W&M ScholarWorks W&M ScholarWorks

Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects

1982

Zooplankton communities in Chesapeake Bay seagrass systems Zooplankton communities in Chesapeake Bay seagrass systems

Cathy Elizabeth Meyer College of William and Mary - Virginia Institute of Marine Science

Follow this and additional works at: https://scholarworks.wm.edu/etd

Part of the Marine Biology Commons, and the Oceanography Commons

Recommended Citation Recommended Citation Meyer, Cathy Elizabeth, "Zooplankton communities in Chesapeake Bay seagrass systems" (1982). Dissertations, Theses, and Masters Projects. Paper 1539617528. https://dx.doi.org/doi:10.25773/v5-b7ah-gh20

This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact scholarworks@wm.edu.

ZOOPLANKTON COMMUNITIES IN

CHESAPEAKE BAY

SEAGRASS SYSTEMS

A Thesis

Presented to

The Facu lty o f the School o f Marine Science

The College o f W illiam and Mary in V irg in ia

In P a rt ia l F u lf i l lm e n t

Of the Requirements fo r the Degree o f

Master o f Arts

by

Cathy E. Meyer

1982

APPROVAL SHEET

This thesis is submitted in p a r t ia l fu l f i l lm e n t o f

the requirements fo r the degree of

Master of Arts

Approved, June 1982

Herbert M. Austin

George C .^ ra n t

/ 2 'e& & J L J .Richard^L^ Wetzel ~~ 0

____Evon P. R u z e c k i 2

Assistant Professor of Oceanography Oregon State U n ive rs ity School of Oceanography Marine Science Center Newport, OR

George m BoenTert

TABLE OF CONTENTS

PAGEAcknowledgments .................... iv

L is t o f T a b le s ........................ v

L is t o f F ig u re s ............................................................................................... vi

A b s t r a c t ...............................................................................................................v i i i

I n t r o d u c t io n ......................................... 2

M ateria ls and Methods ................................................................................... 5

ResultsHydrographic D a ta .................................................................. 13B iom ass.......................................................................................... 16Abundance and Species Composition ...................................................... 19

Holoplankton . . . ~...................................................................... 28Meroplankton ........................................................................................... 35Demersal Plankton . ............................................................................... 44

Die! V a r i a b i l i t y ....................................................................................... 54

DiscussionCommunity Seasonality ............................................................................... 61Zooplankton Biomass ................................................................................... 63Holoplankton ............................................................................................... 65Meroplankton ............................................................................................... 68Demersal Plankton ....................................................................................... 71D ie l A v a i l a b i l i t y ....................................................................................... 78Summary.................... 80

C o n c lu s io n s ........................................................................................................ 82

A p p e n d ix ............................................................................................................ 85

L ite ra tu re C ited ........................................................................................... 87

V i t a ......................................... 96

i i i

ACKNOWLEDGEMENTS

I am g re a tly indebted to Dr. George Boeh le rt, who o r ig in a l ly

suggested th is p ro je c t to me and conceptualized a large pa rt o f i t ,

inc lud ing the gear design. To Dr. George Grant and Dr. Herbert Austin

(co-major professors) I g ive many thanks fo r th e ir con tinua l support

throughout th is study and fo r th e ir ac tive involvement in my o ve ra ll

education. A lso, thanks to Dr. Richard Wetzel and Dr. Evon Ruzecki fo r

c o n tr ib u tin g th e ir time and e f fo r t to the betterment o f th is study.

I re lie d on many in d iv id u a ls fo r th e ir help in f ie ld sampling and

labo ra to ry ana lys is , specia l thanks to Hugh Brooks, Deane Estes, Tom

Munroe, Mary Ann Vaden, Mike Rathbone and Mesonie H a iley.

Michael Vecchione, Laura Murray and Robert M iddleton provided many

hours o f s c ie n t i f ic debate, specu la tive op in ion , and miscellaneous BS,

a l l o f which aided in my growth as a person and a s c ie n t is t .

Deanne B o n v illa in sing le-handedly typed d ra f t a fte r d ra ft (a fte r

d r a f t ) , I am very g ra te fu l fo r a l l her assistance.

To my parents, fo r th e ir encouragement and enthusiasm towards a l l

my goals past, present, and fu tu re I am extremely th a n k fu l.

Joseph Lascara provided a l l the ingred ien ts to the recipe which

maintained my sa n ity throughout th is study: love, understanding,

advice and humor.

And, of course to Damon D e lis tra ty many thanks, w ithout his legs

th is thes is would not be where i t is today.

iv

LIST OF TABLES

Table Page

1. Temperature (°C ), s a l in i t y (pp t) and d issolved oxygen(m g / lite r ) by s ta t io n , March 1979 through A p r il 1980 . . . . 14

2. Mean zooplankton ash-free dry weight (mg/m^) by s ta tio n and the v a r ia tio n between s ta tio n s each month expressed as a percentage o f (h igh-low va lue )/h igh value fo r March1979 - March 1980 17

3. C heck lis t o f species id e n t if ie d and months o f occurrencefrom zooplankton c o lle c t io n s , March 1979 - A p r il 1980 . . . 20

4. L is t o f the three num erica lly dominant taxa and percento f numerical to ta l by s ta tio n fo r zooplankton c o lle c tio n s March 1979 - A p r il 1980 30

5. Day versus n igh t taxon abundance values (number per m^)by s ta t io n , May 1979 ......................................... 56

6. Day versus n igh t taxon abundance values (number per m^)by s ta t io n , August 1979 58

7. Day versus n igh t zooplankton ash-free dry weight values(mg/nr) by s ta t io n , May and August 1979 59

8. C h a ra c te r is tic zooplankton species from the two semi-annualassemblages: w in te r-sp rin g and summer-fall ............................. 62

9. Average abundance (number per m^) o f adu lt A ca rtia tonsaand Ac a r t i a c la us i in M a r c h ................................................................... 67

v

LIST OF FIGURES

Figure Page

1. Location o f study area in lower Chesapeake B a y ..................... 6

2. Sampling s ta tio n s at the Vaucluse Shores study s ite . . . . 7

3. Pushnet sampling apparatus. A. Frame dimensions.B. Schematic diagram . ................................................................... 9

4. Mean monthly surface values averaged over the Vaucluse Shores study area March 1979 - A p r il 1980. A. TemperatureB. S a l i n i t y .....................................................................................................15

5. Mean monthly values o f ash-free dry weight (mg/nr*) bys ta tio n (March 1979 - March 1980) 18

6. Monthly re la t iv e percentages o f ho lop lankton, meroplanktonand demersal plankton by s ta t io n , March 1979 - A p r il 1980 . 27

7. Mean monthly abundance (log[(number per m^) + 1 ]) o fto ta l copepods by s ta t io n , March 1979 - A p r il 1980 ................. 32

8. Mean monthly abundance (log[(number per m^) + 1 ]) of to ta l polychaete larvae by s ta t io n , March 1979 -A p r il 1980 .................................................................................................... 36

9. Mean monthly abundance (log[(number per m^) + 1 ]) o f to ta l barnacle larvae by s ta t io n , March 1979 -A p r il 1980 .................................................................................................... 38

10. Mean monthly abundance (number per m^) of to ta l decapod larvae and number o f species by s ta t io n , March 1979 -Apri 1 1980 ................................. 40

o11. Mean monthly abundance (number per m ) o f to ta l A. Fish

eggs B. Fish larvae by s ta t io n , March 1979 - A p r il 1980 . 43

vi

Figure Page

12. Mean monthly abundance (number per m^) o f to ta l adu lt polychaetes by s ta t io n , March 1979 - A p r il 1980 .......................... 45

13. Mean monthly abundance (number per m^) of to ta l mysidsby s ta t io n , March 1979 - A p r il 1980 .................................................... 47

14. Mean monthly abundance (number per nP) o f to ta l cumaceansby s ta t io n , March 1979 - A p r il 1980 .................................................... 49

15. Mean monthly abundance (number per m^) o f to ta l amphipodsand number o f species by s ta t io n , March 1979 - A p r il 1980 . . 52

vi i

ABSTRACT

Zooplankton abundance, species com position, and community biomass were determined in a lower Chesapeake Bay seagrass meadow and an adjacent unvegetated area. Sampling was conducted at n igh t monthly from March 1979 to A p r il 1980 and during the day in May and August 1979 using a bow-mounted pushnet rigged w ith two-18.5 cm nets (0.202 mm mesh). Data were analyzed tem pora lly , in terms of seasonal and d ie l a v a i la b i l i t y , and s p a t ia l ly , in terms o f vegetated versus unvegetated areas.

The zooplankton assemblage consisted o f o b lig a te (h o lo - and mero-) and fa c u lta t iv e (demersal) p lank ton ic forms. Two d is t in c t seasonal communities were id e n t if ie d , a w in te r-sp rin g assemblage peaking in March and a summer-fall assemblage peaking in August. Holoplankton, predom inantly calanoid copepods, accounted fo r 70-90% o f thezooplankton to ta l o f both assemblages.

D ie l changes in zooplankton abundance varied among taxa.Copepods, most demersal taxa , and the larvae of f is h , polychaete and pelecypod species were more abundant at n igh t compared to day c o lle c t io n s , usu a lly by 1-2 orders o f magnitude. Barnacle, gastropod, and decapod larvae abundances were s im ila r between d ie l periods.

Holoplankton and meroplankton exh ib ited l i t t l e s p a tia l v a r ia b i l i t y ; abundance and species composition were uniform between vegetated and unvegetated s ta tio n s . The ho lop lankton ic and mero- p lan k to n ic assemblages sampled in th is study c lo se ly resembledpublished d e sc rip tion s o f deeper, open water zooplankton populations inthe lower Chesapeake Bay. In c o n tra s t, demersal plankton defined in th is study as res iden t members o f the benthic substrate which emerge p e r io d ic a lly in to the water column, were more abundant and comprised a g rea te r percentage o f the zooplankton to ta l at s ta tio n s associated w ith seagrass. In p a r t ic u la r , s ig n if ic a n t ly higher numbers o f amphi pods, cumaceans, and isopods were co lle c te d in vegetated areas. Demersal taxa are im portant components o f zooplankton communities in sha llow - water seagrass systems.

Zooplankton biomass (AFDW) values were genera lly higher and more va ria b le than those reported fo r the lower Chesapeake Bay proper. W ith in shallow-water seagrass systems, conventional gross community biomass estim ates may not r e f le c t actual trends in s p a tia l or temporal d is t r ib u t io n o f zooplankton. D e tr itu s and tra n s ie n t demersal taxa may s ig n if ic a n t ly d is to r t community biomass values.

ZOOPLANKTON COMMUNITIES IN

CHESAPEAKE BAY SEAGRASS SYSTEMS

INTRODUCTION

Zooplankton com position, abundance and seasona lity have been

described and community s tru c tu re characterized fo r the lower

Chesapeake Bay in recent years (Jacobs, 1978; Grant and Olney, 1979;

1982). Using r e la t iv e ly large research vessels and standard sampling

gear, these stud ies were lim ite d to deeper, open Bay waters. The zoo­

plankton assemblage o f nearshore, shallow-water areas (<2 m) in the

lower Bay is poorly known, p a r t ic u la r ly in and around beds o f submerged

aquatic vegetation (SAV).

Studies conducted in North Caro lina estuaries have ind ica ted th a t

low standing stocks o f zooplankton are ty p ic a l fo r shallow embayments

(W illia m s , e t a l . , 1968). These authors concluded th a t the importance

o f zooplankton in the food chain decreases as the average depth o f the

water column decreases. This supports conclusions by Johannes e t a l .

(1970) and Glynn (1973) th a t l i t t l e energy inpu t is derived from zoo­

plankton w ith in h ig h ly p roductive shallow-water ecosystems. Conversely,

o ther researchers have v is u a lly observed swarms o f p lank ton ic organisms

(> 10^ in d iv id u a ls per m^), p a r t ic u la r ly copepods, over cora l reefs

and seagrass beds (Emery, 1968; Fenwick, 1978; Hamner and C arlton ,

1979) and concluded th a t zooplankton had been num erica lly under­

estimated and may represent a s ig n if ic a n t source o f energy to such

systems. In seagrass systems, wave energy and cu rren t v e lo c ity are

2

3

s ig n if ic a n t ly reduced by the p h y s ic a lly complex s tru c tu re o f the

seagrass blades (Wayne, 1974). Swarming or concentra tions o f a c tiv e ly

o r ie n tin g zooplankton may be fa c i l i ta te d by these hydrodynamic

changes.

Shallow-water zooplankton communities are characterized by

o b lig a te (h o lo - and meroplankton) and fa c u lta t iv e (demersal p lankton)

components (Emery, 1968; Sale et a l . , 1976; A lldredge and King, 1977).

Swarms or high dens ity aggregations are predominantly composed o f

o b lig a te zooplankton species. Most o b lig a te p la n k te rs , inc lud ing

copepods, cladocerans, and many species o f decapod zoea, o r ig in a te in

deeper adjacent waters and are not res iden t members o f the shallow -

water community (Hobson and Chess, 1978; 1979). Certain taxa

t r a d i t io n a l ly regarded as res iden t members o f the benthic substra te

( i . e . amphipods, cumaceans, polychaetes) emerge p e r io d ic a lly and move

in to the water column, e s p e c ia lly at n igh t (P orte r and P o rte r, 1977;

McWilliam et a l . , 1981). These fa c u lta t iv e forms, or demersal

p la n k te rs , e x h ib it d ie l v e r t ic a l m igra tion patte rns which are species-

s p e c if ic (A lldredge and K ing, 1980).

Both o b lig a te and fa c u lta t iv e zooplankters serve as prey items fo r

a number o f adu lt p lank tivo rous f is h species and other inve rteb ra tes

(Hobson and Chess, 1976; Robertson and Howard, 1978). In a d d itio n ,

s tud ies conducted in the Newport River estuary , North Carolina

demonstrated th a t zooplankton abundance may con tro l the su rv iva l o f

4

s p e c if ic p o s tla rv a l fish es during th e ir t ra n s it io n to ju ve n ile s (Thayer

e t a l . , 1974; Kjelson and Johnson, 1976). Since shallow-water seagrass

systems are considered im portant nursery grounds fo r a v a r ie ty o f

p o s tla rv a l and ju v e n ile fish es (Reid, 1954; K ikuch i, 1961; Carr and

Adams, 1973; Adams, 1976), the inpu t o f zooplankton may represent a

s ig n if ic a n t add ition o f energy to these areas w ith respect to the

feeding o f p o s tla rva l f is h e s .

The purpose o f th is study was to characte rize the general

zooplankton assemblage w ith in a shallow-water Chesapeake Bay seagrass

bed. The abundance and species composition o f o b lig a te and fa c u lta t iv e

zooplankton w ith in and adjacent to a bed o f submerged aquatic

vegeta tion were analyzed tem pora lly , in terms o f seasonal and d ie l

a v a i la b i l i t y , and s p a t ia l ly , in terms o f vegetated vs non-vegetated

areas.

MATERIALS AND METHODS

The study s ite was located on bayside Eastern Shore o f V irg in ia ,

approxim ately 37°25'N la t itu d e and 75°59'W long itude , in an area

lo c a lly known as Vaucluse Shores (F igure 1 ). A bed of submerged

macrophytes, 140 hectares in area, was p resent, bounded by land to the

east, a sandbar to the north and west, and the deep channel entrance of

Hungars Creek to the south (F igure 2 ). Vegetation maps of th is bed

(Wetzel e t a l . , 1981) ind ica ted the presence o f mixed stands as w e ll as

pure stands o f Zostera marina and Ruppia m aritim a. Dye stud ies

conducted in Ju ly 1978 p r io r .to the in i t ia t io n o f th is study,

demonstrated th a t flo o d in g water enters the bed from the deep channel

o f Hungars Creek, moving d ir e c t ly northward, then floods the shoaler

areas to the east (W etzel, pers. comm.). Water ebbs from the bed in

the opposite d ire c t io n ; average t id a l amplitude is about 1.0 m.

Two sampling s ta tio n s , designated nom inally as Ruppia and Zostera,

were estab lished w ith in the seagrass system. The nominal Zostera

s ta tio n was located at the southern end o f the bed, over a pure stand

o f Z. marina and was in clo.se p ro x im ity to the deeper channel o f

Hungars Creek. The Ruppia s ta tio n was positioned near the center o f

the bed over a mixed stand o f 1. marina and j*. m aritim a. This s ta tio n

was approxim ately 500 m north o f the Zostera s ta t io n , thus fu r th e r from

the deeper water channel and source o f flo o d in g water. Average high

5

6

Figure 1. Location o f study area in lower Chesapeake Bay.

FIGURE I

7

Figure 2. Sampling s ta tio n s at the Vaucluse Shores study s ite .SAV ind ica tes coverage by submerged aquatic vege ta tion .

0 II— I— I I— I v= mKilometer

= SAV

r i l lCO

I I I !

1 1 1 n ' i ' 1i 1111 I I I Ii 111111 ii 1111

i ii i l l1. rps

i: i: i: i: i: i: i! I)i! i! l! i l^ _ ^

111i : i ! i : i : ii1 1 1 'i11 i i i

h | I | 1 i i | I yji!i!i!i!i'iiiiinii.

111 j

Sampling Stations

R = Ruppia Z = Z ostera S = Sand

L l —76° 00' FIGURE 2

8

t id e depth was 1.5 and 1.2 m at the Zostera and Ruppia s ta t io n ,

re s p e c tiv e ly . A th ird s ta t io n , designated as Sand, was estab lished

approxim ately 800-1000 m west of the seagrass bed across the sandbar in

an unvegetated area; average high t id e depth was approxim ately >_ 2.0 m.

Monthly sampling was conducted at n igh t from March 1979 to A p r il

1980 at a l l three s ta tio n s during high t id e . The depth required fo r

gear deployment (minimum o f 1.0 m) necessitated sampling as close to

high t id e as poss ib le . The d iv e rs ity and abundance of zooplankton,

p a r t ic u la r ly fa c u lta t iv e forms is gene ra lly higher at n igh t (Robertson

and Howard, 1978; A lldredge and K ing, 1980), the re fo re sampling was

undertaken at n ig h t. In a dd ition day samples were taken during high

t id e in May and August 1979 to assess d ie l v a r ia b i l i t y .

Standard sampling gears such as towed, b rid le d nets are u n s a tis ­

fa c to ry fo r shallow-water environments ( M il le r , 1973). Turbulence

created by the vesse l, p ro p e lle r , and b r id le s may re s u lt in increased

gear avoidance by some organisms (K rie te and Loesch, 1980). In

a d d it io n , s i l t , d e tr itu s and vegetation may be suspended or dislodged

re s u lt in g in " d ir t y " samples which are q u ite d i f f i c u l t to analyze

q u a n t ita t iv e ly and may be "contam inated" w ith benthic organisms which

are also d is lodged. To avoid these d i f f ic u l t ie s a bow-mounted pushnet

(F igure 3) was u t i l iz e d (M erriner and Boeh le rt, 1979). The frame was

constructed of 1/2" diameter galvanized p ipe , rigged w ith a one-meter

ich thyop lankton net (0.505 mm mesh) and two-18.5 cm zooplankton nets

(0.202 nm mesh). Samples from the 0.505 mm ichthyoplankton net were

analyzed by J. Olney (VIMS) and the data presented in Brooks et a l .

9

Figure 3 Pushnet sampling apparatus. B. Schematic diagram.

A. Frame dimensions.

110c

m

T ■70 cm

230cm

10

(1981). One o f the 0.202 nin zooplankton samples from each tow was used

fo r taxonomic a n a lys is , the o ther fo r biomass de te rm ina tion . The le f t

zooplankton net was equipped w ith a ca lib ra te d General Oceanics

flowm eter to q u a n tify volume o f water f i l t e r e d ; i t was assumed th a t

both zooplankton nets sampled equal volumes. Averaged over the study

p e rio d , the mean volume o f water f i l t e r e d by a zooplankton net was

5.77 m (+ 1.7m^ standard d e v ia tio n ) during a 3-minute tow.

The pushnet apparatus was deployed over the bow' o f a 5.8 m o u t­

board c ra f t and pushed fo r three minutes at a boat speed of

approxim ately 1.5 knots (2 .8 km /hour). The zooplankton net fished at a

depth o f 1-meter from the su rface , w hile the ich thyop lankton net fished

the e n tire area surface to 1-meter deep (F igure 3 ). During periods of

high ctenophore abundance, tows were reduced to two minutes to decrease

c logg ing . Two re p lic a te s were taken in each h a b ita t each month. The

presence o f the she lled gastropod, B itt iu m varium, in e ith e r o f the

nets a fte r a tow ind ica ted th a t the nets had brushed attached liv e

Zostera or Ruppia. Such samples were considered contaminated and

d iscarded. The depth o f the net was then ra ised and the tow repeated.

The le f t zooplankton net sample was rinsed w ith d is t i l le d water,

placed in a w hirlpak bag and frozen on dry ice to be used fo r biomass

a n a lys is . In c id e n ta lly co lle c te d pieces o f dead Zostera , flo tsam , or

o ther nonbio lo g ic a l m a te ria l was removed from biomass samples in the

f ie ld p r io r to the treatm ent described above. The other sample was

preserved w ith 5% buffe red fo rm a lin fo r fu tu re taxonomic an a lys is .

11

Between re p lic a te s at each s ta t io n , water was co lle c te d by bucket

fo r surface measurements o f tem perature, s a l in i t y and d issolved oxygen

(DO). Temperature was measured w ith a mercury thermometer. S a lin i ty

and DO b o tt le samples were returned to the lab and analyzed using a

Beckman Induction Salinometer and a M odified W inkler T it r a t io n method,

re s p e c tiv e ly . Water depth was recorded p r io r to each tow.

In the la b o ra to ry , biomass samples were lyopho lized , weighed,

ashed in a m uffle furnace at 500°C fo r f iv e hours and reweighed. Dry

w e igh t, ash w e ight, and ash-free dry weight were determ ined. The

taxonomic samples were i n i t i a l l y sorted fo r a l l ra re , gen e ra lly la rge r

organisms. For sm a lle r, more abundant groups, each sample was q u a n ti­

ta t iv e ly s p l i t using a VIMS s p l i t t e r (B u rre ll e t a l . , 1974) in to

successive ly sm aller a liq u o ts . Between 100-200 in d iv id u a ls o f each

major taxonomic group were so rted . Specimens were la te r id e n t if ie d to

the lowest taxon p o ss ib le , in most cases to species. Major taxonomic

references used in the id e n t if ic a t io n s are presented in an Appendix.

Abundance data fo r each sample were standardized to the number of

in d iv id u a ls per m o f water f i l t e r e d , and biomass was standardized to

mg ash-free dry weight per m^. R eplicate values were averaged to

obta in a mean s ta tio n value each month. In the case o f a missing

re p lic a te , the s in g le tow value was presented as the mean. Log tra n s ­

formed (log^g X+D abundances were ca lcu la ted fo r separate analyses

o f some o f the more abundant taxa.

12

Each id e n t if ie d taxonomic group was placed in one o f the fo llo w in g

ca teg o ries : ho lop lankton, meroplankton, or demersal p lankton.

Abundance and numerical percent o f to ta l zooplankters were determined

fo r the three components and selected taxa. S p a tia l and temporal

trends in abundance v a r ia b i l i t y and gross biomass v a r ia b i l i t y were

examined g ra p h ic a lly . The Wilcoxon signed-rank te s t was used to te s t

fo r s ig n if ic a n t d iffe re n ce s in mean values between s ta tio n s over the

14-month study pe riod . This is a nonparam etric, d is t r ib u t io n - f re e

procedure which incorporates magnitude as w e ll as d ire c tio n of

d iffe re n ce s between paired values (S ie g e l, 1956; Hollander and Wolfe,

1973); only two s ta tio n s may be compared at a tim e. The n u ll

hypothesis was th a t no s ig n if ic a n t d iffe re n ce s existed between

s ta tio n s . S ign ifica n ce was chosen to be the alpha = 0.05 le v e l, using

a tw o -ta ile d te s t .

RESULTS

Eighty-one n ig h t and twelve day zooplankton samples were co lle c te d

between March 1979 and A p r il 1980. R eplicate tows at each s ta tio n were

su cce ss fu lly completed monthly w ith the fo llo w in g exceptions: on ly one

tow fo r the Sand s ta tio n in March 1979 and Ju ly 1979 and one tow at the

Ruppia s ta tio n in November 1979. Rough water associated w ith strong

northwest winds delayed the October sampling u n t i l the f i r s t o f

November. L ikew ise, February sampling took place on the seventh o f

March due to a severe w in te r storm at the end o f February.

Hydrographic Data

Surface water temperatures fo r th is shallow -water system were

h ighest in Ju ly (28.0°C) and lowest in February (1.5°C) (Table 1 ).

S a l in i ty ranged from 15.2 ppt (A p r il) to 23.0 ppt (August) and

d isso lved oxygen varied from 6.6 m g /lite r to 12.6 m g /l ite r (Table 1 ).

Water temperature increased and decreased maximally between March and

A p r il (+7.0°C 1979, +10.5°C 1980) and November and December (-8.0°C

1979), re s p e c tiv e ly (F igure 4A). S a lin i ty values were high through the

summer then decreased 6.0 ppt by m id - fa ll (F igure 4B). E rra tic

temporal changes in surface s a l in i t y were also apparent, p a r t ic u la r ly

during spring months, co inc iden t w ith loca l f lu c tu a tio n s in ru n o ff. In

genera l, d isso lved oxygen was in ve rse ly re la ted to temperature. Low

hypoxic DO values (<3.0 m g / l i te r ) were not observed during th is study.

13

Table 1. Teiperature (°C), sa lin ity (ppt) and dissolved oxygen (mg/liter) by station, March 1979 through A pril 1980.

MONTH RUPPIA ZOSTERA SAND

°C ppt ng/1 °C ppt ng/1 °C ppt ng/1

1979 MARCH 8.0 17.7 12.6 8.0 17.4 12.6 8.0 17.3 11.8

APRIL 15.0 18.5 9.6 15.0 18.5 9.6 15.0 18.5 9.6

MAY 21.5 16.9 7.8 21.5 17.0 8.7 21.5 17.6 9.1

JUNE 20.6 20.0 8.3 20.8 20.0 6.6 20.8 19.0 7.1

JULY 27.0 15.8 8.9 27.0 15.3 8.9 28.0 15.2 *

AUGUST 23.4 23.0 7.7 23.4 23.0 7.3 23.4 23.0 8.5

SEPTEMBER 21.0 21.0 7.8 21.0 20.8 8.7 21.0 a . 6 8.0

OCTOBER 15.0 19.3 8.5 15.5 19.2 8.4 15.5 20.5 *

NOVEMBER 12.5 16.4 12.0 12.0 17.0 11.1 12.0 16.8 11.1

DECEMBER 4.0 ★ ★ 4.5 •k * 4.0 * *

1980 JANUARY 5.5 * ★ 5.5 * * 5.5 * *

FEBRUARY 2.0 18.8 11.4 2.0 19.0 11.7 1.5 19.0 H .8

MARCH 7.5 20.9 11.2 7.0 20.8 10.5 7.0 20.8 10.5

APRIL 17.5 15.2 9.7 17.5 15.2 9.7 17.5 15.2 9.9

1979 MAY DAY 21.5 16.6 8.3 21.5 17.2 9.9 21.5 17.6 10.2

AUG DAY 23.4 22.7 7.3 24.1 23.8 7.7 24.4 23.7 8.5

* missing value

15

Figure 4 Mean monthly surface values averaged over the Vaucluse Shores study area, March 1979 - A p r il 1980. A. Temperature B. S a l in i ty ( * = missing values)

25

H

oCM 10 10 O O i CD K CDIO CM

CO

** Oo) 3yruvu3dW3± m (°%)AiiNnvs

FIGU

RE

4 19

79

1980

16

Values d if fe re d on ly s l ig h t ly or were the same between s ta tio n s on

each sampling date fo r temperature (<1.0°C ), s a l in i t y (£1.2 pp t) and

d isso lved oxygen (<1.7 m g / l i te r ) . No cons is ten t in te rs ta t io n pa tte rn

was evident fo r any o f these parameters. Day temperature, s a l in i t y ,

and DO values were very s im ila r to the n igh t observations at each o f

the th ree s ta tio n s . Therefore, these hydrographic parameters were not

considered im portant fa c to rs in flu e n c in g zooplankton d is t r ib u t io n

between the three s ta tio n s or zooplankton d ie l v a r ia b i l i t y during th is

study.

Biomass

Ash-free dry weight (AFDW) values o f zooplankton biomass ranged

from 29.2 mg/m^ to 783.0 mg/m^ (Table 2 ). No values are presented

fo r A p r il 1980 c o lle c tio n s due to problems w ith the m uffle furnace. In

54% o f the c o lle c t io n s , AFDW values were between 100-400 mg/m^.

Zooplankton biomass was highest in September (780 mg/m^); values >400

m g/nr were also observed in January (Ruppia, Zostera) and February

(Sand, Zostera) (F igure 5 ). A p r i l , June, and November were charac­

te r iz e d by low AFDW values (<100 mg/m^) at a l l three s ta tio n s .

In genera l, mean AFDW values d if fe re d between s ta tio n s by g rea te r

than 100 mg/m^ w ith a maximum d iffe re n ce of 500 mg/m^ (February).

Expressing the d iffe re n ce between s ta tio n high and low AFDW estimates

in any month as a percent o f the high va lue, s p a tia l v a r ia b i l i t y ranged

from 31.4% (November) to 90.0% (December) w ith a median o f 53.9%.

However no con s is ten t in te rs ta t io n p a tte rn was e v iden t. S ta t is t ic a l

17

Table 2. Mean zooplankton ash-free dry weight (rrg/n^) by stationand the variation between stations each month expressed as a percentage of (high-low value)/high value fo r March 1979 - March 1980.

STATION

Month Rippia Zostera Sand % Variation

1979 March 225.3 129.3 234.2 44.8

April 69.3 35.1 39.8 49.4

May 397.5 132.4 118.6 70.2

Jine 91.7 61.4 32.1 65.0

July 380.6 151.8 164.5 60.1

August 121.3 163.9 253.5 53.9

September 783.0 668.6 432.3 44.8

October 57.8 92.4 269.5 78.6

November 48.4 70.6 51.1 31.4

December 29.2 292.5 47.8 90.0

1980 January 492.4 449.4 232.9 52.7

February 170.2 424.5 681.0 75.0

March 316.2 338.7 167.8 50.5

18

Figure 5 Mean monthly values o f ash-free dry weight (mg/m^) by s ta t io n , (March 1979 - A p r il 1980). (R = Ruppia, Z = Zostera, S = Sand).

800

nCO

t r

coINIcr

co

co(si

co

co

co

co

rsi

co

INI

Oo o

oCO

ooIf )

oo

oorO

OOOJ

oO

CO

( £ uu/6ui) M O J V

FIGU

RE

5 19

79

1980

19

ana lys is using the Wilcoxon te s t ind ica ted no s ig n if ic a n t d iffe re n ce in

mean zooplankton biomass between s ta tio n s over the th irteen-m onth

p e riod .

V a r ia b i l i t y between re p lic a te AFDW values by s ta tio n were also

determined as a percentage. In genera l, percent v a r ia tio n between

re p lic a te s was low and s im ila r at a l l s ta t io n : Ruppia, 2-48% median »

25%; Zostera, 7-51% median = 24%; and Sand, 11-75% median = 27%.

Abundance and Species Composition

A to ta l o f 124 species was id e n t if ie d from 81 n ig h t c o lle c tio n s

over the 14-month study pe riod . Occurrence o f species by months is

presented in Table 3. The zooplankton assemblage consisted o f o b lig a te

(h o lo - and meroplankton) and fa c u lta t iv e p lank ton ic forms (demersal

p la n k to n ). Holoplankton was the num erica lly dominant component (F igure

6 ) and included species o f copepods (ca lanoids and cyc lo p o id s ),

cladocerans, chaetognaths, r o t i fe r s , cn idarians and ctenophores. The

meroplankton component ranked second num erica lly and consisted o f f is h

eggs and la rvae , decapod zoea, and larvae o f gastropod, pelecypod,

phoron id , polychaete and barnacle species. Demersal p lankton , defined

in th is study as res iden t members o f the ben th ic -sub s tra te community

which emerge p e r io d ic a lly in to the water column (Hobson and Chess,

1976; Robertson and Howard, 1978), gen e ra lly represented less than 10%

o f the zooplankton numerical to ta l (F igure 6) . Amphipods, isopods,

h a rpac tico id copepods, cumaceans, tana ids , adu lt polychaetes and mysids

co n s titu te d the demersal component sampled in th is study.

Table

3.

Chec

klist

of sp

ecies

id

entif

ied

and

month

s of

occu

rrenc

e fro

m zo

oplan

kton

colle

ctio

ns,

March

197

9 thr

ough

Ap

ril

1980

. (H

= ho

lo-,

M =

mero

-, D

= de

mersa

l pl

ankt

on)

20

CO

C\J

CVJ

CTl

00

VO

LO

CO

COLUt—«a

§ i— izrO

8.aCOCO

CO Q .

S I2 1

rtJsO0 .0o’CO

£urO

&53tn*r—COa

03

8

QjfO.C

13<DqZ

COCD

■8

oco

Ll_ 3

s

X X X

X X

X X

X X X

X X

X X X X X

X X X X X X

X X

X X X X

'-■Sj

• ■O £ 3

crrosz$y)o

fT3■8

IM

s Glyc

era

dibr

anch

iata

Ne

reis

succ

inea

Pa

rahe

sione

sp

. Pa

raon

is fu

lgen

s Sc

oloplo

s sp

.

Table

3.

(con

tinue

d)

21

oo

o

to X X

TXTQ_

£

X X X

oo X X X X

CVJ X X X X X

X X X

CVJ X X

"8

X X X

oo X X X X

X X X X X X X

CT»&

LO X X

X X X X

CO X X X X

ooLUI— I

af t

Q .oo

oSI

^ I dI CO

S afc.b

8I£%

jC£a

$

<o

§ f t§ id

a

to >— ■8 .£ § 55CO

CO

1to3

to cS:"Q 3 .5 ,oito o

. c I

6 o

a8-

CO3

toCO

to

£

toCD

IcCDc_>

CO 3 o •§-c

+ J | C

CO

§I ;+->

S l

22

733C•r—

+->C

80

oo<v5

ro

C s J

C\J

15

oo

o

03

CT>

C O

V O

uo

oo

T I TQ _

ooLUI—H

hi05

X X X X X X

X X X X

X X X X

X X

X X

X X X

X X X X

X X X

X X X

X X

X

X X X X

X X

X X

X X X X

X X

03x> •on a.» on

ro on3M

•a ui fe_i Ci­

s_4 - >00

Si

■3< uo n

Q _

onon"IT onW•r*o $8 - g

3 cS

03onong

• o n Q J

a.'g-g1W o - _ O 03 ( D

s jb & £

a on aWD 1/1• o .-o cn"o•I— *r— * r - C r- C 3 «3 3

o

f Oaon3 3

• r “x : 3

s-CO

X X

X X X X

X X

X X X X

X X

X X

X X X X

X X

X X

X X

X X

X X

X X

X X

on3

03

o3 a) aj

a c c

T h hs _ C Q C Q•r—

X X

X X

X X

£ 03 E*

l l

a)

onaT3

El

J t con

X X

X X

X X X

X X X

X X X

X X X

X X

X X X X X

X X

onsC J

r 3>

y **Sj( o < 8Q J '—

s $3C_5

• uax;on

5•r—o

03

.3on

cou3

C/1•r*

5on£

o

Table

3.

(con

tinue

d)

23

X X X X X X X X

co X X X X X X X X X X X

CNJ X X X X X X

X X X X

CM X X X X X X X X X X X X X X X

X X X X X X X X X X X X X

■8X X X X X

oo

QX X X X X X X

00 X X X X X X X X X X X X X X

X X X X X X X X X

co X X X X X X X X X

<T>LO X X X X

X X

X X X

X X

CO X X X X X X

O .

£ o

ooIdLl I— •

af t &

o■s<uto

o _

fd•

Q.a; to8 •

X) X>fd *Es 3

03cL"8OO I—

•r“

£ «

& o s

03 -a

O l 23

CD

fd

to O

ai

fdC LQ .to

I C D

o to

a -s g

C D

. 8

E 5

rd4£fdr—

* 1U s-

1fd l to

X J 3s» £=lPfd

+ J•r—

£ 5 l £

to<u■g

toTIsfd

"aj§h

Q_

fdB-cE

5-scr

■§oo

a3■s

i

Table

3.

(con

tinue

d)

24

oo

CXI

C \ J

■ 8

oo

3C3cr»

oo

C O

cr>LO

OO

TCT

OOLUi— i

aft

X X

X X X X

X X X

X X

X X

X X

X X X X X

X X X X X X X X X X X X X X X X X X

X X

X X

X X

X X

X X X X X

X X X X X X X

X X X X

fdh

CL CO _S 8-5! "I— • I— <us_ -o sd s- &s a- s i 5 o °

CO

co 3

C/1<O Q T 3

fd ctj g j"8 8

8 - . -M T 3

CO

a-fdC/1 8

f d §

"8 ?= 8' ,fdQ

p 8(7) c/i fd coC/l OJ

id T3"o

B N+->

§ *

CO 3ao$ s_

c/l cd

§

coCDX3Oco

S-• o8 * <d

o

8X&CL)

a

<d

aa .

oC L |

C/l3S _3

aQ _

a +3CO C/l

^ ■ e

CO

Ifd a .

C/l3

to §3 2? §y +-> i

fd CO 3= O U•r“

&C/lCOa?

CO 4->2

fd JBJB 22X +■> +■>•r- O o fd£= esz £= c CO•r- • r—

c *Q_ Q . Q_

Table

3.

(con

tinue

d)

25

oo

C \ ]

CVJ

■S

oo

€ cn

co

CO

L O

CO

£

ooU Jt— I

a05

X X

X

<S)E

I. fd

8:5co gj r ol S ’

2 \3

8>fe

c5 -a

X X X

X X X

X X X

815fd+->

s Soo

fd

81oo S’oo soo

XJc=3rd

soo

X X

X

X X X

X X

X X X X X

X X X X

X X X X X

X X X

• -p c l <yCO COCO

o

^ a)Q O QC CO

5 s1

CO3f — CO

* r *s

I E

£

£

f d

5

S F

E• E

wo

« d

o

£

8

1C Q

uCOo

3 > Hyps

oblen

nius

hent

zi Le

iostom

us

xant

huru

s Me

ntras

m

artin

ica

Micr

oqob

ius

thal

assi

nus

Micr

opoq

onias

un

dula

tus

Table

3.

(con

tinue

d)

26

CO X X

C\J

CVJ

*soo

QCT>

OO X X X X

co

cn&

in X X

CO

Cl .

O OLU»— i

05

CO3to+->CCD"O

(Ofe

cl.

o

coB

CDCO

- a“O 3 CDCO Q _

S-a

D _

CO3COO

• sCL fO CO

8 | 32 5S I j

CO3IS

O O

§«o

3

00B&

27

Figure 6 Monthly re la t iv e percentages o f ho lop lankton, meroplankton, and demersal p lankton by s ta t io n , March 1979 - A p r il 1980. (R = Ruppia, Z = Zostera, S = Sand).

>LU

<COtr

0 O' w j tr 5O W LlJ X S Q1 I I

y y v v y v y v > 8 '

i

CO

K ! \ \ a \ \ \ a \ \ \ a \ \ i\ ^\ \ \ \ \ \ \ V \ \ V \ x \ \ _ \ XX

COg? : ! \ \ \ \ \ " \ \ \x ^ x v O O O ^ O v X g

m S S S S B i S S S M S M B M ^ ^ S S ^ 2

Ir"

OO

To0>

T “ooo~T~o T ”o io

T "oIOT "o<■

"T“oIO

T "oCO

T "o

NOlllSOdlMOO ±N3DH3d

FIGUR

E 6

1979

19

80

28

Species composition and abundance o f each taxonomic group w i l l be

presented p h y lo g e n e tic a lly under the appropria te subheading ( i . e .

h o lo -, mero-, demersal p la n k to n ).

Holoplankton

C n id a ria . One species o f hydromedusae, Nemopsis bachei, was

co lle c te d in low numbers May through September 1979 and A p r il 1980.

Q u a lita t iv e ly , higher d e n s itie s were observed at the Ruppia and Zostera

s ta tio n s compared to the Sand s ta t io n . Two scyphozoan species were

recorded during th is study. Chrysaora qu inquecirrha occurred during

summer months w h ile Cyanea c a p il la ta was co lle c te d during the w in te r

months. N either species was present in numbers g rea te r than 1/m^ at

any o f the s ta tio n s .

Ctenophora. Ctenophores d is in te g ra te q u ic k ly when placed in

fo rm a lin , thus no e f fo r t was made to q u a n tify th e ir occurrence.

Mnemiopsis le id y i was c o lle c te d May through October 1979. Numbers were

g rea tes t during September, as evidenced by f i l l i n g 50% o f the e n tire

volume o f the net during a three minute tow. D ensities were

q u a l i ta t iv e ly observed to be h ighest at Ruppia and lowest at the Sand

s ta t io n . Another species, P leurobrachia p ile u s , occurred in January

1980 in r e la t iv e ly high numbers.

R o t ife ra . R o tife rs were present in March 1979 and A p r il o f both

years . An u n id e n tif ie d so ft-bod ied species comprised 1-4% o f the

zooplankton to ta l during March (580/m^). The c o n tr ib u tio n o f

29

r o t i fe r s to the zooplankton community was probably underestimated as

the net mesh used in th is study (0.202 mm) was too large to q u a n ti­

t a t iv e ly sample th is group.

Cladocera. Two cladoceran species were present in the summer-fall

c o lle c t io n s . Podon polyphemoides occurred in Ju ly 1979 w ith a maximum

abundance o f 1800/m^ (Zostera) representing 4% o f the zooplankton

to ta l at a l l three s ta tio n s . Evadne te rq e s tin a was observed in low

numbers Ju ly and August 1979. Another pulse in cladoceran abundance

(500/m^) was observed during A p r il 1980 accounting fo r 7% (Ruppia) to

27% (Sand) o f the zooplankton to ta l . Evadne nordmanni was the only

species recorded in these c o lle c t io n s .

Copepoda. Copepods were the num erica lly dominant and most d iverse

ho lop lank ton ic taxon sampled. A to ta l o f eleven calanoid and two

cyc lopo id species was id e n t i f ie d , representing nine fa m ilie s .

Calanoids and cyclopoids combined accounted fo r g rea te r than 85% o f the

zooplankton numerical to ta l in 7 o f the 14 months sampled (Table 4 ).

Copepods comprised less than 50% o f the zooplankton to ta l on ly in May

and June 1979 and A p r il 1980.

Abundance o f to ta l copepods appeared bimodal over an annual cycle

(F igure 7 ). D ensities g rea te r than 10^ in d iv id u a ls /m ^ were

observed in March o f both years and throughout the period Ju ly -

October 1979. These peaks in abundance re fle c te d the seasonal

succession pa tte rn in species com position. Two d is t in c t copepod

communities were apparent, a w in te r-sp rin g assemblage and a summer-

30

</>s1 11 15 sB J+-> Q-

I S£ s s(_) (O

• r - M i— S . I/ ) *r—

! - § > £ ■

fl3■8

cn

x : +-> j-+-> -C 1 4->Q J T J

j C O < n■*-* T %- cn

cu

5

H O Ot t H r —Icr>

8>bas as (V "8 a ju8-3= p 8-8 b

C_> Qd CQ

h • • •

CQ CO i—»

8>

££10(0 0!

"8 b J&*= K& g o

< _ > a c : q _

t— i cvj « v j- • • •

eg CO 00CXI

8

S ib

<T3 OJ CU" n <D r —

I t Icr o jo

C_> Q _ CQ

VO CO

S R 00

8S i■” b

<r* aj a)• n fO r—

s - t i <§■§£

CM CO 00

88 £b *- $& 8-gu jc o

i « iC Q Q . U

co 00 UO

8

s i^ SB£ - aj ro <u(T3 -r-j i—J C O U£ | | CL a CQ

8

s s s ^

■ S . S 8© y -C=8-g £ S' b 'oU CQ Q.

LT> LO CMQ * * VO

LO O «—•

W E

a! (O o

pb 8-8CQ O CD

CM CO 'O ’CO CO H CM CM CM

LO 00 CM • • • S - w w

8>b

« S’S"8 8 S’8 * - a £8 " r~— 8

u o a

LO CO "vf • • •

U C J C Q

COHN • • •

S ' r o

rs oo VO • • •

H CO CO cn

N CM CO • • •

8>b

'd* <n lo • • •

s>b

N L Q O

8>br*

to "8 S to S "8■8 a s "8 8 a

8 -5 8

cm cn in CMCVJ» 9 ^ cn cn*-J00

8>b

o " 8(O QJ -“8 8 5; 8*5 8 erJSaJo Z a .

Scn

Table

4.

(con

tinue

d)

31

CM 00

<0 CD <1£"3 <L> -r^

O CM 00CD ^ oo

r s l o v o

»>

<o "o S*8.8 a© ■ 'o

C_5 Q_ 2 1

co o r--

c n l o o o • • •cn cm

C O * 3 "• • •

g ) CM r H

<T3 <U

1— CO LO • • •

S? CM CM

Q_%Cd

o>

8>b

-3

8 'os #

O CQ Q .

O LO CO

g j d d

» S S *

- 3■s.a $ ® « - 5

-' J5 oO CO Cl.

cncn

<T3<o S 8^8 J « 0.-0 »

8 -8-

o 5. S'—r—

CM CM c o r^j d LO

it i itsS jo "8 <0 ^ 0.

S

8>fe

43 <S "jsj

I -8-J>oO t C L

r-l CO cn

s a d

>

££ «fa qj cp

■8 M 3

8-0 o o_ 2:

es

8

I

■8 S sO "goS '- H &3V5C_> 2 : Q-

co r s i H • • •

8S

fOcO -$

- 0 8 8O "go8--T2 £t # s

*

8>b

8> <ub 5

40 aj i j j ^ 8 . 2

£& £>ro c_> S a .

iD

$ - Its Q3 03 •n <0 1—0 jc : u

8 - 0 80 Q - C Q

CM CO LO r ^ .

^ CM d « ^

>c3

- 8 * 3

& o J ,C_5 O - 2 Z

8

es& -

<0 o> a>■3 5 ^ 8- H8 CL. CO

8eb

o

APRIL

Co

pepo

da

41.3

Cope

poda

42

.1 Co

pepo

da

32.3

Polyc

haete

lar

vae

18.1

Clad

ocer

a 25.8

Cl

adoc

era

27.2

Barn

acle

larva

e 16

.9 Ba

rnac

le lar

vae 1

6.5

Barn

acle

larva

e 17

.8

32

Figure 7 Mean monthly abundance (log [(number per m^) + 1 ]) o fto ta l copepods by s ta t io n , March 1979 - A p r il 1980.(R = Ruppia, Z = Zostera, S = Sand).

tnM <£ SL

~UTMcn

COTT~g~

coISI T

"S5""FTIE

coTTST

COTT~S1

o00cn

COTTJE.

CO

COTTcn

~VTTT

cncn

COTTSI

CONa:

rID ro 0J

coisiTT

CO

Cl + ( sui/x)J 6o|V Q 0 d 3 d 0 D aouDpunqv

UJ(T3O

33

f a l l assemblage. Low abundance (<10^ in d iv id u a ls /m ^) was

c h a ra c te r is t ic o f the t ra n s it io n months between the two seasons, spring

to summer (May-June) and f a l l to w in te r (November-December) .

S ta t is t ic a l ana lys is o f mean copepod abundance, using the Wilcoxon

te s t , ind ica ted th a t no s ig n if ic a n t d iffe re n ce ex is ted between any

s ta tio n p a irs (Ruppia-Zostera, Zostera-Sand, Ruppia-Sand).

Adults outnumbered copepodites in a l l c o lle c t io n s . However th is

is probably an a r t i fa c t o f sampling e rro r as the mesh size (0.202 mm)

used in th is study was too large to adequately sample the sm aller

in d iv id u a ls .

The w in te r-s p r in g copepod assemblage consisted o f A ca rtia c la u s i,

Ac a r t ia copepodites, Centropaqes hamatus, Eurytemora a f f i n i s , Oithona

s p ., Pseudocalanus m inutus, Temora lo n q ic o rn is , and A ca rtia tonsa .

According to Bradford (1976) North American specimens id e n t if ie d as A.

c la u s i (G iesbrecht) may be A. hudsonica p rev iou s ly known as A. c la u s i

hudsonica (P inhey). Bradford (1976) revised the subgenus A c a r t iu ra ,

e le va tin g hudsonica from subspec ific to s p e c if ic s ta tu s . She

determined A. hudsonica type lo c a l i t y as Patuxent R ive r, Md and the

G ulf o f Maine w ith A. c la u s i type lo c a l i t y as Genoa Harbor, I t a ly and

R iv ie re de M o rla ix , France. However th is re v is io n has not been w id e ly -

adopted by North American s c ie n t is ts . Throughout th is study, the

designa tion A. c la u s i w i l l be m aintained.

A c a rtia c la u s i and A ca rtia spp. copepodites co n s titu te d g rea te r

than 85% o f the March 1979 copepod to ta l . A ca rtia tonsa and £ . hamatus

34

were present in low numbers (less than 4% o f the to ta l each). In March

1980 a numerical peak in to ta l copepod abundance was observed; however,

the community s tru c tu re d iffe re d from th a t o f 1979. A ca rtia c la u s i was

not the dominant species nor had A. tonsa numbers decreased to the

le ve l observed in 1979. A ca rtia c la u s i represented less than 23% o f

the to ta l and A. tonsa > 27%. In a d d itio n , £ . hamatus and P. minutus

increased in importance in 1980, reaching 26% and 8% o f the numerical

t o t a l , re s p e c tiv e ly . Conversely, A ca rtia copepodite numbers decreased

from approxim ately 6000/m^ in 1979 to 1000/m^ in 1980.

Species d iv e r s ity , in terms o f the number o f species p resent, was

lower fo r the summer-fall copepod community. A c a rtia tonsa dominated

the sum mer-fall assemblage, accounting fo r 60-90% o f the copepod to ta l ,

w ith a peak abundance o f >30,000 in d iv id u a ls /m ^ in Ju ly . The annual

maximum copepod abundance was observed in Ju ly , co in c id in g w ith the A.

tonsa peak. A ca rtia copepodites, Pseudodi aptomus coronatus, and

Labidocera aestiva were also present during the summer months, but in

r e la t iv e ly low numbers.

A c a rtia tonsa was the on ly copepod species to occur in 100% o f the

c o lle c t io n s . Qithona sp ., £_. coronatus, P_. m inutus, and Parvocalanus

c ra s s iro s tr is (= Paracalanus c r a s s iro s t r is ) each occurred in 10 o f the

14 sampling months. Paracalanus sp ., Corycaeus sp. and Centropaqes

typ icu s were ra re species, co lle c te d on ly during one month each.

35

Chaetognatha. Chaetognaths were the second most d iverse

ho lop lankton ic group sampled; abundance and species composition varied

seasona lly . This taxon was absent from c o lle c tio n s March through Ju ly

1979 w ith the exception o f the Zostera s ta tio n in A p r il (<0.1/m ^).

The summer-fall chaetognath assemblage was comprised o f S a g itta tenu is

(95%), S a g itta e n f la ta and low numbers o f S a g itta h is p id a . D ensities

o f 22/m^ and 36/m^ were observed in September (Zostera) and October

(Sand), re s p e c tiv e ly . A s in g le species was present in the 1980 w in te r

c o lle c t io n s . Saqi t t a elegans was recorded in February and March

reaching a peak abundance o f 15/m^. Chaetognaths never accounted fo r

more than 0.5% o f the zooplankton numerical t o ta l .

Meroplankton

Polychaeta. Polychaete larvae con tribu ted in high numbers to the

zooplankton assemblage during the t ra n s it io n period spring to summer

(F igure 8) . This taxon comprised between 15 and 38% o f the zooplankton

to ta l c o n s is te n tly A p r il through June at a l l th ree s ta tio n s . Maximum

d e n s itie s o f > 10^ in d iv id u a ls /m ^ were observed in A p r il 1979. Low

numbers (<70/m^) o f polychaete larvae were c h a ra c te r is t ic o f the

sum mer-fall c o lle c t io n s . S ta t is t ic a l ana lys is demonstrated th a t no

s ig n if ic a n t d iffe re n ce ex is ted between s ta tio n s in mean la rv a l

polychaete abundance over the 14-month pe riod .

M ollusca. Gastropod larvae were co lle c te d June through August

1979 and in A p r il 1980. Maximum abundances were observed in June

(450/m^, Zostera) and Ju ly (860/m^, Sand), representing between

36

Figure 8 Mean monthly abundance (log [(number per m^) + 1] ) o fto ta l polychaete larvae by s ta t io n , March 1979 - A p r il 1980. (R = Ruppia, Z = Zostera, S * Sand)

INI

CO

CON

oooa>

TT

cC

CO

coINI

0>N-0>

CON

CO

COM£T

"05"M

CO73"

CDUla:Z>CD

IO O in O IO o in

ro ro ro cJ — — o

[ I+ (£ uj/ x )] 6o|3VAdV“l 313VH0A10d i ° eoimpunqv

^

37

2-15% o f the zooplankton to ta l in these months. Pelecypod larvae were

present June through September 1979 and A p r il 1980. Abundance values

were less than 150/m3 except during August when la rv a l pelecypod

d e n s ity ranged from 600/m3 (Ruppia, Zostera) to 1400/m3 (Sand). At

no time did th is group account fo r more than 10% o f the to ta l

zooplankton standing s tock. A s in g le la rv a l cephalopod, L o lliq u n cu lu s

b rev is was co lle c te d in August at the Sand s ta t io n .

C ir r ip e d ia . Barnacle la rvae , both nauplius and cyp ris stages,

were present every month sampled. This taxon was an im portant

c o n s titu e n t o f the zooplankton community, A p r il through June, reaching

d e n s itie s > 300/m3 at a l l s ta tio n s (F igure 9 ). This time period

co inc ides w ith the t ra n s it io n between the w in te r-sp r in g and summer-fall

holoplankton assemblages. Barnacle larvae ranked th ird in numerical

abundance in A p r i l , c o n s t itu t in g 8% o f the zooplankton to ta l in 1979

and 16-20% in 1980. In May and June, c ir r ip e d e larvae represented

between 16 and 39% o f the numerical t o ta l , ranking among the three

numerical dominants at a l l s ta tio n s (Table 4 ). Low abundances (<50

in d iv id u a l/m 3) were c h a ra c te r is t ic o f c o lle c tio n s September through

February. S ta t is t ic a l ana lys is demonstrated th a t no s ig n if ic a n t

d iffe re n c e in mean barnacle larvae abundance exis ted between s ta tio n s

over the 14-month pe riod .

Decapoda. Decapod larvae co n s titu te d the most d iverse group o f

a l l the zooplankton taxa sampled during th is study. A to ta l o f 22

species was id e n t i f ie d , most o f which occurred s o le ly in summer

c o lle c t io n s June through August. Zoeal stages accounted fo r 99% o f the

decapod la rva e ; small numbers o f megalopae were also encountered.

38

Figure 9 Mean monthly abundance (log [(number per m^) + 1 ]) o fto ta l barnacle larvae by s ta t io n , March 1979 - A p r il 1980. (R = Ruppia, Z = Zostera, S = Sand)

<

o o O o o oo iq o iq q iqro csi CM — —

.P E___isl

_ L L

fsl

, N 1 C

CONce

CON

1 CE

I CO

r k

1 CO1 M

1 ce

1 CO1 NL CE

1 CONcr

1 CO1 N

I CE

1 CO1 N

CE

O00a>

CO

< o>

o>UJa:o

[I+ (2 UJ/X)] 6o|3VAHV1 310VNdVa P 9DUDpunqv

^

39

Decapod abundance was bimodal over an annual cycle (F igure 10).

D ensities g rea te r than 100 in d iv id u a ls /m ^ were observed in March o f

both years and in June and Ju ly 1979. Low numbers (<10/m^) were

recorded fo r seven of the 14 months sampled (A p r il 1979, 1980;

September 1979 - January 1980). S pa tia l v a r ia b i l i t y in decapod

abundance was high during the months o f peak abundance. However, the

d iffe re n c e in abundance between s ta tio n s was not s ig n if ic a n t over the

14-month period based on s ta t is t ic a l ana lys is using the Wilcoxon te s t .

The w in te r-s p r in g decapod assemblage (December through A p r i l)

consisted almost e n t ire ly (99%) o f zoeal Crangon septemspinosa. Low

numbers o f C a llianassa sp. ( - sp. A in S and ife r, 1972) and Pagurus

longicarpus occurred sp o ra d ic a lly in these c o lle c t io n s .

The number o f species co lle c te d per month increased s ix - fo ld from

March (n=3) to August (n=20). Palaemonetes sp. and £ . septemspinosa

predominated during the tra n s it io n -p e r io d (May and June) from spring to

summer. Uca sp ., £_. long ica rpus , P inn ixa chaetopterana, Palaemonetes

sp. , Neopanope texana, Sesarma re ticu lu m and Upogebia a f f in is comprised

approxim ately 85% o f the summer decapod assemblage (Ju ly and August).

In a d d it io n , C a llin e c te s sap idus, Emerita ta lp o id a , L ib in i a sp .,

Naushonia crangonoides, Ogyrides sp ., Pagurus p o l l ic a r is , Panopeus

h e rb s ti i , P inn ixa sayana, Pinnotheres maculatus, and Pinnotheres

ostreum were present during summer months in d e n s itie s o f less than

Figure 10. Mean monthly abundance (number per m^) o f to ta l decapod larvae and number o f species by s ta t io n , March 1979 - A p r il 1980. (R = Ruppia, Z = Zostera, S = Sand)

h O

SI

<

N

UTIS I

toNcc

toCM

OO to oto

coNCC

CONCC

CONCC

CONCC

M

IOCM

c=:

Tj

“STM

cojMCC

TT

CO

IO IO“ IoCM

( £ u ]/-O N )3 VAa\n oodvoia i v i o i do a iisnbo S3i03ds do on

FIGU

RE

10 19

79

I 19

80

41

o5 in d iv id u a ls /m ° each. The number o f species decreased ab ru p tly from

August (n=20) to September (n=4), co in c id in g w ith a decrease in to ta l

la rv a l decapod abundance.

In genera l, in d iv id u a l decapod species were d is tr ib u te d un ifo rm ly

between s ta tio n s . However, the abundance o f Palaemonetes sp. was

g e n e ra lly much g rea te r in Ruppia than in the Sand s ta t io n . For

example, in June Palaemonetes dens ity ranged from 142/m^ at Ruppia to

less than 1/m^ at the Sand s ta t io n . Palaemonetes sp. accounted fo r

g rea te r than 85% o f the decapod to ta l in Ruppia, May through June, and

less than 6% at the Sand s ta tio n during the same pe riod .

Phoronida. Phoronid larvae were present in Ju ly 1979 c o lle c t io n s .

Comprising less than 0.5% o f the zooplankton t o t a l , phoronid dens ity

ranged from 30/m^ at the vegetated s ta tio n s to 140/m^ at the Sand

s ta t io n .

P isces. Although f is h eggs and larvae were the second most

d ive rse m eroplanktonic taxa sampled, abundance values were the lowest.

However, nets w ith mouth opening less than 60 cm are not considered

e f fe c t iv e fo r q u a n tita t iv e sampling o f f is h larvae (Wiebe and-Hoi land ,

1968; Jacobs and Grant, 1978).

Fish eggs were present during seven o f the 14 months sampled but

occurred in numbers g rea te r than 1 individual/m^ only in la te spring

and e a rly summer (M ay-Ju ly). D ensities were c o n s is te n tly much lower,

by an order o f magnitude, at the Ruppia s ta tio n compared to Sand

42

(F igure 11A). Anchoa m itc h i11i and Sciaenidae eggs comprised 99% o f

the to ta l eggs sampled. Abundances g rea te r than 20 eggs/m^ were

observed at the Sand s ta tio n fo r A. m itch i H i (May and Ju ly ) and fo r

Sciaenidae (J u ly ) . Eggs o f Membras m a rtin ica and Gobiosoma sp. were

present in summer c o lle c tio n s w h ile B revoorti a tyrannus and

Scophthalmus aquosus eggs were co lle c te d in the w in te r . None o f these

fo u r species reached d e n s itie s g rea te r than 1 egg/m^ at any o f the

th ree s ta tio n s .

Fish larvae were present in every month sampled, occurring in

numbers g rea te r than 1 in d iv id u a l/m ^ from June through September

(F igure 11B). Gobiosoma sp. accounted fo r 80% o f the to ta l f is h larvae

during June 1979 w ith a maximum abundance o f 12/m^ (Z o s te ra ). Anchoa

m itch i H i dominated the la rv a l f is h assemblage Ju ly (68%) and August

(85%). Maximum d e n s itie s o f Anchoa larvae were observed in August (30

in d iv id u a ls /m ^) at Ruppia and Zostera. Also present in summer

c o lle c t io n s were low d e n s itie s o f Cynoscion re g a lis , Synqnathus fuscus ,

un id . Sciaenidae, M. m a rtin ic a , Hypsoblennius h e n tz i, M icroqobius

th a la s s in u s , T rinectes maculatus and P ep rilus a le p id o tu s .

Low abundances o f B_. t y r annus, Ammodytes sp ., Leiostomus

xanthurus, Pseudopleuronectes americanus, Tautoqa o n i t i s , M icro -

poqonias undu la tus, _S. aquosus, Anchoa hepsetus, Opisthonema oq1inum

and Paralichth.ys dentatus were observed in fa l l - w in te r c o lle c t io n s ,

November through A p r i l . In most cases, each species occurred during

on ly one month and in d e n s itie s less than 1 in d iv id u a l/m ^ .

43

Figure 11. Mean monthly abundance (number per m3) o f to ta l A.eggs B. Fish larvae by s ta t io n , March 1979 - A p r il (R = Ruppia, Z = Zostera, S = Sand)

Fish1980

35

i

S993 HSUm

3VAUVH HSU

(£uj/ 0N) 30NVQNn9V

44

Demersal Plankton

Polychaeta. Adu lt polychaetes were the second most d iverse

demersal taxon c o lle c te d ; a to ta l o f 12 species was id e n t i f ie d . In

gene ra l, low abundances (<2/m^) were c h a ra c te r is t ic o f c o lle c tio n s

October through March (F igure 12). Values >5/m^ were observed fo r

Ruppia and Zostera in A p r il (17/m^) and May (7/m^) and fo r Sand in

Ju ly (8/m^) and August (9/m ^). Results o f the Wilcoxon te s t ,

ind ica te d no s ig n if ic a n t d iffe re n ce in ad u lt polychaete abundance

between any s ta tio n p a irs (Ruppia-Zostera, Zostera-Sand, Ruppia-Sand).

Nereis succinea was the most common ad u lt po lychaete, accounting

fo r 36% o f the polychaete t o ta l . This species occurred March through

September 1979 w ith a maximum abundance o f 14/m^ in A p r i l . Scoloplos

sp. was present 8 o f 14 months sampled, also peaking in A p r il 1979

(4 /m ^). Paraonis fu lq e n s , Tharyx s e tiq e ra , Spionidae spp, Eteone

heteropoda, and T e rebe llidae spp, combined, accounted fo r 48% o f the

polychaete t o ta l . These species occurred sp o ra d ic a lly reaching maximum

abundance values between 2 - 8/m^.

The fo llo w in g species occurred in fre q u e n tly , never reaching

d e n s itie s > l/m ^: A u to ly tus sp ., C istena gou ld i i , Eteone la c te a ,

Glycera d ib ra n ch ia ta and Parahesione sp.

45

Q

Figure 12. Mean monthly abundance (number per nr3) o f to ta l adu lt polychaetes by s ta t io n , March 1979 - A p r il 1980. (R *Ruppia, Z * Zostera, S = Sand)

I6.0

H

I CO

L S

"T-o

“ T“ocsi

T -o o00

oCD

o oCM*

ST

N [

« c

I CN

__cr

toisl

“ ST

toN)cr

_£=Mcr

toNcr

to"Ncr

j d

CO

(sUJ/ ON) V13VHOA“IOd JPPV P GOimpunqv

FIGU

RE

12 19

79

1980

46

H arpactico ida . H arpactico id copepods were an im portant

c o n s titu e n t o f the zooplankton assemblage A p r il through June and in

November and December. This demersal taxon comprised 3-8% o f the

zooplankton to ta l in May 1979 and 1-5% in June, November, December 1979

and A p r il 1980. Abundance values >30/m^ were observed in A p r il o f

both years, May (134/m^), June, J u ly , and March 1980. Abundance

varied between s ta tio n s but no d iscernab le p a tte rn was apparent. This

taxon was considered as a group category and no attempt was made to

id e n t i fy in d iv id u a ls to species, except in the case o f A lteu tha

depressa. This r e la t iv e ly large ha rpac tico id (1.4mm) was present

November, December and A p r il through June in numbers < 15/m^. The

maximum abundance o f A. depressa was observed in May 1979 at the Sand

s ta tio n (130/m^).

Mysidacea. Mysids were the num erica lly dominant demersal taxon.

Abundance values were c o n s is te n tly >50/m^ August through February

(F igure 13). Mysids comprised between 5-9% o f the zooplankton to ta l in

September, 22-81% in November, 12-35% in December, and 3-15% in

January. Maximum d e n s itie s were observed in September 1979 at Ruppia

(494/rn^), Zostera (579/m^) and Sand (605/m^). Numbers >400/m^

were also c o lle c te d in August and February a t the Sand s ta t io n .

S ta t is t ic a l ana lys is ind ica ted no s ig n if ic a n t d iffe re n ce in mysid

abundance over the 14-month study period between any s ta tio n pa irs

(Ruppia-Zostera, Zostera- Sand, Ruppia-Sand).

47

Figure 13q

. Mean monthly abundance (number per n r) s ta t io n , March 1979 - A p r il 1980. Zostera, S = Sand)

o f to ta l mysids by (R = Ruppia, Z =

r -OOh-

ooCD

OOin

oo

ooro

OOcvl

03fsla:03INICE

Nl

N

|M

N

03N

03N

03NCC03m

03N

r~j~|

oo

CO

o00(J)

o>r -cr>

< 2Ljoc

2 |Lu

(e ^ J / 'O N ) V30VQ ISAIA I P © o u D p u n qy

48

A to ta l o f th ree species o f Mysidacea was id e n t i f ie d . Neomysis

americana accounted fo r 99% o f a l l the mysids c o lle c te d . This species

occurred in d e n s itie s >200/m^ fo r at leas t one s ta tio n in August,

September, and November through February. Abundance o f N. americana

varied between s ta t io n s , however no in te rs ta t io n pa tte rn was ev iden t.

Juveniles outnumbered adu lts August through October comprising 68-94%

o f the _N. americana t o ta l . Conversely adu lts outnumbered ju ve n ile s

November through February accounting fo r 66-92% o f the t o ta l .

Mysidopsis b iqe low i was the second most commonly occurring mysid.

This species was present Ju ly through September 1979 and in January

1980. Abundance o f M. b iqe low i was <2/m? throughout the sampling

period w ith the exception o f the Sand s ta tio n in August (19/nr*). A

th ir d species, Heteromysis formosa, occurred on ly in October at the

Sand s ta tio n (< l/m ^).

Cumacea. Another im portant demersal taxon, Cumacea, was present

in every month sampled and was represented by f iv e species. Abundance

o f to ta l cumaceans varied between months and between s ta tio n s (F igure

14); maximum den s ity values were observed in November (15/m^) and

December (20/m ^), both at the Ruppia s ta t io n . Abundances > 4/m^

were observed at the Ruppia s ta tio n 8 o f the 14 months sampled, Zostera

5 , and the Sand s ta tio n on ly once. S ta t is t ic a l ana lys is o f to ta l

cumacean abundance using the Wilcoxon te s t ind ica ted s ig n if ic a n t ly

h igher numbers at the Ruppia s ta tio n compared to Zostera and likew ise

h igher numbers at Zostera compared to Sand.

49

Figure 14 Mean monthly abundance (number per m3) o f to ta l cumaceans

S 3 1! 1979 - * r " I9 8 ° - <* ■ z ■

18"

CO

COINI

CO

CO

CO

CO

COINI

CO

CO CM (X) CO CM

(£Ui/ON) VBOVWnO P Goimpunqv

FIGUR

E 14

1979

19

80

50

During November and December 1979, cumaceans comprised between

4-6% o f the zooplankton to ta l at the Ruppia s ta tio n and 1% o f the to ta l

a t Zostera in December. At no other time did cumaceans account fo r

>0.5% o f the zooplankton numerical to ta l .

O xyu ros ty lis sm ith i was co lle c te d during a l l months sampled. In

general th is species occurred in low abundances (<2/m^), w ith the

exception o f September (5 /m ^), November (15/m^) and December

(4 /m ^). Cyclaspis varicans was present March through November,

dominating the cumacean assemblage, Ju ly through September and in March

1980 (>6/m ^)). Pseudoleptocuma minor was co lle c te d December through

June and dominated the cumaceans December through February. At the

Ruppia s ta tio n in December, £ . mi nor abundance was >15/m^, the

h ighest s in g le species de ns ity observed fo r any cumacean.

D ia s ty lis sp. was present during the spring months dominating the

cumaceans in A p r il (2 /m ^). Leucon americanus and Mancocuma

s t e l l i f e r a occurred in fre q u e n tly in numbers < l/m ^. In genera l,

abundance values were lowest at the Sand s ta tio n fo r each o f the f iv e

cumacean species.

Tanaidacea. An u n id e n tif ie d tanaid was present in c o lle c t io n s ,

May through September. The maximum abundance (1.5/m ^) was observed

in May at the Ruppia s ta t io n . Tanaids were co lle c te d at the Sand

s ta tio n on ly in September (<0.5 /m ^).

51

Isopoda. A to ta l o f fou r species o f the demersal taxon, Isopoda,

was co lle c te d during th is study. At the Ruppia s ta t io n , isopods were

present in every month sampled. However, th is group was absent from

Zostera c o lle c tio n s 3 months and from Sand c o lle c tio n s 7 months. Peak

abundance values fo r each s ta tio n were observed during Ju ly and

August: 12/m^ Ruppia, 12/m^ Zostera, and 5/m^ Sand. During a l l

o ther months, isopod abundance values were <5/m^. Based on

s ta t is t ic a l ana lys is (Wilcoxon te s t ) , no s ig n if ic a n t d iffe re n ce in

isopod abundance ex is ted between Ruppia and Zostera and likew ise

between Zostera and Sand. However isopod abundances were s ig n if ic a n t ly

lower at the Sand s ta tio n compared to Ruppia.

Edotea t r i lo b a and E richson e lla a ttenuata were the two dominant

isopod species c o lle c te d . Maximum d e n s itie s were 10/m^ (June) and

8/m^ (August) fo r E. t r i loba and E. a tte nua ta , re s p e c tiv e ly . Idotea

b a lth ic a occurred s p o ra d ic a lly October through A p r il in numbers less

than 1/m^. A p a ra s it ic cymothoid species was co lle c te d June through

November 1979 and A p r il 1980 in numbers <2/m^.

Amphipoda. Amphipoda was the most d iverse demersal taxon sampled;

eighteen gammarid and three c a p re ll id species were id e n t i f ie d .

Abundance o f to ta l amphipods varied between months and between s ta tio n s

(F igure 15); no d is t in c t seasonal pa tte rn was ev iden t. Amphipods

accounted fo r <1.0% o f the zooplankton t o ta l , eleven o f 14 months.

52

Figure 15. Mean monthly abundance (number per m^) o f to ta l amphipods and number o f species by s ta t io n , March 1979 - A p r il 1980. (R = Ruppia, Z = Zostera, S = Sand)

35 H

co r-R—*-

coj±C

coN

CONq:

CON l

CON l

£ 3 .

CO

NlCq:

Jt£LJ±

coN l

CON lcr

J£L_tL

N l

Jr±

CON lK c

I I I I I IO 10 O IO O 10ro CM CM — —

_r

~T~IO

co

no

(£ u i/0 N )VQOdlHdWV i© eouDpunqv S3IQ3dS dO ON

FIGU

RE

15 19

79

1980

53

During May 1979 and A p r il 1980, th is taxon comprised 1-2% o f the

zooplankton to ta l at both Ruppia and Zostera and 4% at Ruppia in

November 1979. At no time did amphipods account fo r >1.0% o f the to ta l

a t the Sand s ta t io n . D ensities o f <5/m3 were observed fo r the Sand

s ta t io n 12 o f 14 months, Zostera 6 o f 14, and the Ruppia 4 o f 14. The

peak amphipod abundance (45/m3) occurred at the Ruppia s ta tio n in

A p r il 1980.

Results o f the Wilcoxon te s t ind ica ted no s ig n if ic a n t d iffe re n ce

in amphipod abundance between the Ruppia and Zostera samples. However,

amphipod abundance was s ig n if ic a n t ly lower at the Sand s ta tio n compared

to e ith e r Zostera or Ruppia.

Monoculodes edwardsi, M icroprotopus ra n e y i» and Gammarus

mucronatus, combined, accounted fo r 78% o f a l l the amphipods c o lle c te d .

Monoculodes edwardsi was present in every month sampled; peak

abundances were observed at the Ruppia s ta tio n in December 1979

(18/m3) and A p r il 1980 (30/m3) . Most o f these specimens were small

young ju v e n ile s , probably re c e n tly hatched. M icroprotopus raneyi * was

present every month except February 1980, w ith a peak abundance o f

25/m° a t the Zostera s ta tio n in May 1979. Gammarus mucronatus was

c o lle c te d in a l l months except September 1979; young ju v e n ile s

outnumbered adu lts fo r th is species, a lso . Maximum d e n s itie s o f (3.

mucronatus reached l l /m 3 , in A p r il 1980 at the Zostera s ta t io n .

54

Other fre q u e n tly occuring amphipods included Cymadusa compta,

Corophium sp ., Ampithoe lonqimana, and Ampelisca sp. These species

demonstrated no seasona lity in occurrence, except fo r A. lonqimana

which was c o lle c te d on ly June through September. At no time did any o f

these species occur in numbers >10/m^.

The fo llo w in g species occurred s p o ra d ic a lly (u su a lly less than 4

o f 14 months) never reaching abundances > l/m ^: Batea c a th a rin e n s is ,

Bathyporeia sp. , Leptocheirus sp. , L is t r ie l la b a rn a rd i, M e lita

appendicu la ta , M. n i t id a , Parametopella c y p r is , Stenothoe m inuta,

Uncio la i r r o r a ta , and an u n id e n tif ie d haustorid species.

Of the th ree c a p re ll id species c o lle c te d , C apre lla penantis was

the most commonly occurring and most abundant. This species was

present March through October, w ith maximum d e n s itie s observed in Mayq q

(8/m°) and June (7 /m °). C apre lla e q u ilib ra and Paracapre lla tenu is

were each c o lle c te d in 5 o f 14 months sampled, gen e ra lly in numbers

<l/ra3 .

D ie l V a r ia b i l i t y .

Twelve day zooplankton samples were c o lle c te d , s ix in May 1979 and

s ix in August 1979. The day c o lle c tio n s were made during the high t id e

e ith e r immediately fo llo w in g or preceeding the monthly n ig h t sampling.

55

May n igh t c o lle c t io n s were characterized by r e la t iv e ly low numbers

o f to ta l organisms (900-1600/m^) compared to the other months sampled

during th is study. Meroplankton dominated the May n ig h t assemblage

(57-73%) fo llow ed by holoplankton (17-37%) and demersal plankton

(5-10%). In the May day c o lle c t io n s , the number o f to ta l organisms

(300-1100/m^) was lower than th a t observed fo r May n ig h t.

Meroplankton ranked f i r s t num erica lly during the day, comprising a

g rea te r percentage o f the to ta l than in the corresponding n igh t

samples. The demersal p lankton comprised on ly 1-3% o f the zooplankton

to ta l during the day in May.

In genera l, abundances o f copepods, polychaete la rva e , f is h eggs,

amphipods, and ha rpac tico ids were lower by an order o f magnitude in the

day c o lle c tio n s compared to the n igh t (Table 5 ). Three demersal groups

(a d u lt po lychaetes, cumaceans, and mysids) were present at n igh t in

r e la t iv e ly low numbers, <12/m^, but were absent from a l l day

c o lle c t io n s . Barnacle larvae comprised. 20-40% o f the zooplankton to ta l

a t n igh t and 40-80% during the day. However, th is is an a r t i f a c t o f

lower daytime holoplankton abundance, as barnacle larvae abundances

were s im ila r day vs. n ig h t.

The d is p a r ity between day and n ig h t abundance values varied among

s ta t io n s . At Ruppia and Zostera, the d iffe re n ce between day and n ig h t

d e n s itie s was much g rea te r than th a t observed fo r the Sand s ta t io n .

Daytime copepod and la rv a l polychaete abundances at the Sand s ta tio n

Table

5.

Day

versu

s nig

ht

taxon

ab

unda

nce

value

s (n

o. per

nr

) by

stat

ion,

1%

, 19

79.

58

I

§3 ^ s?>

*3f- LO C M i— IC O C O

CM CM tO <51- CO N/

C M C ''» C O C O C O C M o o o o

CO CO «—I coN/ o o o

S C M £ 1

LO »io *—}v v o o o

r*+Q

C M O ^ ^ H L Q t— i Q L O C M r ^ O O C O r - l g C g c d C O W C *

V

£IO

C M

V

scy»C O

fT3

■88~&

C_5

8>Js0)8cfo

C O

£8

JC=

£o

o _

fT3"Uoo•r»"

&

8>fe

■89r8

COCOS'

jtnl o ­

irs■gOL

ra•r~%JO‘EC_5

438

- c

r—o

Q_

I

I3*8“O•r *

j&

were , s im ila r to n ig h t Sand values and were an order of magnitude

g rea te r than the day values fo r Ruppia and Zostera.

August n ig h t c o lle c tio n s were characte rized by high numbers o f

to ta l organisms (9800-16800/m^) , dominated by copepods (86-92%).

Daytime August samples were also dominated by copepods (74-96%), how­

ever, the number o f to ta l organisms was lower gene ra lly by an order o f

magnitude than the corresponding n igh t c o lle c tio n s (Table 6 ).

Abundances o f pelecypod la rvae , copepods, f is h larvae and mysids were

much lower in the daytime than at n ig h t. Barnacle la rvae , gastropod

la rva e , decapod la rvae , and adu lt polychaetes exh ib ite d s im ila r

d e n s itie s between n ig h t and day c o lle c t io n s .

S im ila r to the May re s u lts , the d is p a r ity between day and n ig h t

abundances was g rea te r fo r the Ruppia and Zostera s ta tio n s in August.

A lso , day Sand copepod numbers were an order o f magnitude higher than

e ith e r Ruppia or Zostera day values. The species composition o f the

zooplankton assemblage did not vary between day and n igh t samples in

May or August 1979.

Zooplankton biomass (AFDW) was also g e n e ra lly lower in the daytime

than at n ig h t (Table 7 ). Day AFDW values were lower by an order o f

magnitude in May at Ruppia and Zostera and in August at Zostera

co in c id in g w ith lower daytime abundances o f to ta l zooplankton.

Likewise during May and August at Sand, the day AFDW value was

Table

6.

Day

versu

s nig

ht tax

on

abun

danc

e va

lues

(no.

per

irft by

stat

ion,

Au

gust,

19

79.

58

<cI— ICl.

O

cvj co q o>LO OO ^ CO COLO

a

if?LO

CO O ' LO 8

v

a to

v /

V/

o>

CO

cvj gj coQ cr>

o>

V /

8 8 " s Rl 00

v /

V

V

V

C O C O C Q ^ Q ^ T —l ^ - C ^ L O C \ i t ^ ^ 1— I ^ C O ^25 00

CVJ V

CVJ 00 O O O

CVJ

V / V V /

TCJ

■8

o

$I■8IrQ)Q _

8

l<ur —Id

CO

$s

8CD

8l*8f rIdo

$

I£$

J C

Ho

Q -

%■o•1“s=CO

<d■8Q .

8>r5

-Ctn

15%o

Q_ tOCD

=3O

rt3<d"8&(/>

TOTA

L 186

0 13

369

744

9856

9404

16

761

59

Table 7. Day versus n ig h t zooplankton ash-free dry weight values (mg/nrr) by s ta t io n , May and August 1979.

Month Ruppia Zostera Sand

May Day 55.7 21.5 51.7

N ight 397.5 132.4 118.6

August Day 379.8 14.9 104.6

N ight 121.3 163.9 263.5

60

approxim ately h a lf the n ig h t va lue , also s im ila r to the d ie l trend in

to ta l zooplankton numbers at th is s ta t io n . In c o n tra s t, zooplankton

biomass was higher during the day a t the Ruppia s ta tio n in August

compared to the n ig h t biomass. Tota l zooplankton abundance, however,

was lower by an order o f magnitude in these day samples.

DISCUSSION

Community S easona lity

Previous stud ies in Middle A t la n t ic embayments (Cowles, 1930;

Sage and Herman, 1972; A llan e t a l . , 1976; Jacobs, 1978; Maurer e t a l .

1978; and Grant and Olney, 1979) have described several general zoo­

plankton community c h a ra c te r is t ic s :

1) a lte rn a tio n o f two d is t in c t semi-annual assemblages;

2) peak periods o f zooplankton abundance h e av ily dominated by copepods, in p a r t ic u la r the congeneric p a ir A ca rtia c la u s i - A _ tonsa;

3) occurrence o f both estuarine and coasta l species;

4) h igher d iv e rs ity and species richness in the summer-fall assemblage; and

5) occasional high abundance o f m eroplanktonic organisms.

The data presented in th is study gene ra lly concurred w ith previous

c h a ra c te riza tio n s o f es tuarine zooplankton. In a d d it io n , several

community aspects unique to shallow-water seagrass systems were

observed.

Two d is t in c t zooplankton communities were id e n t i f ie d , a w in te r-

spring assemblage peaking in March and a summer-fall assemblage

peaking in August. Holoplankton, p r im a r ily calanoid copepods,

accounted fo r 70-90% o f the w in te r-sp rin g (January-March) and 75-95% o f

the sum mer-fall ( Ju ly-O ctober) c o lle c t io n s . C h a ra c te r is tic dominant

zooplankton species fo r each assemblage are presented in Table 8. The

61

62

Table 8. C h a ra c te r is tic zooplankton species from the two semi-annual assemblages: w in te r-s p r in g and sum m er-fa ll.

Taxon W inter-S pring Summer-Fa11

COPEPODA

CLADOCERA

CHAET06NATHA

DECAPOD LARVAE

A c a rtia c laus i

FISH LARVAE

CUMACEA

ISOPODA

AMPHIPODA

Centropages hamatus Temora lo n q ico rn is

Evadne nordmanni

S a g itta eleqans

Cranqon septemspinosa

B revoo rtia tyrannus Leiostomus xanthurus

O xyu ros ty lis sm ith i Pseudoleptocuma minor

Idotea b a lth ic a

A ca rtia tonsa Labidocera aestiva

Podon polyphemoides Evadne te rq e s tin a

S a g itta tenu is

Palaemonetes sp.Uca spp.P inn ixa spp.Xanthid spp.

Anchoa m itc h i11i Gobiosoma sp.

Cyclaspis varicans

Edotea t r i lo b a

Monoculodes edwardsi M icroprotopus raneyi

63

sum mer-fall community contained a g rea te r number o f to ta l species and

more in d iv id u a ls per m than the w in te r-sp rin g community.

To ta l zooplankton abundance was lower by an order o f magnitude

during the t ra n s it io n months, (A p ril-Ju n e and November-December)

between the two seasonal communities. C h a ra c te r is tic species from both

assemblages were present. Holoplankton g en e ra lly comprised less than

50% o f the numerical to ta l during the t ra n s it io n months. Meroplankton,

in p a r t ic u la r barnacle and polychaete la rvae , dominated (57-73%) the

zooplankton in May and June. During November and December to ta l

numbers o f holoplankton and meroplankton were at an annual low;

demersal taxa comprised from 13-93% o f the zooplankton to ta l at th is

t im e .

Zooplankton Biomass

Ash-free dry weight estim ates o f zooplankton biomass flu c tu a te d

e r r a t ic a l ly between successive months, e s p e c ia lly at the Ruppia and

Zostera s ta t io n s . These changes do not c o rre la te w ith increases or

decreases in the to ta l number of zooplankters. Analyses o f the

taxonomic samples in d ica te th a t in many cases the temporal biomass

v a r ia b i l i t y may be a ttr ib u te d to f lu c tu a tio n s in the abundance o f a

s in g le taxon. Certa in taxa , e sp e c ia lly in the demersal ca tegory, are

characte rized by large-bodied robust organisms. These in d iv id u a ls

although com paratively ra re num e rica lly , may s ig n if ic a n t ly increase the

biomass. The September peak in biomass, fo r example, co incides w ith

the annual peak abundance o f Mysidacea. Likewise in January, although

64

the number o f to ta l zooplankters was com paratively low, high abundance

o f ctenophores and mysids resu lted in higher biomass (AFDW) values.

Results o f the taxonomic analyses are also usefu l in exp la in ing

the monthly s p a tia l v a r ia b i l i t y in biomass. For example, the

r e la t iv e ly g rea te r biomass observed at the Zostera s ta tio n in December

and the Sand s ta tio n in February re f le c ts higher abundance o f mysids at

these s ta tio n s .

Jacobs (1978), using a s im ila r net and mesh s ize , determined

zooplankton AFDW from double-ob lique tows taken during the day in the

open waters o f the Chesapeake Bay proper. The AFDW data co lle c te d in

the present study (29-783 mg/m^) were ge n e ra lly higher and more

va ria b le than those observed at Jacob's s ta tio n c lo ses t to Vaucluse

Shores (<1-247 mg/m^). Values >200 mg/m were observed in 10 o f

the 13 months fo r th is study compared to 4 o f 24 months sampled by

Jacobs. The d iffe re n ce s observed in zooplankton biomass between the

two studies are probably due to f lu c tu a tio n s in 1) large-bodied

demersal organisms which m igrate in to the water column predom inantly at

n igh t and 2) increased d e t r i ta l load. One o f the inherent problems

w ith using gross community biomass techniques is the in a b i l i t y to

separate d e tr itu s from liv in g m a te r ia l. V isual examination o f the

taxonomic samples ind ica ted q u a l ita t iv e ly g rea te r amounts o f n o n -liv in g

d e t r i t a l m atter in the shallower Ruppia and Zostera s ta tio n s .

Increased wave action associated w ith wind may resuspend seagrass and

S partina d e t r i ta l m atter in these shallow -water areas.

65

These re s u lts suggest th a t conventional gross community biomass

estim ates may not r e f le c t actual trends in s p a tia l or temporal

zooplankton d is t r ib u t io n w ith in shallow-water es tuarine systems.

D e tr itu s and tra n s ie n t demersal taxa may s ig n if ic a n t ly d is to r t

community biomass va lues.

Holoplankton

Of the three major taxonomic components comprising shallow -water

zooplankton communities, holoplankton exh ib ite d the leas t s p a tia l

v a r ia b i l i t y throughout th is study. Abundance and species composition

o f the num erica lly dominant ho lop lankton ic taxa, Copepoda, were

e s s e n t ia lly uniform between the three s ta tio n s . High dens ity

aggregations o f copepods, in d ic a t iv e o f swarming, were not observed at

any s ta tio n during the present study.

Seasonal trends in copepod community s tru c tu re c lo s e ly p a ra lle le d

those observed by Jacobs (1978) and Grant and Olney (1979; 1982) fo r

the lower Chesapeake Bay proper. There was, however, a major

discrepancy in the temporal d is t r ib u t io n o f A ca rtia tonsa observed in

the present study. Semi-annual congeneric species replacement (A.

tonsa - A. c la u s i) is a well-documented phenomenon in M id d le -A tla n tic

es tua ries (Conover, 1956; J e f f r ie s 1962, 1967; Sage and Herman, 1972;

Jacobs, 1978). According to Jacobs (1978), A. tonsa was present

year-round in the lower Chesapeake Bay, dominating the zooplankton

assemblage August through December. A ca rtia c la u s i f i r s t appeared in

November and dominated the zooplankton February through May. By June,

A. c la u s i was absent from the lower Bay.

66

The March copepod community in the Chesapeake Bay is gene ra lly

characte rized by a g rea te r abundance, usu a lly by one or two orders o f

magnitude, o f A. c la u s i compared to A. tonsa (Table 9 ). This was the

case in the present study fo r March 1979. However, in 1980 s im ila r

numbers o f the congeneric p a ir were observed. A ca rtia c la u s i was

present in numbers comparable to those observed fo r March in previous

years. In c o n tra s t, the 1980 A. tonsa abundance was an order o f

magnitude higher than th a t o f 1979. In a d d it io n , Centropages hamatus

and Pseudocalanus minutus comprised a r e la t iv e ly g rea te r numerical

percent (35% vs 5%) o f the 1980 copepod community. A s im ila r

phenomenon occurred in 1975 fo r the Delaware Bay. According to Maurer

e t a l . (1978), A. c la u s i abundance did not exceed th a t o f A. tonsa;

instead £ . hamatus and Temora lo n q ico rn is dominated the w in te r

assemblage.

I t appears from these data th a t the congeneric replacement o f A.

c la u s i - A. tonsa may be an annually va ria b le phenomenon in southern

Middle A t la n t ic es tua ries or at leas t i t may be s p a t ia l ly lim ite d to

c e rta in p o rtio n s o f these e s tu a rie s . In March 1980, s a l in i t y was

roughly 3 ppt h igher (17 vs 20 pp t) than in March 1979 at the study

s i te . The g rea te r abundances o f ty p ic a l w in te r coasta l species l ik e £ .

hamatus, m inutus, and T. lo n q ico rn is in 1980, suggests an in tru s io n

o f s a l t ie r coasta l waters along the eastern side o f the Bay. A ca rtia

tonsa is a year-round re s id en t o f both estua rine and coasta l waters in

the southern M id -A tla n tic B ig h t, w h ile A. c la u s i is apparently confined

to estuarine waters (G rant, 1977a, 1979; Van Engel and Tan, 1965).

67

Table 9. Average abundance (no. per m^) o f adu lt A ca rtia tonsa andA ca rtia c la u s i in March.

In v e s tig a to r Year No. o f samples A. c laus i A. tonsa

Jacobs March 1972 24 21,500 410

Jacobs March 1973 24 2,603 95

Grant and Olney* March 1978 20 4,714 670

present study March 1979 6 7,996 532

present study March 1980 6 3,063 3,808

*using 60 cm net (0:202 mm)

68

Autochthonous popula tions o f A. tonsa in the Chesapeake Bay may be

augmented by in tru s io n s o f coasta l water popu la tions , re s u lt in g in

h igher A. tonsa abundance as was observed in 1980 at the study s i te .

In the middle po rtions and along the western side o f the Bay in 1980,

normal congeneric replacement o f A. tonsa by A. c la u s i may have been

o ccu rrin g .

Chaetognath and cladoceran abundance and species composition were

also d is tr ib u te d evenly between s ta tio n s . A l l species co lle c te d in

th is study, th e ir seasonal d is t r ib u t io n and abundance have been

p re v io u s ly recorded in the lower Chesapeake Bay (Bryan, 1977; Grant,

1977b).

Two ho lop lankton ic taxa , hydromedusae and ctenophores, e xh ib ited

v a r ia b i l i t y in s p a tia l d is t r ib u t io n . Q u a lita t iv e ly h igher d e n s itie s o f

these organisms were observed at the Ruppia and Zostera s ta tio n s

compared to the Sand s ta t io n . Ctenophores and hydromedusae may be

concen tra ting or swarming v ia a c tive o r ie n ta t io n in the reduced cu rren t

v e lo c ity water associated w ith the seagrass systems (assuming they

de tec t c u rre n ts ). As a second p o s s ib i l i t y , the seagrass blades may act

as a sieve to pass ive ly concentrate large-bodied spherica l p a r t ic le s

such as hydromedusae and ctenophores w h ile a llow ing sm aller p a r t ic le s

(copepods, cladocerans, e tc . ) to pass unimpeded.

Meroplankton

Meroplankton varied s p a t ia l ly to a g rea te r exten t than ho lo­

p lankton , but in general no cons is ten t in te rs ta t io n trends were

apparent. Larval barnacle , polychaete and decapod abundances were

69

s t a t is t ic a l ly s im ila r between s ta tio n s over the fourteen month study

p e rio d . Only f is h eggs e xh ib ited a co n s is ten t pa tte rn in s p a tia l

d is t r ib u t io n . Fish egg abundance was gen e ra lly an order o f magnitude

higher at the Sand compared to the Ruppia s ta t io n . Since f is h eggs are

considered incapable o f independent movement, an ac tive or n o n -s ta tic

mechanism may be responsib le fo r th is observed d is t r ib u t io n . Increased

predation by fishe s associated w ith seagrass areas may re s u lt in

reduced concentra tion o f f is h eggs at the Ruppia s ta t io n . There are no

stomach content da ta , however, to te s t th is hypothesis.

According to Olney ( in press) the center of spawning in the lower

Chesapeake Bay fo r Anchoa and Sciaenidae, the two dominant egg types

co lle c te d in th is study, is the mid-channel open Bay waters. The time

requ ired fo r tra n s p o rt to shallow water seagrass areas may be longer

than the developmental time o f these eggs CAnchoa m itc h iH i f e r t i l i ­

za tion to hatching = 24 hours at 27°C; Kuntz 1914). Thus, the eggs may

hatch before they are transported in to the bed, re s u lt in g in low egg

abundances at the Ruppia s ta tio n (J . Olney VIMS, pers. comm.).

Meroplankton abundance also varied tem pora lly ; w e ll-d e fin e d

seasonal pulses were apparent fo r each taxonomic group. High

d e n s itie s o f barnacle larvae and polychaete larvae were co lle c te d A p r il

through June, comprising 30-70% o f the zooplankton t o ta l . In the

Delaware Bay, Maurer e t a l . (1978) noted occassional numerical

dominance by meroplankters at shallow water s ta tio n s . Jacobs (1978)

also noted high d e n s itie s o f barnacle larvae A p r il through June 1972

70

and 1973 in the lower Chesapeake Bay. Numerical dominance o f the

zooplankton community by selected meroplankton species co incides w ith

the t ra n s it io n period between the two seasonal holoplankton

assemblages.

Larval decapod abundance exh ib ited two peaks over an annual cyc le .

Species composition and seasona lity o f the zoeal assemblage were

s im ila r to previous Chesapeake Bay ch a ra c te riza tio n s (S a nd ife r, 1973;

Jacobs, 1978; Grant and Olney, 1979; 1982). The w in te r decapod

community was overwhelm ingly dominated by Crangon septemspinosa.

D iv e rs ity , in terms o f the number o f species c o lle c te d , was much higher

during the summer and abundances were more evenly d is tr ib u te d between

species than in w in te r c o lle c t io n s .

Absolute abundance estim ates and re la t iv e numerical percentages o f

se lected decapod species d if fe re d in the present study from those

p rev iou s ly described. Considering annual v a r ia b i l i t y , sampling gear

d iffe re n c e s , and the lim ite d area sampled in th is s tudy, these

abundance d iffe re n ce s are presumed minor.

G enera lly , the abundance o f in d iv id u a l decapod species was

independent o f the presence o f seagrass. Except fo r Palaemonetes sp .,

there was no evidence th a t spawning by decapod species^ was re s tr ic te d

to the vegetated areas. Zoeal d e n s itie s o f Palaemonetes were higher at

Ruppia compared to the Sand s ta t io n . Sandifer (1973) also found lower

Palaemonetes abundances in open bay than York R iver c o lle c t io n s .

Species o f Palaemonetes (£_.. pug io , P. v u lg a r is , and £ . in te rm ed ius) ,

71

commonly known as grass shrimps, predom inantly in h a b it beds of

submerged aquatic vegetation in es tua rine systems (W illia m s , 1965).

Demersal Plankton

Demersal plankton exh ib ite d the g rea test s p a tia l v a r ia b i l i t y o f

the major taxonomic groups analyzed in th is study. S ig n if ic a n t ly

h igher numbers o f s p e c if ic demersal groups, in p a r t ic u la r Amphipoda,

Cumacea, and Isopoda were observed at the Ruppia and Zostera s ta tio n s

in comparison to the Sand s ta t io n . This g rea te r dens ity at the

vegetated s ta tio n s may be a ttr ib u te d to 1) p ro x im ity to the seagrass

system, a source o f benth ic organisms or 2) a shallower water column at

Ruppia and Zostera.

A lld redge and King (1980) demonstrated th a t most v e r t ic a l ly

m ig ra ting benth ic organisms r is e only 1-2 m o f f the bottom. Sampling

a t a f ix e d depth o f 1 m from the surface may cause d i f fe r e n t ia l capture

o f demersal p lank te rs between shallow and deep (>2 m) water s ta tio n s .

I do not fe e l , however, th a t the v a r ia b i l i t y in demersal abundance

observed in th is study is s o le ly an a r t i f a c t o f sampling depth.

Seagrass systems are considered an im portant source o f food, and

p ro te c tio n fo r numerous benth ic in ve rte b ra te species (den Hartog, 1977;

Heck and Wetstone, 1977; McRoy, 1977). Faunal d iffe rences between

vegetated and non-vegetated h a b ita ts have been well-documented (Santos

and Simon, 1974; O rth , 1973; Thayer e t a l . , 1975). In genera l, the

number o f species and dens ity o f ep ifaunal and in fauna l organisms are *

considerab ly lower in non-vegetated h a b ita ts . The physica l com plexity

o f seagrass increases s tru c tu ra l heterogeneity re s u lt in g in g rea te r

72

d iv e rs ity and abundance o f fauna in vegetated areas (O rth , 1977; Heck

and O rth , 1980).

The dens ity o f macrophytic cover may fu r th e r regu la te species

composition and abundance. Heck and Wetstone (1977) speculated th a t

the increased species richness observed in seagrass meadows is a

fu n c tio n o f grass blade dens ity which increases food a v a i la b i l i t y ,

l iv in g space, and p ro te c tio n from p redators. Thus, abundance of

macrobenthic organisms (N/m2) and species d iv e rs ity are d ir e c t ly

re la te d to mean macrophytic biomass (S toner, 1980).

Based on these s tu d ie s , a g rea te r abundance o f re s id en t benthic

organisms can be expected in areas o f submerged aquatic vege ta tion . In

the present s tudy, demersal p lankton was more abundant and comprised a

g rea te r percentage o f the to ta l zooplankton dens ity at vegetated

s ta tio n s in comparison to a non-vegetated s ta tio n and to previous

Chesapeake Bay zooplankton c h a ra c te r iz a tio n s . Demersal taxa are,

th e re fo re , im portant components o f the zooplankton community in shallow

shallow -w ater seagrass systems, more so than in adjacent non-vegetated

areas.

The tro p h ic importance of benthic inve rteb ra tes to d iu rna l

bottom -feeding f is h predators is w e ll known (Carr and Adams, 1973;

S tickney e t a l . , 1975; Sheridan, 1978). However, recent stud ies have

i l lu s t r a te d the impact benthic species, which move up in to the water

column at n ig h t, have upon the tro p h ic s tru c tu re o f nocturnal

p e la g ic -fe ed in g fish e s (Robertson and Howard, 1978; Hobson and Chess,

1978). A study conducted in the nearshore waters o f f C a lifo rn ia

73

(Hobson and Chess, 1976) co rre la te d d ie l changes in zooplankton

composition w ith food hab its o f various f is h p reda to rs . D iurnal

p lank tivo rous fish es consume predom inantly ho lop lankton ic organisms

( i . e . copepods and c ladocerans), w h ile demersal organisms comprise a

large p o rtio n o f the d ie t o f nocturnal p lank tivo rous f is h e s .

In Chesapeake Bay seagrass systems, there are at leas t two

nocturna l p e lag ic -fe e d in g f is h species which may b e n e fit from the

increased prey inpu t o f d ie l-m ig ra tin g demersal taxa: Membras

m a rtin ic a , the rough s ilv e rs id e and ju v e n ile B a ird ie lla chrysoura, the

s i lv e r perch. Concurrent w ith the time period o f th is study, the food

hab its of ju v e n ile s i lv e r perch in seagrass meadows were inves tiga ted

at the Vaucluse Shores study s ite (Brooks et a l . , 1981). U nfo rtuna te ly

no stomach data were co lle c te d fo r M. m a rtin ica during th is pe riod .

Several species co lle c te d at n igh t in the zooplankton samples also

occurred as prey items in stomachs o f ju v e n ile B_. chrysoura: Neomysis

americana, Gammarus mucronatus, C apre lla p e nan tis , Cymadusa compta,

Corophiurn sp ., and M icroprotopus raneyi (Brooks et a l . , 1981).

Juven ile s i lv e r perch ty p ic a l ly feed at n ig h t, in m id-water, consuming

prey d ir e c t ly in f ro n t o f them (Chao and Musick, 1977; H. Brooks, VIMS

pers. comm.). The mysid, N. americana, was an im portant food item by

number and by weight fo r s i lv e r perch 70-150 mm SL during September,

October, and November. This species was also the num erica lly dominant

demersal taxon co lle c te d at the Ruppia and Zostera s ta tio n s during

these months (200-500/m^). Gammarus mucronatus and C apre lla penantis

are ep ifauna l amphipods (McCain, 1968; B o u s fie ld , 1973) and may have

74

been consumed d ir e c t ly from th e ir h a b ita t on the seagrass blades.

However, M. ra n e y i, £ . compta, and Corophium sp. are tu b e -b u ild in g

in fauna l amphipods (B o u s fie ld , 1973). Since no evidence o f benthic

feeding (sand or tubes) was observed in the stomachs (Brooks, pers.

comm.), ju v e n ile s i lv e r perch are probably consuming these prey items

as they m igrate in to the water column at n ig h t. Thus, re s id en t

demersal zooplankters may represent an im portant energy source to

nocturna l mid-water fish e s in Chesapeake Bay seagrass systems.

Several hypotheses have been presented to exp la in the fu n c tio n a l

s ig n if ic a n c e o f d ie l m ig ra tion by benth ic in ve rte b ra te s . Movement in to

the water column subjects these demersal organisms to increased

p redator pressure by n o c tu rn a l, m id-water f is h e s ; thus, a counter­

balancing advantage fo r v e r t ic a l m ig ra tion must e x is t (Robertson and

Howard, 1978).

H is to r ic a l ly , the p lank ton ic presence o f many demersal taxa has

been co rre la te d w ith feeding hab its (Blegvad, 1922). Emery (1968)

speculated th a t many carnivorous benthic inve rteb ra tes such as some

species o f polychaetes, cumaceans and amphipods m igrate to forage on

holoplankton in the water column. Many omnivorous species o f

Mysidacea also feed n o c tu rn a lly on small zooplankton (Hobson and Chess,

1976; Cooper and Goldman, 1980). The mysid, Neomysis americana,

c o lle c te d in th is study was observed c o n s is te n tly in large numbers in

the water column. L i t t le in fo rm ation e x is ts on the feeding hab its o f

NL americana, however o ther species o f Neomysis are zooplanktivorous

75

(Murtaugh, 1981; S iegfred and Kopache, 1980). The consistency and

la rge numbers in which N. americana appeared in the water column at

n ig h t ind ica tes feeding as a probable fu n c tio n a l advantage o f v e r t ic a l

m ig ra tion in th is species.

Most o f the other demersal taxa co lle c te d in th is study, however,

are herb ivorous. For example, (a. mucronatus, M. ra n e y i, Ampelisca sp .,

A. longimona, E. t r i lo b a and £ . a ttennata feed p r im a r ily on e p ip h y tic

a lgae, benthic d r i f t algae or m icrob ia l f lo r a associated w ith d e t r i ta l

p a r t ic u la te m atter (M i l ls , 1967; Nelson, 1980; Zimmerman et a l . , 1979;

Smith et a l . , 1979; Orth and Boesch, 1979). M igra tion by these

species, thus, is probably unre lated to feeding behavior.

W illiam s and Bynum (1972) co rre la ted the m ig ra to ry behavior o f

many amphipod species w ith avoidance o f nocturnal predation by benthic

feeding fis h e s . Subsequent stud ies (Hobson and Chess, 1976; Robertson

and Howard, 1978) have re jec ted th is hypothesis on the grounds th a t

most benthic feeding occurs during d a y lig h t, s tim u la ted by v isua l cues.

In fa c t , the opposite case appears to e x is t , w ith increased predation

pressure in the m id-waters at n ig h t.

The v e r t ic a l m ig ra tion o f ce rta in benth ic inve rteb ra tes has been

linked to reproductive s tra te g y . Some polychaete species, fo r example,

synchronously swarm at the surface to spawn (C la rk , 1965; Evans, 1911).

In th is study most o f the adu lt polychaetes were co lle c te d in low

numbers. No monospecific swarms were observed; sexual epitokes were

ra re . The amphipod, Ampelisca sp ., an in fauna l tu b e -b u iId e r, enters

76

the water column p e r io d ic a lly to mate when sexua lly mature (M il ls ,

1967). Several o f the gammarid amphipod species co lle c te d fre q u e n tly

in th is study in c lud ing Ampelisca sp ., Cymadusa compta, Corophium sp .,

and Ampithoe lonqimana, are in fauna l or ep ifauna l tube -bu iIde rs

(B o u s fie ld , 1973). These organisms may increase the p ro b a b ility o f

su cce ss fu lly encountering a mate by leaving th e ir tubes and a c t iv e ly

searching.

Another possib le exp lanation of demersal v e r t ic a l m ig ra tion

invo lves ecdysis. The cumacean, D ia s ty lis ra th ke i was observed by

Anger and V a lentin (1976) to m igrate in to the water column at n igh t

on ly during ecdysis in the B a lt ic Sea. Specimens o f D ia s ty lis sp. and

Cyclaspis varicans captured in the present study were undergoing

ecdysis as evidenced by p a r t ia l ly discarded molts attached to the

p leon. No other demersal p lank te rs showed signs o f m o ltin g .

Another advantage o f v e r t ic a l m ig ra tion may be the h o rizon ta l

d isp e rsa l o f benthic in ve rteb ra tes v ia water cu rre n ts . A lldredge and

King (1980) concluded th a t benth ic organisms en te ring the water column,

i f on ly fo r a b r ie f period of tim e, may be dispersed over short

h o rizo n ta l d istances p oss ib ly re lo c a tin g them to more favorab le

h a b ita ts . A s t r ik in g fe a tu re o f the present study was the large number

(45/m^) o f ju v e n ile amphipods, p a r t ic u la r ly (3. mucronatus and M.

edwardsi c o lle c te d p e la g ic a lly . Grant and Olney (1979; 1982) observed

h igher d e n s itie s o f (a. mucronatus, M. raneyi and Corophium sp. in

77

surface waters compared to subsurface waters o f the Chesapeake Bay

proper. These data suggest th a t v e r t ic a l m ig ra tion may be an im portant

mechanism fo r h o rizo n ta l d ispe rsa l o f selected amphipod species. This

behavior may promote rap id re co lo n iz a tio n o f d is tu rbed s ite s and reduce

com petition between ju ve n ile s and adu lts (Robertson and Howard, 1978;

A lldredge and K ing, 1980).

The temporal d is t r ib u t io n o f demersal taxa co lle c te d in th is study

was h ig h ly v a r ia b le . No cons is ten t seasonal trends were apparent fo r

many o f the groups and in te rannua l v a r ia tio n was high fo r a l l groups.

Demersal taxa e x h ib it sp e c ie s -sp e c ific d ie l m ig ra tion p a tte rn s , i . e . ,

when they enter the water column and how long they s tay. Using

a r t i f i c a l l y darkened emergence tra p s , A lldredge and King (1980)

demonstrated th a t absence o f l ig h t is a major cue s tim u la tin g

m ig ra tio n . In some species, p a r t ic u la r ly amphipods (M acquart-M oulin,

1976), the tim ing o f m ig ra tion may also be a ffec ted by c irca d ia n

rhythms. In a d d it io n , fa c to rs such as age, sex, ecdysis and spawning

co n d itio n may regu la te an in d iv id u a l's m ig ra tion pa tte rn on a

p a r t ic u la r n ig h t (A lld redge and K ing, 1980). Thus species composition

and abundance o f demersal plankton may vary from dusk to dawn and

between successive n ig h ts .

In th is study a l l n igh t sampling was conducted at high t id e ,

regard less o f moon phase or actual tim e. The temporal d is t r ib u t io n o f

demersal zooplankton abundance observed in th is study may be a re s u lt

78

o f v a r ia b i l i t y in l ig h t le v e l, moon phase or in te rn a l m o tiva tion

fa c to rs ra th e r than actual temporal changes in numbers o f organisms.

The high degree o f temporal v a r ia b i l i t y must be kept in mind when

comparing demersal zooplankton abundance between studies or between

s ta tio n s o f the same study when sampled days or even several hours

a part.

D ie! A v a i la b i l i t y

Abundance o f o b lig a te and fa c u lta t iv e zooplankton also varied

tem pora lly on a d ie ! bas is . D ie l changes in the v e r t ic a l d is t r ib u t io n

o f zooplankton have been well-documented, e sp e c ia lly in oceanic

environments (Bary, 1967; Longhurst, 1976, Zaret and S u ffe rn , 1976;

Robertson and Howard, 1978). The general pa tte rn o f m igra tion

e xh ib ite d by most species is upward at dusk and downward at dawn,

re s u lt in g in higher d e n s itie s near the surface o f the water column at

n ig h t.

In th is study, to ta l zooplankton abundance was g reater in n igh t

c o lle c t io n s , u su a lly by an order of magnitude, compared to day

c o lle c t io n s . In most cases, demersal taxa were absent during d a y lig h t

or present in very low numbers compared to n igh t le v e ls . The d ie l

v a r ia b i l i t y o f demersal zooplankton and i t s fu n c tio n a l s ig n ifica n ce

have been presented p rev io u s ly in th is d iscuss ion .

D ie l changes in the abundance o f o b lig a te zooplankton varied among

taxa . Larvae o f f is h , polychaete and pelecypod species exh ib ited the

ty p ic a l trend o f higher abundances in n igh t c o lle c t io n s . Uniform

79

abundances o f barnacle , gastropod and decapod larvae were observed

between day and n ig h t.

The most apparent d ie l change was observed fo r copepod abundance.

At the Ruppia and Zostera s ta t io n s , copepod numbers decreased by an

order o f magnitude during d a y lig h t. However, copepod abundance at the

Sand s ta tio n was s im ila r or on ly s l ig h t ly g reater at n ig h t compared to

day. Copepods undergoing v e r t ic a l m ig ra tion downward at dawn may

p oss ib ly be moving in to water deeper than the water flo o d in g the

seagrass meadow at high t id e . Thus fewer copepods would a c u ta lly enter

the seagrass bed during the day. Another possib le explanation

invo lves increased predation in areas o f submerged aquatic vegetation

by s ig h t-fe e d in g p la n k tiv o re s . Many species of p o s tla rva l and ju v e n ile

f is h , fo r example, are more abundant at the Ruppia and Zostera s ta tio n s

(Brooks, et al 1981). Grazing on copepods by these predators may

re s u lt in lower copepod abundances at the Ruppia and Zostera s ta tio n s

compared to Sand.

The number o f d ie l comparisons analyzed in th is study was

inadequate to evaluate the v a l id i t y o f th is trend in copepod abundance.

In fa c t , other zooplankton data co lle c te d during the day at the same

s ta tio n s in con juction w ith another study con trad ic ted the d ie l changes

observed above. Using the same pushnet apparatus, zooplankton was

co lle c te d during the day at Ruppia, Zostera, and Sand approxim ately

every fo u rth day during A p r il 1980 (Meyer, unpubl. d a ta ). Daytime

80

copepod abundance values were s im ila r between vegetated and unvegetated

samples (Meyer, unpublished d a ta ), A p r il is the month o f peak

p o s tla rv a l spo t, Leiostomus xanthurus abundance in lower Chesapeake Bay

seagrass beds (M erriner and B oeh le rt, 1979); th is species feeds

p r im a r ily on copepods as a postla rvae (K je lson e t a l , 1975). I f

p redation were the cause o f the observed s p a tia l v a r ia b i l i t y in

copepod abundance, one would expect much lower copepod d e n s itie s a t the

vegetated s ta tio n s during A p r il 1980. However, th is trend was not

observed (Meyer, unpubl. da ta ).

A d d itio n a l research on d ie l changes in the d is t r ib u t io n o f

holoplankton in shallow-water areas is necessary. Such research is

d es irab le in view o f recent specu la tion on the importance o f such areas

as nursery grounds fo r a v a r ie ty o f f is h species (Reid, 1954; Carr and

Adams, 1976; Adams, 1976).

Summary

Composition, abundance, seasona lity and community s tru c tu re o f the

ho lop lank ton ic and m eroplanktonic assemblages co lle c ted in lower

Chesapeake Bay seagrass systems c lo se ly resemble deeper, open water

zooplankton populations of the Bay proper. In c o n tra s t, demersal

p lankton was more abundant than in the Bay, comprising a g rea te r pe r­

centage o f the zooplankton to ta l at s ta tio n s associated w ith submerged

aquatic vegetation (SAV).

81

The source o f o b lig a te plankton fo r SAV beds appears to be

adjacent deeper, non-vegetated areas. Zooplankton is transported in

and out o f the seagrass meadow v ia flo o d in g and ebbing waters. Thus,

there is a p o te n tia l energy gain to the SAV ecosystem in terms of

exogeneous zooplankton imported on a flood t id e . The importance of

th is inpu t to the o v e ra ll energy flow in h ig h ly productive ecosystems

such as seagrass beds is poorly known. Regardless o f what percentage

zooplankton con trib u te s to the o ve ra ll system p roduction , a number o f

adu lt p lanktivo rous fish es and inve rteb ra tes re ly on p lankte rs as prey

item s. Seagrass systems are u t i l iz e d fo r refuge by a v a r ie ty o f f is h

species and l i f e h is to ry stages. Inputs o f zooplankton to seagrass

beds on a t id a lly - re p le n is h e d basis may represent a s ig n if ic a n t source

o f n u t r i t io n to such p lan k tivo re s seeking refuge in an otherwise

d e tr ita l-b a s e d ecosystem.

Resident members o f the benthic substra te represent a second

source o f organisms to zooplankton communities in seagrass systems.

These fa c u lta t iv e forms or demersal plankton v e r t ic a l ly m igrate in to

the water column p e r io d ic a lly , e s p e c ia lly at n ig h t. Demersal taxa p lay

an im portant tro p h ic ro le during the day fo r numerous d iu rn a l b e n th ic -

feeding f is h e s , however, as they m igrate up in to the water column they

become an im portant food supply fo r nocturnal p e lag ic -feed ing p la n k t i­

vores. During n ig h t ly ebb t id e s , demersal plankton may be exported

from th e ir res iden t bed in high d e n s it ie s , thus representing an energy

loss from the res iden t SAV ecosystem.

CONCLUSIONS

1. One hundred tw e n ty -fo u r species were id e n t if ie d from 93

c o lle c tio n s over the 14 month study pe riod , March 1979 - A p r il 1980.

Two d is t in c t semi-annual assemblages were apparent, a w in te r-s p rin g

assemblage peaking in March and a summer-fa11 assemblage peaking in

August. Peak periods o f zooplankton abundance were dominated (70-90%)

by copepods, in p a r t ic u la r the congeneric p a ir A ca rtia c la u s i - A.

tonsa . During the t ra n s it io n a l months between the two seasonal

communities, zooplankton abundance was lower by 1-2 * orders o f

magnitude. At these tim es, meroplankton and demersal taxa comprised a

g rea te r percentage o f the zooplankton to ta l .

2. Ash-free dry weight estim ates o f zooplankton biomass ranged from

29-783 mg/nr and f lu c tu a te d e r r a t ic a l ly between successive months,

e s p e c ia lly at the vegetated s ta tio n s . Conventional gross community

biomass estimates may not r e f le c t actual trends in s p a tia l or temporal

zooplankton d is t r ib u t io n w ith in shallow-water seagrass systems.

D e tr itu s and tra n s ie n t demersal taxa may s ig n if ic a n t ly d is to r t biomass

values in these areas.

82

83

3. D ie l changes in zooplankton abundance varied among taxa.

Copepods, most demersal taxa , and larvae o f f is h , polychaete and

pelecypod species were more abundant at n igh t compared to day

c o lle c t io n s , u sua lly by 1-2 orders o f magnitude. Barnacle, gastropod

and decapod larvae abundances were s im ila r between d ie l pe riods.

4. Holoplankton exh ib ite d the leas t s p a tia l v a r ia b i l i t y throughout

th is study. Abundance and species composition o f Copepoda, Cladocera,

and Chaetognatha were e s s e n tia lly uniform between s ta tio n s . Mero-

p lankton varied s p a t ia l ly to a g rea te r ex ten t than ho lop lankton, but in

general no cons is ten t in te rs ta t io n trends were apparent. Abundances of

la rv a l barnacles, polychaetes, and decapods were s t a t is t ic a l ly s im ila r

between s ta tio n s . However, f is h egg abundance was an order o f

magnitude lower at the Ruppia compared to the Sand s ta t io n .

5. Composition, abundance, seasona lity and community s tru c tu re o f the

ho lop lankton ic and meroplanktonic assemblages sampled in th is study

c lo s e ly resembled ch a ra c te riza tio n s of deeper, open water zooplankton

popu la tions in the lower Chesapeake Bay proper. G enera lly , the

abundance o f in d iv id u a l species was independent o f the presence of

seagrass.

84

6 . Demersal p lankton was more abundant, comprising a g reater

percentage o f the zooplankton to ta l at s ta tio n s associated w ith sub­

merged aquatic vegetation compared to the nonvegetated s ta tio n and the

Bay proper. S ig n if ic a n t ly h igher numbers o f s p e c if ic demersal groups,

in p a r t ic u la r Anphipoda, Cumacea, and Isopoda were observed at the

Ruppia and Zostera s ta tio n s . The g rea te r dens ity o f demersal plankton

a t the vegetated s ta tio n s may be a ttr ib u te d to 1) p rox im ity to the

seagrass system, a source o f benthic organisms, and 2) a shallower

water column at the Ruppia and Zostera s ta tio n s .

7. As re s id en t demersal organisms v e r t ic a l ly m igrate in to the water

column at n ig h t they become a p o te n t ia l ly im portant energy source to

nocturna l m id-water fish e s in Chesapeake Bay seagrass systems.

8 . W ithin shallow -water seagrass meadows there are two sources o f

p la n k to n ic organisms. Most o b lig a te p lankte rs o r ig in a te in deeper Bay

waters and are transported in to the system v ia flo o d in g waters. Facul­

ta t iv e p lankton , however, are re s id en t members o f the seagrass meadow

b e n th ic -su b s tra te and enter the water column v ia p e rio d ic v e r t ic a l

m ig ra tio n .

APPENDIX

Primary references

AMPHIPODA

CHAETOGNATHA

CLADOCERA

COPEPODA

CUMACEA

DECAPODA

fo r id e n t if ic a t io n o f zooplanktonic taxa

Bousfie ld (1973)

Fox and Bynum (1975)

McCain (1968)

Grant (1963)

D ella Croce (1974)

Murphy and Cohen (1978)

Owre and Foyo (1967)

Rose (1933)

Sars (1903)

Wilson (1937a)

Wilson (1937b)

W atling (1979)

Sandifer (1972)

85

86

ISOPODA

MYSIDACEA

PISCES

POLYCHAETA

MISCELLANEOUS

Schultz (1969)

T a tte rs a ll (1951)

U.S. Fish and W ild l i fe Service (1978)

Day (1973)

Fauchauld (1977)

Gardiner (1976)

P e tt i bone (1963)

Calder (1971)

Gosner (1971)

LITERATURE CITED

Adams, S.M. 1976. Feeding ecology o f eelgrass communities. Trans.Amer. F ish. Soc. 105:514-519.

A lla n , J .D ., T.G. Kinsey, and M.C. James. 1976. Abundances andproduction o f copepods in the Rhode R iver Subestuary o fChesapeake Bay. Chesapeake S c i. 17:86-92.

A lld redge , A.L. and J.M. King. 1977. D is tr ib u t io n , abundance andsubstra te preferences o f demersal re e f zooplankton at Lizard Is land Lagoon, Great B a rr ie r Reef. Mar. B io l. 41:317-333.

A lld redge , A.L. and J.M. K ing. 1980. E ffec ts o f moonlight on thev e r t ic a l m ig ra tion pa tte rns o f demersal zooplankton. J. exp. mar. B io l. E co l. 44:133-156.

Anger, K. and C. V a le n tin . 1976. In s itu studies on the d iu rna la c t iv i t y pa tte rn o f D ia s ty lis ra th ke i and i t s importance fo r the hyperbenthos. Helgolander w iss. Meeresunters. 28:138-144.

Bary, B. 1967. D ie l v e r t ic a l m igrations o f underwater s c a tte r in g , mostly in Saanich In le t , B r it is h Columbia. Deep-Sea Res.14:35-50.

Blegvad, H. 1922. On the b io logy o f some Danish gammarids and mysids. Rept. Danish B io l. S ta t. No. 28:1-103.

B o u s fie ld , E.L. 1973. Shallow-water gammaridean Amphipoda o f New England. C ornell Univ. Press, Ithaca . 312 p.

B radford , J.M. 1976. P a r t ia l re v is io n o f the A ca rtia subgenus A ca rtiu ra (Copepoda: C a la n o id a :A ca rtiid a e ). N .Z.J. mar. fre sh .Res. 10:159-202.

Brooks, H .A., J.V . M e rrine r, C.E. Meyer, J.E. Olney, G.W. B oeh le rt,J .V . Lascara, A.D. Estes, and T.A. Munroe. 1981. Higher Level Consumer In te ra c tio n s . Ch. 4 in D ra ft Report on Contract R805974 w ith Environmental P ro tec tion Agency. Va. In s t, o f Marine Science.

87

88

Bryan, B.B. 1977. The ecology o f the marine Cladocera o f lower Chesapeake Bay. Ph.D. d is s e r ta t io n . U n iv e rs ity o f V irg in ia , C h a r lo t te s v il le , V irg in ia . 105 p.

B u r re l l , V.G. J r . , W.A. Van Engel and S.G. Hummel. 1974. A new devicefo r subsampling plankton samples. J. Cons. in t . Exp lo r . Mer.35:364-366.

Calder, D.R. 1971. Hydroids and Hydromedusae o f Southern Chesapeake Bay. Special Papers in Marine Science Number 1. Va. In s t, o f Marine Science, 125 p.

C arr, W.E. and C.A. Adams. 1973. Food habits o f ju v e n ile marine fish e s occupying seagrass beds in the estuarine zone near C rysta l R ive r, F la . Trans. Am. F ish . Soc. 102:511-539.

Chao, L.N. and J.A. Musick. 1977. L ife h is to ry , feeding h a b its , and fu n c tio n a l morphology o f ju v e n ile sciaenid fishe s in the YorkR ive r, Estuary, Va. F ish . B u ll. 75:657-702.

C la rk , R.B. 1965. Endrocrinology and reproduction in polychaetes.pp. 211-255. H. Barnes (e d .) , Ann. Rev. Oceanogr. Mar. B io l . , A llen and Unwin, London.

Conover, R.J. 1956. Oceanography o f Long Island Sound, 1952-1954. V I. B iology o f A ca rtia c la u s i and A. tonsa. B u ll . Bingham Oceanogr. C o ll. 15:156-233.

Cooper, S.D. and C.R. Goldman. 1980. Opossum shrimp (Mysis r e l ic ta ) p redation on zooplankton. Can. J. F ish. Aquat. S c i. 37:909-919.

Cowles, R.P. 1930. A b io lo g ic a l study o f the o ffsho re waters of Chesapeake Bay. B u ll. U.S. Bur. F ish . 46:277-381.

Day, J.H. 1973. New polychaeta from Beaufort w ith a key to a l l species recorded from North C aro lina . NOAA Tech. Rep. NMFS C irc . 375, 140 p.

D e lla Croce, N. 1974. Cladocera. Fiches d 'id e n t. du zooplankton. Sheet 143. Conseil In te rn a tio n a l pour 1'e x p lo ra tio n de la mer, 4 p.

den Hartog, C. 1977. S tru c tu re , func tion and c la s s if ic a t io n in seagrass communities, pp. 89-122. j_n C.P. McRoy and C. H e lf fe r ic h (e d s .) , Seagrass Ecosystems. Marcel Dekker, In c ., New York.

Emery, A.R. 1968. P re lim ina ry observations on cora l re e f p lankton. Lim nol. Oceanogr. 13:293-303.

Evans, S.M, 1971. Behavior in polychaetes. Q. Rev. B io l. 46:379-405.

89

Fauchald, K. 1977, The Polychaete worms: d e f in it io n s and keys to theOrders, Fam ilies and Genera. Natural H is to ry Museum o f Los Angeles County. Science Series 28, 188 p.

Fenwick, G. 1978. Plankton swarms and th e ir predators at the Snares Is lands . N. Z. J. mar. fre s h . Res. 12:223-224.

Fox, R.S. and K.H. Bynum. 1975. Anphipod crustaceans o f NorthC aro lina Estuarine w aters. Chesapeake S c i. 16:223-237.

G ardiner, S.L. 1976. E rrant Polychaete Annelids from North C aro lina . J. E lisha M itc h e ll S c i. Soc. 91:77-220.

Glynn, P.W. 1973. Ecology o f a Caribbean cora l re e f. The P o rite sr e e f - f la t b io tope: Part 2. Plankton community w ith evidence fo rd e p le tio n . Mar. B io l. 22:1-21.

Gosner, K.L. 1971. Guide to in d e n t if ic a t io n o f marine and estuarinein ve rte b ra te s , Cape Hatteras to the Bay o f Fundy. W ile y - In te r - science, New York. 693 pp.

G rant, G.C. 1963. In ve s tig a tio n s o f inner Continental She lf waterso f f lower Chesapeake Bay. Part IV. D escrip tions o f the Chaetognata and a key to th e ir id e n t i f ic a t io n . Chesapeake Sci.4:107-119.

Grant, G.C. 1977a. Middle A t la n t ic B ight zooplankton: seasonal bongoand neuston c o lle c tio n s along a tran se c t o f f southern New Jersey. V irg in ia In s t . Mar. S c i. , Spec. Rep. Appl. Mar. Sci. and Ocean Eng. No. 173, 138 pp.

Grant, G.C. 1977b. Seasonal d is t r ib u t io n and abundance o f the Chaetognatha in the lower Chesapeake Bay. Est. Coast. Mar. S c i. 5:809-824.

Grant, G.C. 1979. Middle A t la n t ic B ight zooplankton: second yearre s u lts and a d iscussion o f the two-year BLM-VIMS survey. V irg in ia In s t. Mar. S c i. , Spec. Rep. Appl. Mar. Sci. and Ocean Eng. No. 192, 236 pp.

G rant, G.C. and J.E . Olney. 1979. Lower Bay zooplankton m onitoring program: An In tro d u c tio n to the program and re s u lts o f thei n i t i a l survey o f March 1978. Special S c ie n t if ic Report Number 93. Va. In s t , o f Marine Science, 92 p.

Grant, G. and J. Olney. 1982. Lower Bay zooplankton m onitoring program: Results o f August 1978. Special S c ie n t if ic Report ( inprep) Va. In s t, o f Marine Science.

Hamner, W.H. and J.H. C arle ton . 1979. Copepod swarms: a ttr ib u te s andro le in co ra l re e f ecosystems. Limnol. Oceanogr. 24:1-14.

90

Heck, K .L . ,J r . and R.J. O rth. 1980. Seagrass H ab ita ts : The ro les ofh a b ita t com plex ity , com petition and predation in s tru c tu r in g associated f is h and m o tile m acroinvertebrate assemblages. pp. 449-464. jjn V.S. Kennedy (e d .) , Estuarine Perspectives, Academic Press, New York.

Heck, K .L . ,J r . and G.S. Wetstone. 1977. H ab ita t com plexity and in ve rte b ra te species richness and abundance in tro p ic a l seagrass meadows. J. Biogeogr. 4:135-142.

Hobson, E.S. and J.R. Chess. 1976. Trophic in te ra c tio n s among fish esand zooplankters near shore at Santa C a ta lina Is la n d , C a lifo rn ia .F ishery B u ll. 74:567-598.

Hobson, E.S. and J.R. Chess. 1978. Trophic re la tio n s h ip s among fishesand plankton in the lagoon at Enewetak A to l l , M arshall Is lands. F ishery B u ll. 76:133-153.

Hobson, E.S. and J.R. Chess. 1979. Zooplankters th a t emerge from thelagoon f lo o r at n ig h t at Kure and Midway A to l ls , HA. Fishery B u ll. 77:275-279.

H ollander, M. and D.A. Wolfe. 1973. Non-parametric s ta t is t ic a l methods. John W iley and Sons, In c ., New York. 503 p.

Jacobs, F. 1978. Zooplankton d is t r ib u t io n , biomass, biochemical composition and seasonal community s tru c tu re in lower Chesapeake Bay. Ph.D. d is s e r ta t io n . U n ive rs ity o f V irg in ia ,C h a r lo t te s v il le , V irg in ia . 105 p.

Jacobs, F. and G.C. Grant. 1978. Guidelines fo r zooplankton sampling in q u a n tita tiv e baseline and m onitoring programs. Special S c ie n t if ic Report Number 83. Va. In s t, o f Marine Science, 52 p.

J e f fe r ie s , H.P. 1962. Succession o f two A ca rtia species in e s tua rie s . Lim nol. Oceanogr. 7:354-364.

J e ffe r ie s , H.P. 1967. S a tu ra tion o f estuarine zooplankton by congeneric associa tes. pp. 500-508. J ji G.H. Lauff (e d .) ,

* Estuaries Publ. No. 83, AAAS, Washington, D.C.

Johannes, R .E ., S.L. Coles, and H.T. Kuenzel. 1970. The ro le o f zooplankton in the n u tr i t io n of some S c le ra c tin ia n co ra ls . Lim nol. Oceanogr. 15:579-586.

K iku ch i, T. 1961. An eco log ica l study on animal community o f Zostera b e lt in Tomioka Bay, Amakusa, Kyushu ( I ) Fish Fauna. Rec. Oceanogr. Works Jap. 5:211-223.

K je lson , M.A. and G.N. Johnson. 1976. Further observations of the feeding ecology o f post la rv a l p in f is h , Lagodon rhomboides and spo t, Leiostomus xanthurus. Fishery B u ll. 74:423-432.

91

K je lson , M .A., D.S. Peters, G.W. Thayer, and G.N. Johnson. 1975. General feeding ecology of p o s tla rva l fish es in the Newport R iver estuary . F ish. B u ll. 7 3 (1 ):137-144.

K r ie te , W .H .,Jr. and J.G. Loesch. 1980. Design and re la t iv e e ff ic ie n c y o f a bow-mounted pushnet fo r sampling ju v e n ile pe lag ic f is h e s . Trans. Amer. F ish . Soc. 109:649-652. *

Kuntz, A. 1914. The embryology and la rv a l development o f B a ird ie lla chrysura and Anchovia m i t c h i l l i . U.S. Bur. F ish. B u ll. 33:1—19.

Longhurst, A.R. 1976. V e rt ic a l m ig ra tio n , pp. 116-137. j j i D.H. Cushing and J .J . Walsh (e d s .) , The Ecology o f the Seas, B lackw ell.

M acquart-M oulin, C. 1976. Rythmes d 'a c t iv i t e 1 p e rs is ta n ts chez les Peracarides du plankton nocturne de Mediterranee (Amphipodes, Isopodes). Mar. Behav. P hys io l. 4 :1-15.

Maurer, D., L. W atling , R. Lambert, and A. Pembroke. 1978. Seasonal f lu c tu a t io n o f zooplankton populations in lower Delaware Bay. H ydrob io log ia . 61:149-160.

McCain, J.C. 1968. The C apre llidae (Crustacea: Amphipoda) o f the Western North A t la n t ic . Smithsonian In s t itu t io n B u lle t in 278. U.S.. National Museum, 197 p.

McRoy, C.P. 1977. Seagrass ecosystems: Research recommendations o f the In te rn a tio n a l Seagrass Workshop. In te r . Decade Ocean. Exp lo r .62 p.

McW illiam, P .S ., P.F. Sale, and D.T. Anderson. 1981. Seasonal changes in res iden t zooplankton sampled by emergence traps in One Tree Lagoon, Great B a rr ie r Reef. J. exp. mar. B io l. Ecol. 52:185-203.

M e rrin e r, J.V . and G.W. B oeh le rt. 1979. Higher leve l consumer in te ra c t io n s . Annual Report to EPA Chesapeake Bay Program. Grant No. R805974. Va. In s t, o f Marine Science.

M i l le r , J.M. 1973. A q u a n tita t iv e pushnet system fo r transec t stud ies o f la rv a l f is h and macrozooplankton. Limnol. Oceanogr. 18:175-178.

M il ls , E.L. 1967. The b io logy o f an ampeliscid amphipod crustacean s ib lin g species p a ir . F ish. Res. Bd Can. 24:305-355.

Murphy, J.A. and R.E. Cohen. 1978. A guide to the development stages o f common co a s ta l, Georges Bank and G ulf o f Maine, Copepods. N ational Marine F isheries Serv ice , Woods Hole Laboratory, Woods Hole, MA. Laboratory Reference No. 78-53.

92

Murtaugh, P.A. 1981. S e lec tive predation by Neomysis mercedis in Lake Washington. Lim nol. Oceanogr. 26:445-453.

Nelson, W.G. 1980. The b io logy o f eelgrass (Zostera marina L . ) amphipods. Crustaceana 39:59-89.

Olney, J.E. In press. Eggs and e a rly larvae o f the bay anchovy,Anchoa m i t c h iH i , and the weakfish, Cynoscion re g a lis , in lower Chesapeake Bay w ith notes on associated ich thyop lankton. Estuaries 6 (1 ).

O rth , R.J. 1973. Benthic infauna o f ee lgrass, Zostera m arina, beds. Chesapeake S c i. 14:258-269.

O rth , R.J. 1977. The importance o f sediment s t a b i l i t y in seagrasscommunities, pp. 281-300. j j i B.C. Coull (e d .) , Ecology o f Marine Benthos, U. South C aro lina Press, Columbia.

O rth , R.J. and D.F. Boesch. 1979. In te ra c tio n s in vo lv in g res iden t consumers. Annual Report to EPA Chesapeake Bay Program. GrantNumber R805974. Va. In s t, o f Marine Science.

Owre, H.B. and M. Foyo. 1967. Copepods o f the F lo rid a C urrent.In s t i tu te o f Marine Science, U n ive rs ity o f Miami, Miami, F lo rid a . C on trib . No. 748, 137 p.

P e ttibone , M.H. 1963. Marine polychaete worms o f the New Englandregion I . Aphrod itidae through Trochochaetidae. B u ll. U.S. N a t'l Mus. 227:1-346.

P o rte r, J.W. and K.G. P o rte r. 1977. Q ua n tita tive sampling o f demersal p lankton m igra ting from d if fe re n t cora l re e f substra tes . Limnol. Oceanogr. 22:553-556.

Reid, G .K., J r . 1954. An eco log ica l study o f the Gulf o f Mexicof is h e s , in the v ic in i t y o f Cedar Key, F lo r id a . B u ll. Mar. Sci.G ulf Caribb. 4 :1-94.

Robertson, A . I . and R.K. Howard. 1978. D ie l tro p h ic in te ra c tio n sbetween v e r t ic a lly -m ig ra t in g zooplankton and th e ir f is h predators in an eelgrass community. Mar. B io l. 48:207-213.

Rose, M. 1933. Copepodes pelagigues. Faune de France. 26:1-374.

Sage, L.E. and S.S. Herman. 1972. Zooplankton o f the Sandy Hook Bay Area, N.J. Chesapeake S ci. 13:29-39.

93

Sale, P .F ., P.S. McWilliam, and D.T. Anderson. 1976. Composition o f the nea r-ree f zooplankton at Heron Reef, Great B a rr ie r Reef. Mar. B io l. 34:59-66.

S and ife r, P.A. 1972. Morphology and ecology o f Chesapeake Bay decapod crustacean la rvae. Ph.D. d is s e r ta t io n . U n ive rs ity o f V irg in ia , C h a r lo t te s v il le , V irg in ia . 532 p.

S and ife r, P.A. 1973. D is tr ib u t io n and abundance o f decapod crustacean larvae in the York R iver Estuary and adjacent lower Chesapeake Bay, V irg in ia , 1968-1969. Chesapeake S c i. 14:235-257.

Santos, S.L. and J .L . Simon. 1974. D is tr ib u t io n and abundance o f the polychaetous annelids in a south F lo rid a estuary . B u ll. Mar. Sci. 24:669-689.

Sars, G.O. 1903. An account o f the Crustacea o f Norway. Vol. 4. Calanoida. The Bergen Museum, Bergen. 171 p.

S chu ltz , G.A. 1969. Marine Isopod Crustaceans. Wm. C. Brown Company P ub lishers , Dubuque. 359 p.

Sheridan, P. 1978. Trophic re la tio n s h ip s o f dominant fish es in the Apalach io la Bay System (F lo r id a ) . Ph.D. d is s e r ta t io n . F lo rid a State U n iv e rs ity , Tallahassee, F lo r id a . 216 p.

S ieg e l, S. 1956. Nonparametric s ta t is t ic s fo r the Behavorial Sciences. McGraw H i l l , New York. 312 p.

S ie g fr ie d , C.A. and M.E. Kopache. 1980. Feeding o f Neomysis mercedis (Holmes). B io l. B u ll. 159:193-205.

Smith, D .F ., N.C. B u lle id , R. Campbell, H.W. H igg ins, F. Rowe, D.J. T ra n te r, and H. T ran te r. 1979. Marine food-web ana lys is : Anexperimental study o f demersal zooplankton using is o to p ic a lly la b e lle d prey species. Mar. B io l. 54:49-59.

S tickney, R.R., G.L. T ay lo r, and D.B. White. 1975. Food hab its of f iv e species o f young southeastern United States estuarine Sciaenidae. Chesapeake S c i. 16:104-114.

S toner, A.W. 1980. The ro le o f seagrass biomass in the o rgan iza tiono f benthic macrofaunal assemblages. B u ll. Mar. S c i. 30:537-551.

T a t te r s a ll , W.M. 1951. A Review o f the Mysidacea o f the United StatesNational Museum. B u ll. U.S. N a t 'l Mus. 201:1-292.

94

Thayer, G.W., D.E. Hoss, M.A. K je lson , W.F. H e tt le r , and M.W. LaCroix. 1974. Biomass o f zooplankton in the Newport R iver Estuary and the in fluence o f p o s tla rv a l f is h e s . Chesapeake S ci. 15:9-16.

Thayer, G.W., S.M. Adams, and M.W. LaCroix. 1975. S tru c tu ra l and fu n c tio n a l aspects o f a re ce n tly estab lished Zostera marina community, pp. 518-540. j[n L.E. Cronin (e d .) , Estuarine Research, Academic Press, New York.

U.S. Fish and W ild l i fe Service. 1978. Development o f Fishes o f the M id -A tla n tic B igh t. An A tlas o f Egg, Larval and Juvenile Stages. FWS/OBS-78/12. Part I -V I.

Van Engel, W.A. and E. Tan. 1965. In ve s tig a tio n s o f Inner Continental She lf Waters o f f Lower Chesapeake Bay. Part VI. The Copepods. Chesapeake Science 6(3):183-189.

W atling , L. 1979. Marine F lora and Fauna o f the Northeastern UnitedS ta tes. Crustacea: Cumacea. NOAA Tech. Rep. NMFS C irc . 423,18 p.

Wayne, C.J. 1974. E ffe c t o f a r t i f i c i a l seagrass on wave energy andnearshore sand tra n s p o rt. Trans. G ulf Coast Assoc. Geol. Sci. 24:279-282.

W etzel, R .L ., P.A. Penhale, and K.L. Webb. 1981. P lant Community s tru c tu re and physica l-chem ica l regimes at the Vaucluse Shores Study S ite . Ch. 2 Section A. D ra ft Report on Contract R805974 w ith Environmental P ro tection Agency. Va. In s t, o f Marine Science.

Wiebe, P.H. and W.R. Holland. 1968. Plankton patchiness: e ffe c ts onrepeated net tows. Limnol. Oceanogr. 13:315-320.

W illia m s , A.B. 1965. Marine decapod crustaceans o f the C aro linas. F ishery B u ll. 65:1-298.

W illiam s, A.B. and K.H. Bynum. 1972. A ten-year study o f meroplankton in North C aro lina e s tua rie s : amphipods. Chesapeake Sci.13:175-192.

W illiam s, R .B., M.B. Murdoch, and L.K. Thomas. 1968. Standing crop and importance o f zooplankton in a systemn of shallow es tu a rie s . Chesapeake S c i. 9:42-51.

W ilson, C.B. 1932a. The copepods o f the Woods Hole reg ion . United States National Museum B u ll. 158. 635 p.

W ilson, C.B. 1932b. The copepod crustaceans o f Chesapeake Bay. Smithsonian In s t i tu t io n No. 2915 Proceedings o f the United States National Museum Vol. 80 A r t . 15, 54 p.

95

Z are t, T.M. and J.S. S u ffe rn . 1976. V e rtic a l m ig ra tion inzooplankton, a predator avoidance mechanism. Lim nol. Oceanogr. 21:804-813.

Zimmerman, R., R. Gibson, and J. H arring ton. 1979. Herbivory andd e t r i t iv o r y among gammaridean amphipods from a F lo rid a seagrass community. Mar. B io l. 54:41-47.

VITA

Cathy E lizabeth Meyer

Born in Pensacola, F lo rid a 31 January, 1956. Graduated F ir s t

C o lon ia l High School, V irg in ia Beach, V irg in ia in June 1974. Received

a Bachelor o f Science degree in Marine B io logy, F lo rid a In s t i tu te o f

Technology, June 1978. Entered College o f W illiam and Mary as a

m aster's student in School o f Marine Science, September 1978.

Employed as Research A ss is ta n t, McNeese State U n ive rs ity (Lake

Charles, Louisiana) on a Department o f Energy b rine disposal m onitoring

program, February 1981.

96