¡ater collectec lmned.iately beforer wel.e introduced', anc the conten'bs of

the beaker stj-rrerf and left to settle (5 ninules)'

During this inte rval- P ' zi9Ø@ l¡ere sampied r'rith a 200

zoopla,nldon netn One hu¡rd.red and. fifty to tvo huldred. shrirnp uer.e

used in each experj-ment. These uere placed. in the beaker after removing

those clarnagecl. Their aci;ivity appeared ruraltered by the handling v¡hich

88.

toolc abou'b five minutes. À diverrs lead wc:ight (i.5 kg) taped to the

bottom of the bealcer enablecì it to silk; it çlas ¡:lacetl in shallo"¡ t"ater

2at the edge of 'bhe l-alce, inslde the Ool m" sampler (see chapter 3) to

prevent dj.sturbance. Lla.ter. temperature ïras Itecorded-.

The stalt of the e>qteriment r.ras considered. t<¡ be the moment the

shr.inrp were acìcl-ed. Just before thÍs three ?-5O lJ sanples lrere takent

tl¡o of the sediment and one of the supernatant. An au-tonlatic pipei:te

with removable tips was used-" The orifice of the tips used for sampling

the sediment haci been widenecl to pr.event clogging by removing the na1'Tol¿

encl. Of the tr.ro secLi¡nenb samples one r,ras pipei-,ted in'to a scintillation

vial containing l'O ml of a scintillation cocktail, I'Instagel-rr (Packard

Instrument Co.), that absorbs large auou¡ts of t.later; the other '¡as

placed in a glass vj-aI ancl sealed. The modified pipette tip probably

d.id. no.L clispense 25o/,L, but it sho'.ûd have dispensed equal amounts of

sedjment into the tr¿o vials. The supernaiant sarnple r"ras also pipeitecl

into 10 ml of trlnstageltr. By taking this set of three sarnp-l-es every

hou:" for ü-re three hours of the experilnent any changes in the specific

activity of the sedirnents or the supernatatrt could be determinecl' r\t

the end of most experirnents an aclclitional six pairs of secliment samples

vere taken to check r^¡hether the variability in the previous four could be

repeated.

For the first ho'¿r of the e:çerimen-b the shrirnp were sampled' er¡ery

fifteen ninutes and thereafter usually every half an hour, but sometj-mes

thisvaried.Oneachoccasionusuallymorethanfifteenshrimpwere'caught except tovards the end of an experinent r¡hen So¡neti¡nes nurnbers

ran f-ott. The shrinp vere sampled using the top one thi::d of a small

plasti-c bottle (dianeter 1. cm) r^¡hose screw cap had a hole with a d'isc

of zcroplankton nesn (ZO:S¡') insert'ed. This r'ras an efficlent' devi'ce for

the confined space of the beaker. shrinp r¡ere rj.nserL uith lal<e r^¡ater anc

sorted. into arbltrary size classes (same as those in Chapter /u) by conparir':g

89.

them r.¡ith the relevant lengths incised on a strip of plastic, then counted

and. pla.ced in scirrbillation vials containinE I-2 m1 of rrSoluenerl

(packard fnstrr:ment 0o.), a tissue digester, lifean inclividual length cf

shrirnp in each sample r,¡as subsequently calculated. and converted 'bo weight.

At the field station, the sedirnent saniples j-n ordinaÏy vj-als were

r,¡ashed r¡j-th fr-esh r.rater in the same lray es l,iere those for cal.oric measu-re-

ment (see chapter 6) and stored in desiccators for 14.Ì;er drying (at fO5o0)

and weighing. Sarlples in scintiilation vials were counted r¿ithirr about

two weeks on a refrigerai;e.d- Paclcard. Scintillation Coun'ber. Before 'r,he

shrirnp sarnples were courtted, the digests r.¡ere honlogenJ-sed using a glass

rod r¡igr a fla*utenecl tip until onJ.y a few speclts of exoslçeleton rernained"

The roct was t¡ashed r¿ith rrDini}ulerr (Packard Instrument Co.), a

scj-ntillation fluicl compatibl-e l¡ith trsoluener', md the contents of the

vials rnade up to 10 m1. In this way self absorp'Lion lfas avoided. All

vials r,re::e wel,l Shaken before be|ng counteO' l;o resuSpend any inater:ir'rl

'r,hat had se-btl-ed.. Rapid se'ttling t'ras only a problen r^úth sedinent

sanples, but these ruere suffici-ently heavily labelled to obtain a pr.'ecise

cor:nt (error =5iá) in one mi-nute; counting for shorter pc:riods did rrot

ali:er the c.p"rn. Generally all samples wer"e counted to *tt ut"o¡ -'5Íá"

Any cluenchi-ng was corrected using a calibration curve rela'bing exter::ral"

stand.ard- counts to cor¡tti-ng efficiency of internal stanclards. unqu'enched

samples ha¿ a counting efficiency of 9O%" I'fost of my sanples had

efficiencics betr,¡een 60 and, 9o1/ú rarely \"'as there an efficiency less than

5O/". Background cognts '"¡ere subtracted after measuri¡g the¡n r¿ith víals

containing 10 m1s of ej-ther ItDilni-lunefr or rrl-nstagelrt, foiltueirty four

hours before counting a set of samples'

(¡) Faecal pellet nrorl.ue tion

Provid.ed tire lakes wer:e not too rough, the output of faeca-l- pellets

l¡as measuïed. on each visit be+r,r,¡eer Novern'l¡er A97/+ ancl I'iovenber 1975 to

90"

eithella}ie.Asbefore,shrimp\Ieresampledr"litha20o¡zooplanktonnet

an¿ the catch poured. through a clisc of coarse mesh (about 1 run) to

separa+,e sma"l1 ostracod.s. The remaincler r,¡as sorted to renove any l-arge

ostraoocls and. any dead or cla:naged Shrimp. Then the O'1 n2 satnpler r'ras

anchored in the lake by pïessing it into the bottom nud as far as possible

and a 2oo¡.,zooplanl{Ì;on net fixed 'bo its sid.e in the frarne holder provided'/

(see chapter 3) so that the uouth of l-.he net ç¡as weLL above the I^Iate.rt

but gre bottom hal.f or more tras subme:'ged. The net lras careful-ly iot¡erec1

into positj.on so that r,¡a'ber ouly enterecl- through j"bs sides thus be'ing

filte'ecì. Abou-t tr¡o hunctred shrirnp r.rere placecL in the net (in r.*rich

they slrarn as actively as 1n the lake) arrd -l-eft forbt¡enty four hottrs"

Âny faeces produoerl fell inbo a coll.ecting jerr. At the end of each

ex¡lerirneni shrinp Ì{ere renoved and. any pellets clinging to the net

shaken into the jar. shrirnp and faeces Ì¡ere washed i'n fresh l¡ater

at the field station, the shrimp countecl and botli storecl in a desiccator

for later drying (the shrj.:ap at 6OoC, the faeces at 1O5oC) anc1 r'reigiring'

.any clebris falling to the bottom of the jar during the e"çerinent "¡as

removed cluring the washing of the faeces. such contarninants r¡e:'e few

and a}.rays obvious. ]f there vas 'significant rnortality, the ex¡leriment

was d-i-scard.ed.

Resu]-ts

(u) Iso exÞerl- ents

plots of the uptake of Mc against time are shou¡n i' irig' 2On

Tvlo regression lines can be calculated for most of the e>'perinents

representing two rates of uptake; a high initiat rate that lasted

approximately one hour foIlor'led by a slor'¡er or zero raten fn short

term feeclÍ-ng experiments such as these it has been siror¡n (tij-gl'er', \97I;

Haney, 19?1) that the point, at which-bhe initial ra't'e of uptalce cleclines'

mark.s the beginning of defaecation of labellecl rna+,erial by the ani-nal'

FTGURE 20

'tlThe uptake of aC by P. ziel'ziana. Regression J-i-nes

were calcu-lated. using all pointS except the open eircles.

In Graph 1 the high value for the first sample probably

resulted fron not rinsing the shrimp. In Graph 2 i.'}:e

points representing the 2 and Jh sanples have been

onitted; these are 109.6 attð' I\/v'I DPM individual-l

respectively. In Graph ! the 1ow points probably

resuJ.ted from dead. shrimp in the sarnples. The

horizontal line in this graph and the less steep line

in Graph 1 r^¡ere fitted by eye. Equations of the

regression lines are:

1 : DPM = 0.3 + 17.6lni DPM = U.8 + 5.Ih

2 : DPM = 2.5 * 30.2 hi DPM = 28.5 + 7./+h

3 : DPM = 3.4 + 27./+h; DPM = 30.8 + 11.9 h

4 : DPM = 0.8 + l/+.5 hi DPM = 15.0 + I.6 h

5 : DPM = -3.8 + ]58.6 h; DPM = ]-36.0

6.: DPM = I.7 + 2.6 h

I z5 .¡un. ?5

o

2 22 alul. 75

3 ts eug. 75

a

o

a

20

t40

70

a

ro

hours

4 14 sepÈ. ?5

5 lz oct. z5a

o

6 9 Nov. z5

a

a

40 oa

a50

a oaa

a

t-o=pEIC.;fLô

oo

o

70

a

a

2 2

\

92.

Therefor,e the high inj-tial ::ate of uptake ropresents the rate of

i.ngestion of sediment by the slirinç r+hi1e the lower subsec¡uen'l' rate

probably reprcsents tlie rate of assimi.l-ation. The equations of the

lines are given in the legend. to Fig- 20 and the conditj'ons under r'¡h1ch

each experiment r,¡a.s conductecl in Table 18. The points in Fig" 20

have noù l¡een correctecl for varia'tion j.n mean incìivldual d'ry vreight

cluring each e¡Peliment.

Before ca-],.cu1ating actrral r'ates of irrgestj'on of ¡¡s sedirient' j-t isr

essenti¿rl- tc shovr tha'b thei'e j-s; no cha'nge in the specific activi'r'y of the

sedinents or supernatalt during an e4leriment and there is no res;¡ri'r:aì;iol"r

of isotopc as 14c0, while the higher rate ofl uptake prevails" rt is

possible that E ii;.q_t4..ang iras a netal¡olic pool that tur:ns oveÏ incorning

energy rapic1l.y, as Lanq:erf (f975) shot+ec for L.-pÉSë"

The first is demonstlatecl j.n Fi-g. 21 by the laclc of significant

variation in the DpM of mud. and. suircrnatant sanples taken during each

experinient" The DPÌ'l in ihe nuil sarnples are the more variable' bub suclt

variatj-on only occurrecl because iÌ; was inpossible to sanrple a cons-bant

volu,ne of the secliments r^,ith the automatj-c pipett'e. This is confirinec

by the faet tLrat variation during an experfunent r'¡as usually repeated'

j-n the set of samples tal<en at the end'

The second c'f the above tvo assu¡lptions cannot be denonstratecl so

¿irectly as t¡e first, Hovever, j-f there was signiÍicarii; loss of U'''on

from the shrirnp throu.gh respiration while tho higher rate of uptalle

prevailecl then the regression line represeniing this shculd not pass

through.bheorigitr,butshouldintercepttheY-azjsatapositivevalue.

This uould indicate that there r^ras at the beginning of the e>çerimett'u

a shor,,: period' with an even highe:: rate of intake during which thele was

no loss of isotope. Table 19 gives the stanCard errors arrd signifi'cance

of the íntercept and regression coefficient for this iine' In rro case

TA3LE 18

Conditions dr:ring feeding experinents

e4perirnent nean d.ry weighta of anindivid'¿a1 sirrinP in a'

sample for sein'"iLlationcounting

o.z9 (jo.to)

r.r9 (h.zz)

o.66

0.?6 (19.14¡

232 (!s./r7¡

O.2o (tg.s7¡

total nr:nber of indiviCualssarnpled for sciniillationcounting

99

72

363

rg2

106

r59

ternperatur" (oC) salinitY (% )

1

2

3

lr

5

6

13

T3

13

rg (:-z-zr)b

i5'rg (rz-zr)b

1/+0

135

r20

89

105

9c

\oU)a

4 calculated from length to dry weight regression (Fig. 8, Chapter d)er-cep'r, for eryerirnent 3 vhere a large sanple of the shrimp to be

usedl r.¡as taken before tÌre staz't of the e>çeriment anC- dried and

weighed

range obsei'ved during the -? hcur e4perirnentb

FIGIIRE 21

Variation of the DPÌ4 in nud ( o ) and superna'tant ( o )

samples taken d.uring the feeding experiments. At the enrl

of experiments 3 Lo 6 a set of si-x or seven additional

rnurl samples wel:e taken"

4 14 sepÈ, 75

5 12 oct. 75

ó 9 wov. 75

I 25 Jun. 75

2 22 JttL. 75

I

ó

4

2

I

6

4

2

t_1oIttf\¡

(r)

ax

ùo

3 19 Àu9. 75

I6

4

2

22

hours

sta¡rtlard error of regressioncoeificient

!Æ!r ro.

probability ofcoefficientequalling zero

proportion ofvariation exPlainedby regressioir (r2¡

stanCani errorof in'r,ercept

o.ÄJ

/+.3O

3.LO

!.L2

9.70

0.80

signifieanee ofd.i-fference ofintercept fronzeTo

lìoSr

TI¡So

IÌ"Sr

Il.Sr

Standard. errors and. signifj-ca¡ee of regression coefficients and intereeptsfor regression lines rãpresenting the lnitial rate of uptake of DPI'{ in thefeeding e4crinents

experinent

1

¿

3

l+

É

6

0.60

E ln).41

3.!O

2.30

17.00

0.50

0.01> p> 0 "00L

0.01>p>0,0C1

p <.0.001

0"01>p>0.001

0.02>p>0.01

0.01>p>0.001

0.998

0.88/r

o.95C

o.g2g

0 "978

o.7gg

\o\J\a

96.

did the intercept cliffer signifi-cantly frorn zero thus making it unlikel-y

that there wes any short tern loss of l'/'C" ilaney (lqZf) r'¡as also u-nable

to detect this.

The slopes of the lines, i.e.'bhe rate of up-Ì:ake of DPilt were

highly significantly d-ifferent from zero a,nd the regression usually

acconnted. for at least 9o/" of the varia'biotr. und'oubtedly sorne of the

uree>ç1.ainecl variatj-on couJ-d' be accoun'bed for by error of the

scintj-l-lation e.ounter, but this is not shor,¡n otl the graphs (lilj' ZO)

because it is insignifieant compared. rcith the biol-ogical variation'

Table 2C gj-ves the errors of i;he leglessi<.rn coeffj-cien'Ús for the Ïeg1'essjLon

l.ines representing uptake after defaecation Ìras begun" In no case

where an error cou-l-d be estinla'bed v¡as cne coefficien'b si-gnif]catttl-y

d.i-ff erent froia zero.

Froln the clata on the dry lreiglrts of one member of each of the

paired.25o¡*Iseclimentsamplesthespeci.ficactivityofthesediment

c.u1d be estimated in ärg DPi"l-l. By mu1iiplying the ini+'ia'l rates of

1ì14c rrptake ruith these '.,he rate of ingestion of rnud is calcu'laterf a"';

shor,¡r -in Table 21. the 957, confidence limits of thi's rate are also giveri;

again the errors of a prod.uct are shot¡r to be doninatecl by the larger of

the tr.¡o constituent errors. The errol:s in specific activity are

probabl¡, l-ess than o.ìJo-t,ed' ín Table 21' l'7hen pairecì sediment sanples

were'r,aken the percentage error in those veighec approxlmated-that in

those measured for DPì.f, indicating thai the same variabil-ity in the

operation of the pipette prevailed for both sets of sarnples' This is

. obscured in calculations of the errors in specific activity because the

variationl¡ithinapairuasoftenasgreatasthataaongoneset.

Valuesforthed.ryr,leightofmudingested.areonlyaccur"atepro.'rirlec1

there is rio selection of specific particles e.g. organic" As shot'rn in

the last chapter -bhere is selection because the calo::ic value of tire faeces

is higher tharr t.'re rnean val-ue for the secliments. Therefore't'he values

ÎA3LE 20

stand.ard errors and. si.gnificance of regrel slon-coefficients for regression linesrepresentiag the iàt" õr uptake of DpM-irr the feed.ing erqperiments after defaecation

has begunç

experinent stand.ard. error ofregression coefficient

6.2

]-.5.6

3.2

t 1ir"t fitted by eYe

sígnificance ofdiiference of coefficientfrom zero

proportion ofvariation erçlainedby regression

a

a

1

2

2

4

5

6

llrSr

fl.S¡

TìcS¡

I¡'P'

no defaecation

o./r2o

o.366

o.o77

\o\ta

TABLE 21

Rates of sediment ingestion and their 95% confidence limits estirnated froninitial rates of uptake of DpM ana speåific activities of the rnucl. T.ne 95/'

ãonfidenee limits ^r,¡ere calculated u"ing the equation in chapter /+ lores-r,imating the variance of a product'

erqgeriment initial rate of-upiake (Oeu 4r;lindividual --L )(.)

95/, canfidenceI].mafs olsoecificu"ti"it:' (%)

95/, confí-d.encelinits ofingestion rate("/,)

J-

- 4¿.O

95/" confidence limits speclfic activityái" uptatce rahe (%) of sedir'rent (Bs

d.ry :,rt" x 10-¿DPì,rr) (U)

1

2

3

l-

q

6

!7 "6O.5/+ a.95

30.2 a.75 2.26

1l c4 0.52 l./*3

I/r.5 r.63 2.36

t59.6 0.82 13.01

2.6 1 2.2 o.35

c no esti¡nate becau*se paired sanpl-es (25Cf1) of nud (one for weighing; one for measuri-ng

DPM) not taken

d "annot

calcul-ate, but probably about' 5OiL

Ih

50

tj

U

3

a

-L: 3r.8

+j 51.0

-L: L6.r

I! 45.o

c

Á

d

I)- 116.9

J-! 2!.5

I! 58.2 J 5ô. 1 \oæa

j

1

t

39

T6

22

0

o

2

t

99.

j-n Tabie 21 are probably over-estimates and are bet'ber consiclered as

r,reights of rmrd searchecì., but not tctally ingested by the shrimp.

Accepting that some selection of secLinent particles exists

'bhe lnaximurn c1ry weight of naterial in one ftú1 gut can be calculated by

assrming that this is lepresentecl by the DPl4 j-ngested up to the point

t¡hen -bhe ini'Lial uptalte rate decl:i-ties. For bhe Sep'r,ember e>periment

(graph a, Fig. 20) this rceight equals 0.28 mg r¡hich compares favourabl.y

uith t¡e volume or weight of 0./i{-0.78 rng calculated from measurements

of the length and r.,-idth of the averege sized shrimp (arbí'brary size

cl-ass 6 to ?) used in this e>qreriment. Values cal-cul-ateil lihe thj-s -v¡iIl

of coulse be larger than val-ues frorn the isotope experiments because 't"he

latt,er oo not include the volume or r+eight of fluicls. Despite thist

because they are of the same order of nagnítude, 1t is reasonable to

assume that the poi-nt r¡hen the rârue of the isotope uptake changes does

indeed mark the s-bart of defaecati-on and thus that the esii.mated rates

of sed.j-rnent ingestion are uithln the posslble range. 0n1;r a rough

cort"espondence can be e>çected- r,¡hen both calculations are subject to

l-arge errors û

(b) Faeçal pelIet Tlrodlctioq

The results of the experi:nents measuring faecal output are given

in Tab|e 22. On three occasions in Pink Lake (December I9^/L, IaLe

Jwe 1975, i{ovember 1975) most or al-1 of the shrimp dj-ed ove¡'nigirt in

the net and so the aeeurnulated pellets were no'b collectecL" Possibl¡'

the shrir,rp in these cases l¡ere starved by being separated too long frcnt

se.d.iment. Hovever, shrimp must have been able to replace their gut

contents ruith suspended sedinent particles d.uring *,hese e4leriments

because ',,hey produced. a. greater weight of pellets in tt¡enty foul hours

than could ì:e provi.Jed by the weight of material in a fu11 gut" Usually

their guts appeared as f\rll at 'the end of an experiment as at the starL"

TABLE 22

Faecal pellet prod.uc-tion of P" z-leþz'ilLana r.¡hiIe swiroming in the water co}:¡n

Month Iake faeeal ouputng 5 1O-2 Cry wt¡r-r individual-

)1)..j-

2.3

7-A.5

20 "3

1.1b

'3.5

0.8

5.3

2.5

number of shrimPused

rnear. dry weight. of an individ"¡aI1 ('e)

temperatr.rre range (oC) salinity (/"")

N.c,¡. 1974.

Nov. 1974

Dec. L97l+

Jan. 1975

June 19?5

Jt;Iy L975

Aug. l-975

Sep. ]-975

OeL. 1975

Cr-r¡dare

Pink

Pink

Cundare

Pink

rAT,K

Pixk

Pink

Pink

0.66

o.32

0.86

¿.o¿

0./+7

1"604

0.18

0.60

0 "35

/+36

IILT

280

9lr

t23

99

ioo

52/+

199

1 ?-] o

14-1"1

]-5-2r

l5-23

1"0

10-12

11-12

18-19

T3-T5

E,L

oÃ

lO2

öy

L38

t35

720

89

ra5Pooa

a weigh-b too high because shi'imp not i¡ashed ihoroTghl;- infresh r,i9Àuêr.

b shrimp appearecl bo be nainly lngesting algae'

101.

Such tur.no\rer carn be denonstrated. for the j-ndivj-duals used in the isol"ope

erçerimen.bs (table 23). On average, the weigirt of pel)-e+"s each r+ould, have

procluced. r,¡as 'ben times -bheir gut veigh'b (calculatecl ¿rs above)" Tbese

conclusions assume littIe contribution to faecal pel1et prorluctioil by

phytoplankton ingestion; l¡hen P. ziet'ziana seemed. to be feeding largely

on algae (Jr-rne, I975i Table 2Z) tne r,reight of pellets produced uas very

low for the size of animal used.

Discuss:i-on

The accuracy of the rates of energy in'ualce calculated- flom the

feeding experiraen'r,s depends on uniform incorporat,ion or l4cl*glucose into

rnicro-organis¡ils; these constitute a third, of the calories (chapter 6)

i-n the sediment. During the overnigh'b incubations 7O-8AÍ" of the iso'boPe

v¡as lost (tatte 2.4). 0n1¡r {'¡u productio" of I4c0, from bacterial

netabolism of the glucose could accou¡t for this. llith such turnover

it is 1ike1y grat the renaining 2O^30',f" had been unifonnly d-is'bribut,ed.

Others (Sorokin, 1972; llood ancl Chua, )-973; Eleischerr 19?5) r"ho

have followecl the uptahe of l4c-gtucose by rnic::obial populations in

sedinent have also found ::apid turnover ratesn Elei"sher clenonstr'a'Led

wi-,,h chromatography that v¡ithin 'Lhirty ninutes of labelhng mos't of the

glucose had cii-sappeared and labelled compounds of high mol.ecular weight,

probably polysaccharic.es, r,y'eÏ'e being procLuced. Ti' j-s tuosl' -ur¡1ike1y 'uhat

the observecl l-oss of isotope lras caused by non-biological deccrtposition

of the glucose. Accorcìing to the nanufacturers such deco;nposition

occrÉs at a rate of about Uil a year at -2OoC'

I,ll-eischerr s d.emonstration that high mcleeular weighi organics

quickly becarne 1abel1e,1 j-s supported. by 'che vork of l'licholas and

Visr¿anathan (L97Ð on ihe feeding ot l'4c l-abelled !-scLe4ÈgÈ to

the nematod e ce_ÊngaL+ÞO jj]1q--þËigÂ8g. They fcr.rnd a nmch higher proportion

of 1/*c lras incorpo::ated ini,o the bionass C. b$-rJ¡sae trhcn E" coli were

102.

TABTE 23

The estimated weight of a fu1l gut for'an individualused in the isotope erçeriments compared l¡lth theweight of faecal pellets it r¡ould have produced intr,renty four hours isolated' in the water colu¡n.Faecal output is calculated' from the regressionequati-on in Fig" 22 re1:ati.ng it to ruean lndivíd'ualueight.

erçeriment weight (me) of a fuJ.Igut

wei-ght (mg) offaecal pelle'bs producedin twenty for.¡r hours

1

2

3

lr

5

6

0.11

0.28

0.27

0.28

1.07

rro defaecation

2.U

4"IO

1_,62

2.O3

TT.66

TABTE 2¿

ernatantfractionsdurj.nganisotopeexperimentad-ded. Values are only approxinate becauseread aceurately from the narkings on a one

supernatant rnay have increased near the

sediment surface

erperinent nud(nru x ro

A supernataPt") (oÞtu x roo)total(DPM x l-06

incorporationv")

ti-ne of e>çosure ofsed.iment to 1abe1(tr"s)

a7 "5

16.8

L7.0b

].6.5

L3.O

ro.5

)

1

?

3

lr

5

6

!.57 1.0/+

1.83 o.4oa

r.32 L.25

0,8/o 0.82

2.57 o.77

2.25 1.0/,

2.6L

2"23

2.57

r.66

3,3/,

2ro

Ho\¡¡a

¿t

20

¿t

t5

3o

)c

a.r¡nrd not well stirred before start of erçerirnent

b only approximate because starti-ng tirne not recorded'

104.

pre-labellect r,¡ith 14c-gln"ose ra'bher than r¡ith ttaH14CO, t 37/' awl'

Il-24, respec*rive1¡'. This, they suggestecl, r¡as clue to g1-ucose being

clirectl-y incorporated into structr-rral eornpounds ín the ìrac.Leriat o'$o

polysaccharicles, anrf subsequently being assinilatecl by the nematode

r.¡j-thout being brohen d.own to labile metabolites" Tl"ts 1/*C left in the

sediment after ¡neta'bol-ism of 'bhe glucose tras prrcba'bl;' 1n"u*orated as

s-t,ructuia1 conpouncls in the bacteria'

Theie is other organic lia'bter in the secU-meu'i; possibly non-li'riIg.

Calcu-]-atlons of ra-bes of energy j-ntake assume that all the olgatric matte::

is in3ested l¡i'bhout selec-bion. The abilit)' of P. zj'9.tZig,t4. to produce

faeces of si:iúlar calorj-c value to the sediment l¡ìiile fí'1t,er:ing in the

l¡ater column confirms tlús by indica'uing that -bhey ingest rnaterjal of ¡iorr:

or less the same orgauic conpositiou r^¡herever: they feed. sma11

d,iscrepancies are probably not cìetectable consid'ering the r'¡icl't'h of the

confidence linits of the ingestion rate (tat1e Zt). Selectiorr of organ-ic

palticles of sedinent, (e.s cpposeä to selec'cj-on of par¡icu1ar orga'nìc'

matter from the range available in the secliment) car'not affect

calculations of the rates of energy intake, although it Ìdl-I cause

over-estima'bion of the lreight of sediment ingested'

Tr¡o further possí-bilities exist which ca'n j-nvalidate the feeding

e>,periments" First labe11ed. bacteria could have adherecl to the

ey.oskeleton of the shrimp" This has no¡! been shovrn to occçr by others

(Rig1er, 1;971'; Haney, )-g7I) perforrning siririlar e4pe::imerits atrd has

thus 'been lgnored.; the sirrinp were rinsecL before being pJ'aced i-n

. scintil.lation via1s. The second possibility is self absorption r+hen

measuring the DPt,i of ',,he sedinent samples. This r¿as most lilcely

negligible compared. r.¡ith the variation in counts bett¡een sarcples'

Rates of ingestion given in Tar;le 2I i.n terms of ng d'ry lreigìrt

can be converted to calories (Tn'b1e 25) using t¡e values for caloric

coil-ue,'t of the sed.inetlts from cliapter 6. Â1so vj-'uh values from chap'ber 6

TA3T,E 25

The rates of enerry i¡take fot P. zieLziana ingesting sedimeni

experiment

4

0.95

2.26

I'43

¿.)o

T3.OT

o.)5

(t o.so)

(t r.ir)I(l z"so)J.(: o.r5)

334.6

27l-.9

!7/+.7

266.4

237.5

lg2.g

rate of ingestion ofn:ud., (mg d,ry wb. xtc-]'rri-l in¿:-vidual-1)!9 5/" confidence limits

caloric conient of-tsedimen-bsa (cal g *dry mud)

:'aie of ençrgy inteke(caI x 1o-a hr-1 indiuidual)!95/" confidence limits

I2

/+

5

6

o.32

o.62

o.25

o.63

? rìo

0 "07

-L(: o.:-4)-!(l o.3o)l-(: o.óz)-r(l o.o3) Ho

\l¡a

vaiu_es for first -uhree ermer.irnents are frcm rr'.:.c sançr'l e5 collecied near those

slbseo¡iently used in the ã;¡perinents; values for' last three e>perinents are

froin tïe z5o/.-*1- sarlples taken for veighilq agling an eryerimeni'" - All valuesaccorm-r, for 1e¿rchúg (see chapter 6, tabl-e 16) r'¡hich Lres assumecl to equal

thai r"¡hich occiirred r,¡hen washing t'he 25C¡'7 sedi¡aent sarnnles

106,

¡re rates of faecal ou-tpub (faUte ZZ) cen be conver'-bed to calories ancL

plotted a.gains't, nean incl'l'yictr:a1 r.reight, Fi-gn 22. Tt is not'r possible

to estl¡nate in tr+o vays tlie percentage of energy assj-ni1abecl i-n each

isotope erperiment" First the ratj.o of 1;he lates of uptake of DPI'I

befole and. after clefaeca-bion can be calculated.. Seconcl the rate of

ener-g'y loss th::ortgh faecal productÍon -for shrimp of a specilic nean

inrtividual 1reight can be interpolatecl from Fig. 2-2 and' subtracl,ed front

the feeding rate to p::oCuce the rate of assimilati.on. The results of

these tr'ro proceclures are shor'rn in Table 26.

There is soiue correspond.ence betr'¡een -bhe tt'¡o sets of vålues"

However, those d.erived. from the isotope e:çerimenrr,s âTe less a.ccura'be aird

nore inprecise because of tire large stanC-ard errors of the regression

coefficients and the probability that once tÌle rate of upiake of DPI'I

changes the shrimp are not only defaecating but also respiring'O'O..

(Lampert, I9l5). As shor¡n alreacl¡, the slopes of the regressio,, fil"'

represe¡iing the lol¡er rates of uptahe are no-[, significani;ly diffcreni

from zero. Therefore figures for percentage assi¡nj-la'bion from 'l;he iso1;ope

e>periments are not reliabl.e. To have a 1or¡ and- variable rate of

assinjJation of the major source of food. i-s, of courser one llay in r'.'hich

an aninal can starve.

valu,es foT percentage assillrilation basecl on rates of faecal

pe1let production are generally higher or equal to those from l,he isotope

experjnents. This is to be e;qgected for three reasonsc First duri.ng tlie

defaecation e4geriments the shrin-rp must fil'cer a solution I'rith a lor"er

conce'tration of sediment partieles than they would. enco-,r.n'ber if feecling

on the surface of the se<j-rrnent" As shor¡n they can still replace their

gut contents under these conclitions, but the arnount of inconing seC-irnent

is probably less 'uhan dru'ing an isotope e:çerjnent and' therefore

assi¡:ilation efficiencies quoied i¡ Tabl-e 6 are overestirnated. Seconci,

107.

iABtE 26

P er c enta g e as s i rnilation o f B-e---ä¡S+,¡ iq4g.ingesting sedinrent

e:çerÍment fron isotc'pe elq)eriments from rates of faecalpellet productj-on

26

27

28

6/+

58

6L

29

25

lrj

t-1

0

no defaecation

I

2

3

l+

5

6

r08.

it is possibl-e during these ex¡rerinents that the shrimp reingest cleposj-ted'

faecal pelle.ts, thus i¡creasing their pereentage assimilation. Thi-rc1,

faecal pellets rnay have been leachecl to some extent r.¡hile accu¡nulatj-ng

over the tr,ren1;y four hour:s. This t¡ould- j¡crease StiJ-l further the

assi.mi.lation efficiencies.

Thus values oalcu-lated. front rates of pellet produc'"ion are

probably ¡narimum efficiencies. lTeverthelessr nearly a13- tlie variatj-on

in üreir r.ate of prod.uction can ì-.e e:çlaineil by I'egfessing the 1og of

this value a.gainst the 1og nean indlvidual r'reip;ht (fig. ZZ). This

inclicabes ilrat the concen'bration of sediment par:ti-cJ-es in the wa1er cÚluarl

and fluctuations in tereperature and salinity (faUte 22) haci littl-e olr no

effect. Perhaps parbicle concentra.tion r'ras a1r'rays greatelbhan tire

critical level, as discussecl by Reeve (L963 a) for AJi sa,l':ì'nqr above

which ingestion rat,es retnai-n constant. This r;ou1c1 irnply that parti-c1e

conceir.r,ration neve¡ linited. the inges-bion rate of l* -zigt-zi-q-n-q t'rhen

feeding on the sediment sil-r-face.

The slope of 'r,he regressi.on line in Fi"g" 22 is \"5',7. Ït seems

to apply al-so to the fer.¡ rlata fro¡l Lake Cr,rndan'e and j-s noi s:Lgni.ficently

clifferent from that of the regression of 1og feecling rate against log

nea¡ indiviclual r.reight, Fig. 23" There is iaore unexplainecì' varia-bion,

however, in the values for feed.ing rate. It is unlikely that this j's

due to iemperature or sal-inj-ty f1.uc-buations 'oecanse these have no

influence on faecal output" IngeS'bi.on ancl de-Îaecation nust be vil-'cualIy

conti.nuous in P" zie 't ziena as specimens uith enpty guts are rarely caught"

Feeding rates and thus egestion rates pro'babl-y vary Ii'iitle diurnally

because respiration does not.

From ny obselvations ind.ivicìual shrinqo do not feerl con'cinuously

on the bottom, but periodically ascencl. Bi' do:lng so the;' subjec'b

themselves alternatively 'bo high ancl low rates of ingesbion and- thus high

and. 1or,¡ bacln¡ard direc'i;ecL pressuï'es r.¡hich mr-r-st reg"ulate tire length of tine

FÏGUNN 22

Faecal output in calories versus dry weight of an individua-l-

for P. zj.el.ziana. fron Pink Lake ( o ) and. Lake Cundare ( o ).

A value of 265.8 "rt g-1 dry faeces (Ctrapter 6) was used to

convert the rate of pelJ-et production from ng h-1

índividuat-l (fruf e 22). Two values recorded in Pink I¿ke

have been omitted (see footnotes to Table 22). The

regression line is: 1og (faecal output) =

O.5/+ + 1.5? 1og (mg) (r2= O.))/',i S.E. of slope = 0.068).

t-o=p!.Cî (_ao

_cô¡

'gX

oU

6.O

r.o

o.2

o

o

o.2 r,o 20

o

møcn dry wøight mg

FIGURI 23

The feeding rate of L--¿þ!M, i-n calorj-es versus the mean

dry weight of an indi-vidual. The points have not been

corrected for variations 1n tenperature and salini-ty (Tat1e 18).

The regressicn line is: 1og (feeding rate) -

â.20 * I.4g 1og (mg) ("2 = o.gz/+i SoE. of slope = o.2I4).

The bars represent iù]ne 95% confidence linits.

s.ô

r.c

o.l

a

L-o=9.z!.clL-1o-C

bX

E(J

a

3.Or.oo.2

mØcn dry wøight mg

].L1.

food renains i.n the gut. ,ILe longer it remainsr-bhe filorer pres'.mab1y,

can be cligestecl, Tiris r¿as sugges'Lcc1 Ly Reeve (lg6l d) to e>çlain the

hig'her grotÑh efficiency of 4r--r# a'L lot¡ foocl concentrations' At

such concentrations back pre,ssuïe was least" IIe also forurd' thal; 'A-. saU-na

enclosed each faecal- pellet in a ch.itonou.s nienbrane and proposecl that food

Uas plrocesseci on1.y as fast aS this nenttrrane r¡as formctl'" Occasionally

a nembranous sheath, open at ìroth ends, encl.osecL faecal- pellets produced

bv P. zieïr,i[Lna, 'tlut generall-y they lrere absent'

Therefore assii:rilabÍ-on percentages based on ra'bes of faecal

pellet prod.uction in the r.rater column nay not be as ove::-es-bj-mated as

inpliecl beforeo They are comparable r¿ith 1:ub1J.shed. valuesi for other

cleposit feeders" Hargrave (fçZO) sÌror¡ecl that the benthic arnp¡1poc1

H"a eca assilitilatecl ottly 7Å-5% of Lh'e organic f'a.ci;i-on r¿hich conposed

5O,q, of the sedirnent. Otr -the other hand', Davies (1975) formd tha'i:

chironoriicL la:'v¿re inges'ting sedlrtent r¡j-th a. 3-/+it orËanic con-Lent

a.ssimilatecì abou--r, 6511,. T\+o rnp-rine gast:.-opocls stuC.iecl by Nel¡ell (fç65)

l¡ould only digest bacteria in 'bhe organic fraction of their: faeces'

IfL*.glzlgqonlydigesteclbac+'erj.athentlreirna;<j.rnu¡n

assiniilati on percentage r,¡ould be Zi¡q", the fraction bacteria compose of the

total organics presen-b (chapter 6). Assimiiaticn chu'j'ng the first

three experi.en'bs (f¿tte Zó), calculated by either ne-thocì., i-s close to

th-is; cluring the 1ast three (considering only data based on pollet

prod-uc'rion) it has doubtecl. This suggests, j-f indeecl only bacteria are

digested, tha'r, the egestion r¿.tes for the last experinents are

u¡derestinated.Thereissomeeviclencefortlris:theirratesofener'ry

intahe lie above the regression line (Fig " 23) l¡irile those of the first

group lie below. Such coulcl occur if the seconcl group spent more tj'rue

feecling on the sediment surface, indicating -ihat its assimilatjon

efficlency shou.lcl not be based on egestion rates in the water colurìn'

LL2.

On the other hand there j-s also evi<i.ence that aIL the organic

natter in the sedinent is potentially useful to L--{ælZie4g' IYom

the cal-oric values for the secliment (chapter 6) C:I{ ratios can be

calculated by assr.;ning that all the o, used in the r¡et oxid'ation is

converted to CO,. Thi-s gives a ratio of appro:cimately 13:f.

provasoli and DrAgostino (fg6g) shor¡ed that À--Þgling.STew best in

cultures r.¡ith c:N ratios beil¡een 1?:1 and 11:1. The¡r a15o shor¿ed that

it r¡as an obligate phagobroph or particle ingester; nutrj'en'b soiutions

r.lere incapabl-e of sustaini-ng gror,rbh even at concentrations approaching

inhibitory 1evels" Vitamins, howeverr t{ere ingested as solubles' The

continuotrs g::owt}r of j¡rdivid.uals in each gerieration of

(chapter /¡) suggests that food cluality r¡as not limiting'

P. zi

113.

CI{APTIJR B - Enerry budgets fot',P-"-Zig\zia.na ancl conclusions

I4tlocluction íLgd Metho4g

once the prececling data have been converted to energy r]nits,

energy budgets for the varj-ous cohorts in Pinlc Lake and Lake Cu¡dare can

be presen'r,ed. Uirfortunately the bucJge'i;s cannot be complebed' for all

generaticns of P. gietz,!aJ.r.a. because there are only l:imitecl data on

ingestion rates. Iìowever, rateS of assimllation can be calcul-ated

for each cohort and. therefore in 'bhose for r.rhich tìlere are esti-mates oî

ingestion rate and. assimllatj-on efficiency T can oetermlne t¡hether energy

input meets energ'Y demand.

To convert procluction esti-mates from ng to calories eleven Cried

samples (app::oxlmately 2OO mg each) of washed P. z*ttz'iana t¡ere burnt in

a Galenkamp bomb calorimeter" Ash content of the shri¡p \ras deternined

separately af'ber ignition for tç¡o hours at 5OOOC; this gave an average

J+value of 33.0(f1, >)iL ëgS,t" confidence limits). The nean cal-oric

value uas 5.7 110.e) ""1. ,rg-l ash free dry weight (!gS/, conficlence

limits), ghicir:ì.s very close to the nost probable value cf 5.ó cal.ng-l

ash free dry r,reight quoted by !ü-nberg (19?1) for aquatic organisms"

However, it is possible tha'o the calorj-c value has been sl-ightly

underestima'¡ed becaUse 'r,he Sanrples fiere kept Í'-rr One "O

ti'iO yeai's insteacl

of a rnaximum of thirty days (recommend'ed' by Paine' 797r) before being

burnt. In this time some of 'r,he organic material may have been

partially oxidised.

The energy equivalents of oxygen consu-r'rption have been reviei'¡ed

-1by Blliott and Davison (lglS). They concludecl o Qo* of 3.38 cal mg *

j-s suitable ior herbivorous ani¡nals r'¡j-th a high proportion of

carbohydrate in their cliet, if RQ values are unavailable. The organic

LL4"

fractlon of the sedlnenis irÌÉt P!i-1-q!-A@ ingest contains 27 '31'

protejx end. thus 72.7/" carbohydrate and. fat. J\ssuning they are

¡netabolised i-n these proportions, I have used the Qo* aboven

Protein Ís not compl.etely ovidlsed. dur.ing catabolism and'

nitrogenous r¿asl,es are produced. By lanowing theír compositlont a

factor for enerry loss (Q"*) can be calculated fron the rate of orrygen

consr:mption" Parry (rgoo) clai¡ned. that crustacea wel.e anmonlo'veles

anct Bertrice (fgZZ) shor^¡ed i¿;,.,e1. 75/" of the tot¿r1 nitrogen excreteeì' by tne

anostracan r¡as arnnonia' The Q"* calculatod

bpr Elliott and Davj-son (tglt) for auunonioteles was 0'62 cal tg-1'

This r¡as used in calculating enerry loss for P.'- z'ietzialgt assumjxg t'hat

27,3/" of the food' they netabolise ís pr;feinn

Rpeultq

Tables 27 and, 28 gLve the amorurts of ellergy assiuuilated by each

cohort in Pink l¿ke ancl Lake cundare and thc rel-ative contributions of

production and ¡netabolisn 1n joules (4"18 x calories). In all eases

resplration accounts for ¡nost of the enerry assirnilated' Productj-on

contributes between 15 and 3Af" excep'b when the final stage-c only of a

generation lüere sanpled e.g. cohorts I and. 2 in ûr¡rdare and cohort l'

inPj-nk.The]-c.l¡percent,agesinthesecasesaretobcer.pectedbecarrse

nost of a cohortts production occurs through the death of the younger

anlmals. High respiraiion rates due to high temperatures and saJ'inity

or nortality through saLÍ¡ity stress¡ er$o cohort 2 1n Pink, also írtcrease

ùlris inbalance" Excretion of metabolic r¿astes is always less þinalll 5%

of the total and eonsid.ering that there is an error af /*Q fo 5A/" in the

production and resplration estÍmates this percentage is not significant'

ff the shrinp ¡netabolised only protein then it r¡ould increase t'o IÚ""

In Tabl-e 2,) rates of assfnúlation cierj.ved fron the feeding expelinents

are compared wj.th rates of respiration predi'cted' for shrinp of the se'me

welghtasusedintheseexperlments.Ineacbcaseexcept4

TABLE 27

The amount of energy assi-mi-fated by'the various echorts in Pinl< T,ake. Al-1values are in jou-J-es 0.1 m-Z (Z*.tg x caiories). Excretion represents energyloss through ni-trogenous r¡astes assr::ning 27.3% of the assiniiabte foodis protein. Figures in brackets are percentages of the totai assi¡nilation

eohortsa p::oducti:on (P) respiration (n) excretion (E) assi¡nilation (1,e, total)(A)

I2

/-

5

6

7

65/19.6

11.9

18239.0

23673.tn

2/+66.2

2566"r

¿)).ó

( z.a¡

( z.s)

(zz.s)

(tl.z)

(ts.s)

(11.9)

(32.t¡

7360/t.8

392.9

58745.7

108805.8

i2800.4

/+7 5/*.3

, Èa -4la.r

(Bz"B)

0z"t¡(t3 "5)

( ze.9)

(so "5)

(62.9)

(6tr"l)

3685.9

Lg.6

29/oI.9

5/t".8 "6

6/10.g

239.3

23.8

(lr.t)

Qr.A¡

(l "l)G.9)

(zn. o )

(3.2¡

(3 "2,\

g3g/+O.3

/t24.4

79926.6

I37g2'-i.g

r59O7./+

7558.7

735 "7

326320.9

Toial =

¿o

e

L m-2-1yr*

o

302i.

o;/¿o2C))

a PH\'ro

7,637169/*.5 j¡n-2 y¡-I

lota1 53742.0 (16.5) 25?5SO.A (79.5) rzggí"g (z*.0)

a as described in Chapter d

cohortsa production (p) respiration (R) excï'etion (E) assinilation (i.e' total) (A)

354.9 ( 2.9) rr/*s3.7 (92.5) 575.2 (4.e) t2Æ3.8

59.8 ( 5./) 1C06"1 (90.r) 50.6 (4.5¡ r]=16.5

TABLE 23

/+j5.2 (32.5) 859.0 (63.3) L3.r (3.2)

L?39.3 (tl .t*) 78/*5.1, (75.6) 392.9 (z-.0)

/,,g5.7 (18.3) zro2.r (zz.s) ro5.3 0.g)

Total 3LOtn.g (11"3) Z3Z96.3 (gZu.5) ]-167.r (4.2)

a as described j-n Chapter /,,

The amoqnt of energr assimilated. by the various cohorts i:r Lake Cundare.All values are in jôules 0.1 m-2. To calcl¡J-ate ener,.gr losses by excre'uion27.3/" of the assirniiable food. vas asÍluned to be prof,e:.n, the sa¡ne as in Pink,although the caloric value of nrud is lor'¡er in Cundare'

1

,)

?

/+

É,

1357 "3

9977.6

2ia3.r

27568.3

Total = 27568.3-j0.1 m-2 rJ yr-Li"e" 2L2r063.8 j6-2 yr-L

PHo.I

experiment

TAB],8 2A

Rates of energy assinilation by g ingesting sed.inent compared r^rith,itsrates of energy consumption through respira{ion. Assimilation r"¡as calculated fromthe percentagéL baseC òn rates of faecaj- pel1et outpu' in Table 26. Respirationwas iredicteã fron the regressi-on equation in Chapter J using_the valu-es oftenpãratu-r:e, sal-inity and mean indivicirral r.reight given in Table 18 for each feeainge><pãrimcnt.' Tìre uni'us are j x 1O-1 hr-f individuai-f .

. enerÂty intake (C) energ)'assinilat"¿ (4)

ëgsF äria"tt"e linits) (95f" õõntldence linits)enerry respired (R)

1

3

+

E)

6

I.3/+

2.59

1.05 (t o.¡g)

2.63 (! Uzo)

!2.g2 (t z.sr)

o.2g (1 o.r¡)

o.35

0.70

o.2g (0.t3 - 0./+6)

1.68 (0.88 - 2.L9)

7./+g (5.s6 - 9.L2)

0.18 (0.10 - 0.26)

o,59

o.7g

o./+v.

0.61

r.25

o.22

95% confidence lirnitsof predicted respi-rati-on

0 .5/* - 0.6/+

o.72 - O.87

0.43 - 0.5L

o.55 - 0.67

I.I2 - I"/+O

o.rg - o.25

HH-la

1L8.

and. 5 energy Ìras consunìecl at a higher rate b¡' respirati.on than it was

supplied. by assinÉla*uion. fn fact, bhe shortage is larger than shor"n

because the a.nimals were al-so grolring to some ex-bent as r'¡e1l as excreting.

In all cases, hovever, the rate of energy ingestion by P. zie'l,ziana ì/as

greater than its rate of consurnption. Therefore assimllation efficiency

nust Ìargely cleberrnine ruhether there r¡ill- be a shortage. fn these

calcula-bions ¿rssinila'cion is at a ¡naximum, as previously d.iscussed, because

it is basecl on egesì;ion ra-bes meas"rred in i;he r.¡ater cohunn ra-bher tharr on

the sed.ilnent srrface. Thus only by increasing ingestion rate can -shrin4r

survive in these conditions, but -bhis is onJ.¡, advantageous provided it is

not offset by a decline in a.ssimila'r,j-on effici-ency (see chapter 7). It

is, of cou-rse, possible that P._a-ig_Lzj,a¡a may be able to survive for soue

time on bocly reserves. Hor,rever, its caloric value (5.7 cai. rng-l)

suggests that large deposits of fat (9.J cai- mg-1), the usual form of such

reserr,¡es, are not present. Al-so at no stage do aninals that sur.¡ive,'l-ose

weigirt.

Consldering the r¡ide confidence Ìimits of the values for energ;r

intake it is turt¡ise '.,o rely '¿oo heavily on the accuracy of 'r,ireir

corresponding values for assinilation. Nevertheless, they suggest that

P. z'ie tzíana is unable to meet its energy demancl uhen feedirig on sedinent

r,lith a 1or¡ organic content because of poor assimilation. This j-s a plarisj.bl-e

e4planation for the consistent mortality in each cohort.

It becomes more conrrincing if the relation betr¡een the feedjng and

respiration -rates is follor.¡ed. throughout ''"he life of an individual. This

ean be done by comparing their rates of increase r,¡ith vreight, Fíg, 4. The

slopes of the two lj-nes (I./+9, O.76) are significantly cliffelerrt (p-0.00]).

Therefore sma1l shrirnp (=0.2 mg) wift not be able to ingest, 1et alone

assimilate, enough energ'y by feeding on serlinent to rneet their resoj-ratory

need-s and cohorts r.¡ill suffer a high Ínitial rate of nortaliiy. This is

evident for generations /ç and 5 in Pink and Cunclare (¡'igs. 6 and 7), provicìed

F]GUR^E 2i+

A conpari-son of the i-ncrease with weight of the rates of

ingestionand.respi.ration(uotrrinjou-1es)tor@..

The line representing respiration was calcula-t,ed for the

average values of tenperature (r¡oc) and salinity (tZ3/"")

in Pink Lake during the study; it uill move up or dowr

(but maintain the same slope) according to the values of

these ì;wo paraneters thu-s j-ncreasing or decreasing the

weight at r¿hich the tr¿o rates balance,

I

I

I

t-oaE't€.ç

îr_2o-c.

?gx

to.o

r.o

ingøstion

røspirotion

o.2 r.o

møon dry weight mg

s.o

1.20.

numbers recïuilred. aïe also cot-r,si"dered. (Îable 6). Periods of stability

or with lot.¡ rates of rnortalit;v fo11ow; these also occur in other

generatÍons, but, r,rith no d,ata on recruibment or Ì:ecause of rapíd death

due to salinity stress, high initial nortal-iby cannot be distinguished. In

all generations rnortality rate increases after these peri-ods prol:ab1.y

because of the enel:gy balance becoming irrcrea.s1ngly negative due to poor

assimilation. the death of ovigerous fetnal.es coincides lrith thi s increase

suggesting that egg production taxes the energy supply'. Sometimest

êegocohort6inPinkrmortalityisvirtuall¡'ç1ott"*ant'i'hroughoutthelife

of the generation iurplying that generally tlte enr,'irorruen'u cf tÌiese saline

lakes is not optir.al for B*-åi€ig!gg.

Of course, the switch frour positive to negat,ive energy balance

i-s not as precise nol as invariable as shown in Fig.2/¡. ft' r.rill rlepend

on assiniilation efficiency ancl the prevai)-ing ternpe::a.ture ancl salinity.

Changes in these last tr¡o will al-ter the intercep'b (but not the slope)

of 'uhe respiration line in Fig. 2/+i as shown p:reviousl.¡' (chapter 7)

they shor.r-ld. have little effect on ilgestion"

For recently hatched P. zie_tZ.!a4g to suz'vive it seems tteüessâl:)'

for them to use another source of energy. Undoubteclly the nauplii can

sr¡rvive for so¡ue t,ime on yolk reserves, but fol them to grow pa's'L this stage

they rmst eat. I'rom ol¡servation their guts rareJ-y contai-ner-1 seCilnent,

but r¡ere often coloured red. Hussalny (tglZ) suggesbecl tìrat tlte oralge .

pigment of the coltepod Calarqoe.g.i-a clltj.}la-ia frorn nearby Lake tno'¿.1-li

was derived. from pink autotro;¡hic sulphur bacterj-a. If these al-so exist

'in Pirrk arrd. CnndaTet P¿Mna nauplii may be able to ingest and'

assinilate then efficiently. They rnay al-so rely on printary production.

Ho.hrever, this is 1or¡ and rrnpredictable" If it i-s also hetercgenecusly

distribu-ted. r"¡ithin a lake then survival of young shrinç rnay well be pureiy

fortuitious.

L2l.

Àfurtherpossibilityistha.bthesÌopeofthefeetlinglinein

Fl'g.2A. d.eoreases after 0.2 rng (the lor'rest weight at r¡hich ingestion t'tas

nieasurecl). ff at the sane point the slope of the respiration line increases

-bhen there l¡ouÏl be a r,¡ider scope for positive energr balance' Eliassen

(tgsz) found an increase from 0.60 to 1.OO below a. dry welght of about 0'1

rng for A. salina. llithout detailed measurements at these srnall sizes for

P. zi it is inpossible to ccrnnent further' lJor'rever, a reasonable

conclu-sion from +.he present data is 'bhat the larger the shz'imp the more

Iike1y it is able to at least ingest sufficient energy fron the organic

matter in the sediment.

Di-scussion

There is no ooubt about the inrportance of the sediment in the diet

ofE-@.Primaryprod-uctioninPinkI^akeasmeaSured.sofar(r¡sc or approxirnately 56/+roooi *-' yt-t) only equals 35{l" of annual

ass.i,rnilation; this is most probabJy an over'-estjnate. Therefore the

shz'inrp rnust rely on the organic matter in the secirnent as an energy

souïce. Thej-r ability to assimilate 'Lhis governs their survival more

than anything e1se.

Asshowninchapterd,clutchsj.zeandrecruitmentwerevery

varj-able.Clutchsizedoesnotcorrelater^rithsalinity,temperature,

population density or size of animal r,rittiin either 1alçe and recmitment

shor^¡s no inverse relation with the size of the pzirent generation; in

fact,, for the d.ensities encountered it vari-es directly r^rith the mrmber of

temales becoming ovigerous" Growth rates, although variable, r;ere not

affected by tenperature or salinity. Turnover ratios (p/g) r¿ere not

constant; j-t llould be impossible to predict production from an estinate

of nea¡t bio¡nass. Therefore there appears to be no close lnternal

regulation of these processes by the shrimp nor environmental control

and the 1Í.ke1y explanation of this va::iabilit¡' is that it reflects varj-a-i;j"ons

]'.22.

in the assi.mi1a',,ion effj-ciency of !. zipiZíare. There does not appear

to be an absolute lack of food. leading to competition as the caloric value

of mud. saroples was fai-rIy constant inplying microbial production coulcl

offse'r, grazing.

The lack of i¡flexion in the gror.rLh curves probably results from an

inereased. potential for growth as size lncreases.rather than a rela;etion

of conpetition as population clensity d'ecreases. Ingestion increases with

weight at the sarne rate as egestion (Figs. 22 anð' 23), b:ut' faster than

respiration (fig. 2Z*). Thus assinilatj-on efficiency is constant uithin

a generation r¿h1le the relative availability of energy- for grouth instead

of metabolisn increases. The low variabillty of clutch sir'e (! ]]g"1

approximately) at one period of recruj-tment is perhaps indicative of a constant

percentage assinil-ation"

As mentiorred in chapter /e gror,rth is exporrential and thus relative

growth rate r¡ithin a generation is constant. Energ¡ shol:tage through

poor assinilation must affeet the relative grot,rth rate of indiuiduals,

but this is not d.istingu:ishable from the gror'rbh curves of a cohort because

these are derived from the nean size of survivors. However, betr'reen

generations there are detectable differences in this rate (and in the mean

clutch size) r¡hich reflect di-fferences in assj-nilation efficie'cy an¿

perhaps ultinat,ely in the degree of microbial productivity.

Betl¡een the populations in the tvo lakes there are also differences

ín gror.rth and more importantly in mr¡rbers of sl;rimp. Production and

assimilation rates of P. zieLziana are higher in Pink than in Cund,are.

îhe caloric value of the sediment in Cundare is smaller inplying that the

difference is caused by less abu¡rdant food not less efficient assinilation'

This is not une4pected. because animal numbers rrust ultina'bely be controllecl

by the productivity of their ecosystem; but it is improbable that this

ts the immediate influence regulating prod-uction r^rithin a populatj-on'

123"

The rate of faecal pellet production is also less in Lake Curdare

(fig. eZ). Accep'bing siurllar assinilation efficiencies this indicates

that the rate of energy uptake i-" lor¡er because it is rnore dÍlute. The

higher avcrage clutcli size of P" zietziana and the presence of larger

specimens in Lake Cu¡dare can probably be e;çlained by a lor+er average

salinity ra.ther than by an increase in assimilation efficiency. At a

louer salinity less energy is requi.red for respiration, as sholrn in chapter

5, and therefore of a fixed arnount ¿ssimilated more is av¿rilable for

prodne'r,ion of biomass either as individ,ual grovth or eggs. This

correla-r,ion only seems to exist bett¡een the tr¡o populations, not within

them, suggesting it is a long term response to a particular salini-ty ::ange.

Geddes (f973, 1976) ho',rever, noted an inverse correlation of P. zietziana

length r¡ith salinity for specinens talcen in different lakes or the sarne

lake at differen'b times. He also shot¿ed a lol¡ positive correlation betr¡een

clutch sj-ze arrd length of ovigerous female; the largest femaleÍì lrere founC

at the lor¡est salinity.

llhether or not such correlations are significant, differences

in clutch size or maxi¡rurn length have no d.etectable influence, a*u leas6

in my lakes, on net gror.rbh efficiency (Pft\). The same range of

values I5-3O/" (TaUles 2"1 and.2B) prevails in both lakes, auC there

appears no correlation betl¡een efficiency and salini-ty r.¡ithin a popu-lation.

Considering ',,he large variabi lity in the production and respiration esti-ma'r,es

meaningful differences in efficj-ency probably do not exist. Daborn (f975)

fonnd, values of 23 and 3311 for male and female, respeetively, of the

predator Ed.!,gg. Thi.s l¡as based on enerry budgets for inclividuals in

the wild rather than populaiions, tire higher value for females being d.ue to

production of eggs. Sushchen,u*a (f962) with À. salina raised in the

laboratory on algae recorded net grolrbh percentages of 24. to 277" for a five

fo1d. increase in food concentratÍon" Both these rcsults agree well uith ny

average efficiency (exolud.ing the snal1 values) of 23/".

LU"

Over the same change Í-n food concentration Sushchenya found a Ero,ss

growth efflciency (P/C) of 9 Lo I9/"t the highest percentage being ab -r,he

lowest coneentra'r,ion. Reel'e (Lor63 d) also noticed this for A. sal-itg,

but his average efficiency uas 25"/, and his maximum vas 79/"i efficiency

varied r,¡ith salinity, temperature and food concentration and generally

r,ras lrighest r.¡hen the fastest gror,rth occur::ed. I4ason (f9Ø) on the

contrary on1lr ¡o*rd values of Ä, to 5%. Dabornrs values were 1? and,3I%

for nale and fernale å-Á,jf,qÊ., respectively, and nr¡' values approximately

estimated from TabIe 29t assruing the same ratio betueen respiration and

production as in cohorts 5, 6 and. ? of Table 27, a-re 5-L27". these apply

to the population as a whole; individual P" zi.cLziana unable to meet their

cnerÐ/- demands i.¡ould not be gror,ring. Both these efficiencies (f/tt, f/C)

are cu¡nulatj-ve obscuring r,¡ide fluctuations during the life cycle. They

plobably reach a naximum r¡ith matute P. zietzianq because of e>çonential

gror.rth.

Despite this its gross growbh efficiency is 1ow. Although the

other values are largely derivecl from cultured populations r,¡ith abundant

supplies of food, the comparison is sti1" useful. It probably reflects

the d.ifficulty P. zi-etzj.ana experiences in neeting its energy de¡nands from

ingestion of the avaj.lable sediment. Because .>f vari-ab1e assimilation

effi-ciencies indivi-d'uals may quite often otrl¡r ¡s able to extract enough

enersr for resplration but not grot+th. This view i-s supported if the

annual estimates of producti-on and respiration in 'ooth lalces &re compared

with the regression line Melieill and lar"¡ton (fçZO) calculated from a

nr:r¡er of studies relating the logarith-ms of these two valu-es for short

lived poikilotherms ( -2 years). Taking J-og P as the independent variable,

in both cases the regression seriously u¡rder-estinates the amoun'', of

respiration. This i-roplies that compared with other studi-es the anount of

enerry stored as prod.uction by P. zig-lziana is very lot^¡ for the amount respireo.

L25.

Therefore there is some independent confirmation for the conclusj-on

thatthesurvj-va1o1Winthese1akesdepend.s1arge1yorrtheir,

ability to assirLilate the organic matter present in the Êediment. In

a rnore complex ecosysten it would be difficult to be confident of such

a conclusj-on because of the influence of predators and. possible competitorS.

Their apparent absence in sinple commu¡rities makes the analysis of energ-r¡

flor¿ tbrough salt lakes particularly worthwhile.

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