Demartini and Roberts 1990 Effects of Kelp on Fish Density

832019 Demartini and Roberts 1990 Effects of Kelp on Fish Density

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BULLETIN OF MARINE SCIENCE 46(2) 287-3001990

EFFECTS OF GIANT KELP (MACROCYSTIS) ON

THE DENSITY AND ABUNDANCE OF FlSHES IN A

COBBLE-BOTTOM KELP FOREST

Edward E DeMartini and Dale A Roberts

ABSTRACT

The density of fishes was compared among regions with differing densities of giant kelp

(Macrocystis pyrifera) at San Onofre Kelp bed (SOK) off northern San Diego county Cali-

fornia during the fall periods of 1985 and 1986 Fish densities and the density of giant kelp

were estimated by divers on belt transects Bedwide (total) fish abundance was computed as

the product of fish density and area of the respective kelp density region summed over all

regions of differing kelp density Fish-kelp density relations were evaluated by ANCOVA

and fish abundances compared between fall seasons by t-test adjusted for unequal variances

Fish density was significantly related to the density of giant kelp for 18 of 30 life stages of

the 14 major species tested and in all 18 cases the relation was positive Kelp-by-year

interactions were significant for IS life stages of II species Year effects were apparent for

13 cases involving 8 species Bedwide fish density was twice as great during the second versus

first fall season Bedwide abundances of fish were 75 greater (numbers) and 100 greater

(biomass) during the second fall season when both the density and abundance of Macrocystis

at SOK was about half the respective value in fall 1985 Thus more fish were concentrated

within less kelp in the second year The implications of these observations for describing

fish-kelp relations are discussed

The large and fast-growing giant kelp Macrocystis pyrifera is a conspicuousfeature of shallow rocky reefs off of the western coast of North America (North1971a) Nearly 100 species of fish are known to inhabit forests of giant kelp off southern California (Feder et a1 1974) Kelp forest habitats have diverse func-

tions Macrocystis undoubtedly provides complex combinations of animal foodshelter and water-column extension of benthic habitat for fishes (Quast 1968a1968c Feder et aI 1974 Bray and Ebeling 1975 Hobson and Chess 1976Bernstein and Jung 1979 Coyer 1979 1984 Hobson et aI 1981 Ebeling and

Laur 1985 1988 Bodkin 1986 1988) Kelp beds are also thought to enhancethe productivity of organisms including fishes in part directly via herbivory(North 1971 b) but primarily through a detrital pathway to invertebrate grazers

that provide the major prey of many fishes (Foster and Schiel 1985)Despite this wealth of supposed positive effects the relationship between kelp

density and the density of fishes in kelp beds is poorly known Coyer (1979)observed two- to eight-fold declines in the densities of several canopy species of fishes following one-half to three-fourths reductions in Macrocystis densities atSanta Catalina Island off southern California Larson and DeMartini (1984) ob-served 38-63 lower fish densities in sparse Macrocystis (versus regions of dense

surface canopy) at San Onofre Kelp bed also in southern California in fall 1979In a study comparing fish densities in Macrocystis forests and structurally lesscomplex temporally unstable Nereocystis beds in central California Bodkin (1986)

found biomass densities of a dominant water-column fish to be gt50 lower in Nereocystis beds Experimental removal of Macrocystis from a I-ha area of rock reef adjacent to a similar control area in central California resulted in a 63decline in the standing stock of fishes (Bodkin 1988) Ebeling and Laur (1988)

observed 20 declines in total fish densities at Naples Reef off Santa Barbara

2 8 7



2 8 8 BULLETIN OF MARINE SCIENCE VOL 46 NO2 1990

most of which resulted from loss of kelp habitat due to storm damage and urchingrazmg

In this paper we relate the density of fishes to the density of giant kelp (Macrocys-

tis pyrifera) anchored on a low-relief cobble seabed One objective is to extendLarson and DeMartinis (1984) evaluation of fish-kelp relations at this kelp bedto include all post-recruit life stages of major fish species present during twosubsequent but consecutive fall seasons of observation A second objective is toestimate bedwide fish abundances during each period of study and to contrastpatterns of density and abundance for fish and for kelp

MATERIALS AND METHODS

Study Area - We conducted this study in San Onofre Kelp bed (SOK) a forest of giant kelp Macrocystis

pyrifera anchored on a low relief ( lt I-m high) cobble bottom offshore of San Onofre northern SanDiego County California (Larson and DeMartini 1984 fig I) Stations sampled were in the middle

and offshore regions of the kelp bed 2 to 3 km from shore in 12-18 m of water Average bottom

depth sampled was 145 m

Fish Sampling Methods-Methods described herein generally follow those of Larson and DeMartini

(1984) Fish densities were estimated in two ways depending on the vertical stratum being sampled

On and near bottom fish densities were estimated directly by divers visual counts Fishes were

counted on belt transects as transect lines were paid out on swims radiating from fixed station hubs

Transect bearings were selected randomly from within arcs of permissible kelp habitat In midwater

and just below the surface canopy we used Super-8 cine transects to record fish observations for

later tallying of fish (Ebeling et aI 1980a 1980b) Cinetransects were swum along random bearings

within permissible arcs but lines were not used Divers swam at relatively constant rates filming

continuously while panning across observed fish until the film cartridge was exhausted (about 3 min)

Six-bottom two-midwater and eight-canopy transects were sampled per survey (date) at a station

For all species except one fish were scored as one of three size-specific maturity stages (J = juvenile

S = subadult A = adult) on in situ diver counts and film tallies Juvenile kelp bass (Paralabrax

clathratus) were further classified into young-of-year (YOY) and older juveniles (OJ) Stages were

recognized based on estimated total length (TL) in inches and a defined size-maturity relation for the

species For fish that averaged 15 to 30 em (6 to 12 in) TL the error of divers estimates was -211 2

em (s I in) based on the results of practice surveys where divers estimated the lengths of preserved

fish tethered along transect lines (E DeMartini unpubI data)

Dimensions of transects were either fixed (bottom) or variable but estimable (midwater and surface)

All bottom transects were 3-m wide by I5-m high by 75-m long (225 m2 area 3375 m3 volume)

Fish counts on bottom transects were standardized to number 1000 m-3bull Dimensions of midwater

(76-m depth) and surface canopy (3I-m depth) transects depended on lateral underwater visibility

Film counts were standardized to a volume of 1000 m3 Filmed at a swimming speed of 25 mminthe 3-min cinetransects were about 75-m long Data were collected during daylight (0800-1600) when

average lateral underwater visibility was 25 m

We estimated densities for each maturity stage of 14 species selected on the basis of adequate

abundance and frequency of occurrence in samples Densities were integrated over the water column

by weighting for the thickness of each relevant sampling stratum Stratum thickness was determined

by boundaries that extended midway between sampling depths (surface canopy 53 m midwater 77

m bottom 15 m) Relevant strata differed among species depending on whether the species inhabited

the canopy bottom midwater or was cosmopolitan in its distribution (Appendix Table I)

The length frequency distributions of fishes were characterized on timed random searches that

complemented our transect swims All fish encountered during these searches were classified by species

and size-class (TL in inches) Totals of 1800 min and 1360 min were spent characterizing length

distributions in 1985 and 1986 respectively DeMartini et aI (1989) provide additional detailsData were collected at five stations during the normally clear-water period (October-December) of

1985 and 1986 Surface canopy midwater and bottom microhabitats were usually sampled during a

single day at each station All stations could not be sampled on the same day however A team of

the same four divers conducted from four to eight surveys at each ofthe five stations during each fall

period (Appendix Table I)

Station positions were chosen based on the density of giant kelp Two stations were located in

regions of highest existing Macrocystis density one station in sparse kelp and two stations in regions

of intermediate kelp density In fall 1985 the two stations in densest available kelp averaged 20-22

plants 100 m-2 and the intermediate stations averaged 8-10 plants 100 m-2bull In fall 1986 kelp



DEMARTINI AND ROBERTS KELP EFFECTS ON ASHES 289

densities at the same two top-range stations averaged 10 plants 100 m- and the two intermediate

stations averaged 2-4 plants 100 m- During both fall periods kelp density at the sparse-kelp stationaveraged lt1 plantmiddot 100 m-

Measuring Giant Kelp - We estimated the density of Macrocystis by counting all juvenile-adult plants(gt I-m tall) encountered within a 3-m wide path on the return swims of the bottom fish transectsDensities were standardized to number of plantsmiddot 100 m-

Density Data Analyses - We related kelp density to fish density using ANCOVA (PROC GLM SASInc 1985) Year (fall season) was evaluated as a class variable and kelp as a covariate in ANCOVA

A kelp-by-year interaction term was evaluated in initial program runs Each life stage ofthe 14 select

fish species was evaluated separately in this portion of the analysesThe raw fish density data had generally skewed distributions and variances were usually heteroge-

neous Therefore before analyses standardized fish density data were converted to the form log(x +c) where the proportionality constant c was the smallest possible nonzero weighted density per 1000

m3bull (This constant represented the equivalent of one fish present on one transect in one sampling

stratum the minimal value perturbed data the least while avoiding the undefined logarithm ofzero)

The value of c varied among species depending on which sampling strata were relevant for the speciesvalues ranged from 0046 (for cosmopolite and canopy-midwater species) to 0125 (canopy species)

to 0495 (bottom species) Transformed in this manner the fish density data were normally distributedwith homogeneous variances We used raw values to characterize the density of giant kelp (Preliminary

analyses indicated that neither transformation of Macrocystis counts nor use of curvilinear functions

of kelp improved R2 values) Appendix Table I lists the regional means and standard errors of thekelp density data and untransformed fish density data These data in station-specific form provide

the bases for the ANCOV AsAdditionally densities of all 14 fish species pooled were regressed on kelp densities during each fall

period This was done in order to illustrate temporal patterns of the general fish-kelp relationship

Biomass as well as number of fishes was evaluated because fish size distributions might have differed

among kelp density regions in which the numbers of fishes did not The data used in this exercise

included all water column strata and therefore were restricted to the subset of dates on which all strata

were quantitatively sampled at a station Densities were integrated throughout the water column andstandardized on an areal (1000 m) basis We estimated biomass density as the product of mean

stage-specific numerical density and body weight The body weight of each maturity stage was calculated

using length-frequency distributions and length-weight regressions (Quast 1986b E DeMartini un-pub data)

Analyzing Fish Abundance -Fish abundance was computed as the product of area and fish densityper unit area Fish density per unit area was calculated for each station on each sampling date as the

sum (over water-column strata) ofthe density per unit volume ofa stratum times the thickness ofthe

stratum The means and variances of stations were then calculated over all sampling dates Totalabundance throughout the SOK bed was calculated as the sum of the products of abundance means

for each region of kelp density times the area of the kelp density region For each station the variance

of abundance was estimated as the among-date variation of the date estimates The variance of

estimated bed wide abundance was calculated as a weighted sum of the variances for all regions of kelp density Two-tailed t-tests adjusted for Satterthwaites approximation because variances were

usually unequal (Bailey 1981 185) were used to compare estimates of abundance between fall periods

The degrees offreedom used in t-tests were identified for each fall period as the number of sampling

dates minus one at each station summed over all stations

REsULTS

Effects of Kelp Density -Macrocystis directly influenced fish density in 27 of 43cases tested and in all 27 ofthese cases the effect was positive (Table 1) Excludingthe 13 non-independent cases (for All stages and for pooled YOY and older

juvenile kelp bass) densities in 18 of 30 specieslife-stage categories were posi-tively related to giant kelp (Table 1) Fish densities were directly or indirectlyrelated to kelp density for one or more life stages of 11 of 14 species (Table 1)Kelp-by-year interactions were frequently important and contributed more thantwo-thirds of the effect averaged over all cases Macrocystis explained an average24 of the observed variation (partial R2 =024) in fish density for the 30 life-

stages and 14 species Values ranged to a maximum of 73 (for kelp perch Brachyistius frenatus) The densities of only three species (topsmelt Atherinops



290 BULLETIN OF MARINE SCIENCE VOL 46 NO2 1990

Table I Summary results of ANCOVAs testing for the effects of giant kelp year (fall season) and

kelp-by-year interaction on densities of select fishes at San Onofre Kelp bed during 1985 and 1986

Kelp effect indicated as positive (+) if significant (P lt 005) each year Kelp effect indicated asinconsistent if insignificant (ns P gt 005) in 1985 but significant (either + or -) in 1986 An nla

for significance of the kelp x year interaction indicates that the interaction term was insignificant and

was deleted from the final program run Fish density is evaluated as log (s1000 m-3 + c) and kelpdensity as raw s100 m-2

ANCOV A statisticsLife Kelp

Species2 stage effect Kelp Year Kelp x year df ModelR

Atherinops affinis ALL ns - 033 599 891 153 0175

Brachyistius frenatus ALL + 071 010 4708 153 0735

Chromis punctipinnis J + 422 016 nla 166 0084

ALL + 990 bullbull 058 nla 166 0185 bullbullbull

Embiotoca jacksoni S + 1259 049 596 1690345 bullbullbull

A + 520 016 1639bullbull 169 0436 bullbullbull

ALL + 2015 125 889 169 0460

Haichoeres semicinctus J + 3129 bullbullbull 03 487 169 0497 bullbullbull

S + 775 bullbull 2635 bullbullbull nla 170 0277 bullbullbull

A + 1617 4197 nla 170 0385 bullbull

ALL + 1497 3483 nla 170 0346

Heterastichus rostratus J + 484 634 n l a 166 0108

S ns + 070 079 2605 bullbull 165 0447

ALL ns + 155 017 1847 165 0399

Hypsurus caryi S + 624 389 nla 170 0094

A ns + 021 090 1107 169 0205

ALL ns + 161 019 1020 169 0255 Medialuna californiensis S ns 03 135 n l a 154 0059

A ns 004 5776 n l a 154 0649

ALL ns 000 4464 nla I 54 0582

Oxyjuis califarnica J + 670 624 nla 166 0122

S + 912 021 394 165 0280

A + 4503 2584 n l a 166 0439

ALL + 4487 2179 nla 166 0428

Paralabrax c1athratus YOY + 660 361 407 165 0366

OJ + 1493 503 656 165 0486

J + 2040 616 739 165 0534

S + 381 675 488 165 0445

A ns + 005 005 1161 165 0329ALL + 1355 864 548 165 0512

Paralabrax nebulifer J ns + 226 035 1966 169 0391

S + 1095 1042 nla 170 0176

A ns 025 1122 n l a 170 0184

ALL + 1315 1781 n l a 170 0238

Phanerodan furcatus S + 879 241 n l a 166 0119

A + 717 229 nla 166 0101

ALL + 1002 160 nla 166 0132

Rhacochilus vacca S + 1436 182 n l a 170 0171

A ns + 195 007 1532 169 0353

ALL + 2086 609n l a

170 0232Semicossyphus pulcher J ns + 015 504 412 169 0383

S ns 030 008 nla 170 0004

ALL ns 116 2308 nla 1 70 0257

Analyses evaluated fish density and kelp density at five stations during each of two fan seasons (1985 1986 see Methods) Regionalmeans are summarized for each station and year in Appendix Table I2 The water-column-strata utilized depended on the species of fish (see Methods and Appendix Table 1)middot005 gt Pgt 001middotmiddot001 gt Pgt 0001middot P lt 0001



DEMARTINI AND ROBERTS KELP EFFECTS ON FISHES 291

Table 2 Results of ANCOVAs testing the effects of kelp density on fish density at San Onofre Kelpbed during fall 1985 and fall 1986 Fall period is analyzed as the variable year fish density is

evaluated as (A) numbers and (B) biomass expressed as log (x per 1000 m) Analyses use (I) all kelpdata (Fig I) (2) kelp densities 15 plantsmiddot 100-2 only and (3) kelp densitiesgt I plantmiddot 100 m-2 only

Model R2S are also noted

Fish density

(A) Numbers (B) Biomass

Model ModelKelp data used Source df F Prgt F R F Prgt F R

(1) All kelp Model 3 1892 047 2063 049

Year I 1028 1548

Kelp I 2500 1984

Yr x KJp I 110 030 070 040Total 68

(2) 15100 m2 Model 3 1606 050 1763 052Year I 941 755

Kelp I 752 053 047Yr x KJp I 002 090 175 019

Total 53

(3) gt 1100 m2 Model 3 960 035 1380 044

Year I 848 1465

Kelp I 530 860

Yr x KJp I 001 093 027 060

Total 57

middot005 gt Pgt 001middotmiddot001 gt Pgt 0001 bullbullbull P lt 0001

affinis halfmoon Medialuna californiensis and California sheephead Semicos-syphus pulcher) were unrelated to Macrocystis (Table 1)

When density data are pooled for all 14 select fish species both numerical andbiomass fish densities are positive functions of kelp density if the fish-kelp re-lationship is evaluated using all the kelp data available in each year (Fig 1) Bothmeasures of fish density are greater in 1986 (Table 2) If re-evaluated for a max-imum kelp density of IS plants 100 m -2 (the greatest kelp density common toboth years) fish density (numbers) is positively related to kelp density in 1985as well as 1986 and the overall level offish density remains greater in 1986 (Table

2) IfIimited to kelp densities of ~ 15 plants 100 m-2 the slope of the regressionfor fish biomass though becomes insignificant in 1985 (Table 2) Ifkelp densitiesof lt1 plant middot100 m-2 only are excluded from re-analysis (as a test of a potentialthreshold effect of kelp presence on fish) the relation between fish density (bothnumbers and biomass) and kelp density remains significant (Table 2) The larger

y-intercepts of the 1986 plots of fish density versus kelp density clearly illustratethat fish were more concentrated at the lower yet maximum available kelpdensities that occurred in the second fall (Table 2 Fig lA B)

Fish Abundances -Approximately 225000 fish weighing over 18000 kg werepresent at SOK during fall 1985 The respective estimates in fall 1986 were nearly

397000 fish weighing almost 39000 kg (Table 3) A majority of the 14 selectspecies as well as total fishes was significantly more abundant during the secondfall period (Table 3) Three labrids (senorita Oxyjulis californica California sheep-

head and rock wrasse Halichoeres semicinctus) together contributed 62-74(numbers) and 44-65 (biomass) to total fish stocks then present at SOK Senorita

in particular dominated the fish assemblage (numbers 55-63 biomass 36-39) All 14 select species comprised 88 of total fish abundance in fall 1985and 75 (biomass) to 80 (numbers) of total abundance iIi fall 1986 (Table 3)




(A) NUMERICAL DENSITY

4

El-GEl 1986YEAR - 1985

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1o 10 20 30

(B) BIOMASS DENSITY

6

~

ooo

5

~CJ)

zwo

o o

3

o 10 20

MACROCYSTIS DENSITY

30



DEMARTINI AND ROBERTS KELP EFFECfS ON FISHES 293

DISCUSSION

Fish-Kelp Density Relations -Macrocystis density had frequent and large positiveeffects on the density of fishes (Table 1) Among all the species tested howeverperhaps only one case (kelp perch) represents an obligate relationship (Ebelingand Laur 1988 and references) The remaining positive associations between fishand kelp likely represent a variety of direct and indirect influences of kelp on fish

Positive kelp effects generally prevailed for all post-recruit stages of species thatwere associated with giant kelp (Table I) The observed positive effects of Macro-cystis on older juveniles and subadults as well as younger juvenile kelp bass areworth contrasting with the findings of other researchers elsewhere At Santa Cat-alina Island giant kelp provides a necessary resource for younger juvenile kelpbass (Carr 1989)-she1ter that is perhaps unnecessary for large-bodied bass(Holbrook et al in press) We suggest that shelter and other resources provided

by Macrocystis at SOK are more important for kelp bass of a greater size rangebecause of the relative scarcity of other habitat structure at SOK This point isgenerally discussed below

Other notable fish-kelp effects are the pervasive positive associations between Macrocystis and the bottom-dwelling embiotocid surfperches Relationships be-tween kelp and surfperch may represent strong although indirect linkages in-volving kelp (as a major source of detrital food for the benthic crustacean preyof surfperch) and these fishes (Ebeling and Laur 1988) Our data suggest thatthese relations may importantly influence surfperch distributions within kelp bedsas well as affect the regional abundance of surfperch via the exportation of drift

kelp fated to be detritus (Ebeling and Laur 1988)Several of the insignificant fish-kelp relations may have been real but unde-

monstrable relationships For example density estimates for halfmoon a patch-ily-distributed schooling species had such high variances and low power thatdetecting anything less than an overwhelming relation with giant kelp was im-possible Any fish-kelp relation for topsmelt likely was overwhelmed by a spatial

effect reflecting high densities both years at one station of intermediate kelp density(pers obs)

It is important to note that these fish-kelp relationships were observed at a time

when kelp densities at SOK had begun to rebound (in 1985) following gt90

reductions in densities and an almost complete loss of surface canopy (J ReitzelECOSystems Management Associates Inc Encinitas California unpubl report)due to nutrient limitation and severe storm disturbance during the California

El Nino of 1982-1984 (Tegner and Dayton 1987 and references) In the fall of

1985 the average density of kelp at SOK was -6 plants 100 m-2 and an estimated70000 kelp plants then occupied about 113 ha (Table 4) By the fall of 1986average kelp density at SOK had been halved again by storm disturbance duringthe winter of 1985-1986 and over one-halffewer kelp plants then occupied only

about 88 ha (Table 4) Sparse kelp occupied -60 of SOK during each fall butthe area of high-density kelp was less than half as extensive in fall 1986 (Table

4) The observed fish-kelp relations thus span a range of kelp densities that areless than known maxima at SOK the greatest densities observed in this study

+-

Figure I Scatterplot of the relation between the (A) numerical and the (B) biomass (g) densities of

fish versus the density of giant kelp at San Onofre Kelp bed during fall 1985 and fall 1986 Fish

densities represent the sum of all post-recruit life stages of the 14 major species evaluated Lines

represent the best fit by least squares linear regression as described by the respective equation




- - -ono0

c i- bull bullbullbullon

0 -lJ)oo

00 0 00 0 000

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~ V r- ~ N ~~ ~ ~ D

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DEMARTINI AND ROBERTS KELP EFFEcrS ON FISHES 295

Table 4 Absolute and percentage areal contributions of various kelp density regions within San

Onofre Kelp bed during fall 1985 and fall 1986 Also noted are grand mean densities and estimated

bedwide abundances of giant kelp during each period Estimates are based on the data of Reitzel(Ecosystems Management Associates Inc unpubl report)

Fall 1985 Fall 1986

Kelp density regiont Area (ha) Area (ha)

High 29 26 5 6Intermediate 18 15 29 33Sparse 66 59 54 61

Total kelp bed 113 100 88 100

Weighted mean density 6100 m 3100 mBedwide abundance 70000 30000

t In fall 1985 the three kelp density regions were high = gt 16 plantsmiddot 100 m- intennediate = 4-16 plantsmiddot 100 m and sparse = lt4plants 100 m- In fall 1986 the three regions were high = gt8 plants 100 m- intennediate = 2-8 pLants 100 m- and sparse = lt2

plants 100 m-

were about 22 plants 100 m-2 (Appendix Table 1) whereas maxima of more than30 plants 100 m-2have been observed previously at SOK (Larson and DeMartini1984)

The nature of the bottom substrate in the SOK bed importantly affects inter-pretation of our fish-kelp data The SOK bed is anchored on a low-relief cobblesubstrate Choosing a kelp bed on low-relief substrate has allowed us to factorout substrate heterogeneity (from the structural effects of kelp near bottom) bysampling design (Larson and DeMartini 1984) The SOK bed though is unlike

most other forests of giant kelp in southern California waters that are attached toconsolidated rock substrates with varying degrees of physical relief(Quast 1968aFeder et a1 1974 Ebeling et a1 1980a 1980b Stephens et a1 1984 Patton eta1 1985) Because of the relatively unstable nature of cobble bottoms the averageage and size of kelp plants attached to cobble probably are less than the age andsize of plants anchored on more persistent bedrock and boulder substrates Con-sequently our numeric relations between the densities offish and giant kelp maybe relevant only to other cobble-bottom kelp beds

The cobble seabed at SOK probably affects fish densities there in two specificcomplementary ways (1) Low-relief seabeds provide less structural heterogeneity

than highly three-dimensional rocks and boulders on temperate reefs (Quast1968a Helvey and Smith 1985 Patton et a1 1985) and the diversity and den-sities of benthic fishes are enhanced on rugose reefs (Ebeling et a1 1980a fig 3Helvey and Smith 1985 Patton et a1 1985) Forests of giant kelp provide ad-

ditional structure and extension of benthic habitat (Quast 1968a Feder et a11974 Foster and Schiel 1985 Bodkin 1986 1988) and additional structure isdisproportionately important on low-relief seabeds (Larson and DeMartini 1984this study) (2) Because of the lack of rocky crevices that provide shelter thespecies of fishes that dominate the assemblage at the SOK bed are those that canoccupy the least specialized reef habitats except for species (like kelp perch) that

are highly specialized for the kelp canopy (Quast 1968a Federet a1 1974 Ebelinget a1 1980a 1980b Allen 1985 Helvey and Smith 1985 Patton et a1 1985)The most indiscriminate of these fishes inhabited regions of sparse kelp (Appendix

Table 1 Hobson and Chess 1986) Many species of fishes at SOK being less tiedto benthic shelter apparently respond more strongly to development of water-column habitat than obligate crevice-dwellers in rugose-bottom kelp beds (Ap-

pendix Table 1 Ebeling et a1 1980a Larson and DeMartini 1984 and referencesBodkin 1986 1988) Certainly an important general function of giant kelp



2 96 BULLETIN OF MARINE SCIENCE VOL 46 NO2 1990

particularly on low-relief cobble bottoms such as at SOK is the provision of vertical relief (Quast 1968a Foster and Schiel 1985 Bodkin 1986 Schiel andFoster 1986)

The vertical habitat structure of kelp forests surely provides multiple resourcesfor fishes Coyer (1984) has documented the diverse crustacean prey of fishesfound in midwater and canopy as well as holdfast and other near-bottom areaswithin Macrocystis forests Other studies have emphasized the importance of therefuging resources provided by submerged algal stands both for fishes as prey(Ebeling and Laur 1985 Choat and Ayling 1987) and for the prey of these fishes(Holbrook and Schmitt 1984 Schmitt and Holbrook 1986) However all studiesof refuging thus far with the notable exceptions of those by Carr (1983 1989)have been limited to evaluations of subcanopy and benthic understory algae withinkelp forests

The present study and other experimental demonstrations in particular (Bod-kin 1988 Carr 1983 1989) illustrate the general functional importance of Ma-crocystis to rocky inshore fishes It is likely that habitat structure provided by thewater-column foliage and floating surface canopy of giant kelp is one major ele-ment that is involved Comprehensive quantitative studies of both food and

shelter resource spectra and their likely important interactions in Macrocystis

forests (Moreno and lara 1984) are still needed

Fish-Kelp Abundance Relations -During fall 1986 at SOK more fishes werepresent (and concentrating at greater densities) within a kelp bed that occupied

less area and that comprised fewer more scattered kelp plants than were present

in fall 1985 Thus the generally positive fish-kelp density relations that we observedpersisted during both years despite approximately two-fold differences betweenyears in the overall level of fish abundance Pervasive year (intercept) effectsillustrate the latter (Table 2 Fig lA B)

Too few data exist for us to do more than briefly speculate on the mechanismsinfluencing bedwide fish abundances at SOK Causes of changes in overall abun-dance levels might have been local (within-kelp bed) or large-scale (eg as large

as the entire Southern California Bight) Perhaps lagged numerical responses suchas those following enhanced juvenile recruitment of labrids and other warm-

temperate fishes during the 1982-1984 El Nino (Cowen 1985) were involved

Despite the year differences in kelp and fish abundances the rate of increase infish density per unit kelp density did not differ between years-ie all kelp-by-

year interactions were insignificant (Table 2 Fig lA B) These observations bothencourage and discourage future attempts at mathematically describing fish-kelp

density relations On the one hand our data suggest that rates of change in fish

density relative to kelp density might be similar within a particular kelp bed (or

within one type of kelp bed) over time On the other hand it seems probable thatfish abundances in general fluctuate greatly over time within single stands of kelpThus a single description of fish-kelp relations for a particular kelp bed mighterroneously describe such relations for the same kelp bed at another time Mea-

sures of fish-kelp density relations are needed at many more (and different typesof) kelp beds before generalizations about fish-kelp relations are warranted Our

study also illustrates the added need for repeated characterizations at specific kelp

forests

ACKNOWLEDGMENTS

We thank T Anderson R Fountain and F Koehm for field assistance J Callahan for statistical

advice and A Ebeling R Larson and several anonymous reviewers for constructive criticisms This



DEMARTINI AND ROBERTS KELP EFFECfS ON ASHES 297

paper is the result of research conducted for the Marine Review Committee (MRC) Encinitas Cal-

ifornia The MRC does not necessarily accept the results findings or conclusions presented herein

LITERATURE CITED

Allen L J 1985 A habitat analysis of the nearshore marine fishes from southern California Bull

So Calif Acad Sci 84 133-155

Bailey N T 1981 Statistical methods in biology Second edition John Wiley and Sons New York216 pp

Bernstein B B and N Jung 1979 Selective pressures and coevolution in a kelp canopy communityin southern California Ecol Monogr 49 335-355

Bodkin J L 1986 Fish assemblages in Macrocystis and Nereocystis forests off central California

Fish Bull US 84 799-808

--- 1988 Effects of kelp forest removal on associated fish assemblages in central California JExp Mar Bior Ecol 117 227-238

Bray R N and A W Ebeling 1975 Food activity and habitat of three picker-type microcar-

nivorous fishes in the kelp forests off Santa Barbara California Fish Bull US 73 815-829Carr M H 1983 Spatial and temporal patterns of recruitment of young-of-the-year rockfishes

(genus Sebastes) into a central California kelp forest MA Thesis San Francisco State University95 pp

--- 1989 Effects of macro algal assemblages on the recruitment of temperate zone reef fishes JExp Mar BioI Ecol 126 59-76

Choat J H and A M Ayling 1987 The relationship between habitat structure and fish faunas on

New Zealand reefs J Exp Mar BioI Ecol 110 257-284

Cowen R K 1985 Large scale pattern of recruitment by the labrid Semicossyphus pulcher causes

and implications J Mar Res 43 719-742Coyer J A 1979 The invertebrate assemblage associated with Macrocystis pyrifera and its utilization

as a food resource by kelp forest fishes PhD Thesis Univ Southern California Los Angeles364 pp

--- 1984 The invertebrate assemblage associated with the giant kelp Macrocystis pyrifera atSanta Catalina Island California general description with emphasis on amphipods copepods

mysids and shrimps Fish Bull US 82 55-66DeMartini E E D A Roberts and T W Anderson 1989 Contrasting patterns offish density and

abundance at an artificial rock reef and a cobble-bottom kelp forest Bull Mar Sci 44 881-892

Ebeling A W and D R Laur 1985 The influence of plant cover on surfperch abundance at anoffshore temperate reef Environ BioI Fish 12 169-179

--- and --- 1988 Fish populations in kelp forests without sea otters effects of severe storm

damage and destructive sea urchin grazing Pages 169-191 in G R VanBlaricom and J A Esteseds The influence of sea otters on the nearshore marine ecosystem in the North Pacific Springer-Verlag Berlin FRG

--- R J Larson and W S Alevizon 1980a Habitat groups and island-mainland distribution

of kelp-bed fishes off Santa Barbara California Pages 403-431 in D M Power ed The CaliforniaIslands Proceedings ofa Multidisciplinary Symposium Santa Barbara Museum of Natural His-

tory

-- -- -- and R N Bray 1980b Annual variability of reef fish assemblages in kelp

forests off Santa Barbara California Fish Bull US 78 361-377

Feder H M C H Turner and C Limbaugh 1974 Observations on fishes associated with kelp

beds in southern California Calif Dep Fish Game Fish Bull 160 144 pp

Foster M S and D R Schiel 1985 The ecology of giant kelp forests in California US Fish Wildl

Serv BioI Servo Progr Wash DC 287 pp

Helvey M and R W Smith 1985 Influence of habitat structure on the fish assemblages associated

with two cooling-water intake structures in southern California Bull Mar Sci 37 189-199

Hobson E S and J R Chess 1976 Trophic interactions among fishes and zooplankters near shore

at Santa Catalina Island California Fish Bull US 74 567-598

--- and --- 1986 Relationships among fishes and their prey in a nearshore sand community

off Southern California Environ BioI Fish 17 201-226

--- W L McFarland and J R Chess 1981 Crepuscular and nocturnal activities of Californian

nearshore fishes with consideration oftheir scotopic visual pigments and the photic environment


Holbrook S J and R J Schmitt 1984 Experimental analyses of patch selection by foraging black

surfperch (Embiotocajacksoni Agassiz) J Exp Mar BioI Ecol 79 39-64

-- M H Carr R J Schmitt and J A Coyer In press The effect of giant kelp on local abundance

of demersal fishes the importance of ontogenetic resource requirements Bull Mar Sci



298 BULLETINOF MARINESCIENCEVOL46 NO2 1990

Larson R L and E E DeMartini 1984 Abundance and vertical distribution of fishes in a cobble-

bottom kelp forest off San Onofre California Fish Bull US 82 37-53

Moreno C A and H F Jara 1984 Ecological studies on fish fauna associated with Macrocystis

pyrifera belts in the south of Fuegian Islands Chile Mar Ecol Progr Ser 15 99-107

North W J (ed) 1971a The biology of giant kelp beds (Macrocystis) in California Nova HedwigiaBeihefte 32 600 pp

-- 1971b Introduction and background Pages 1-92 in W J North ed The biology of giantkelp beds (Macrocystis) in Califomia Nova Hedwigia Beihefte 32

Patton M L R S Grove and R F Harman 1985 What do natural reefs tell us about designingartificial reefs in southern California Bull Mar Sci 37 279-298

Quast J C 1968a Fish fauna of the rocky inshore zone Calif Dep Fish Game Fish Bull 139

35-55--- 1968b Estimates of the populations and standing crop of fishes Calif Dep Fish Game

Fish Bull 139 57-79--- 1968c Observations on the food of the kelp-bed fishes Calif Dep Fish Game Fish Bull

139 109-142

Schiel D R and M S Foster 1986 The structure of subtidal algal stands in temperate watersAnn Rev Oceanogr Mar BioI 24 265-307

Schmitt R J and S 1 Holbrook 1986 Seasonally fluctuating resources and temporal variabilityof interspecific competition Oecologia (Ber) 69 I-II

Statistical Analysis System (SAS) 1985 SAS users guide statistics Version 5 edition SAS Institute

Inc Cary North Carolina 456 pp

Stephens J S Jr P A Morris K Zerba and M Love 1984 Factors affecting fish diversity on a

temperate reef the fish assemblage of Palos Verdes Point 1974-1981 Environ BioI Fish II

259-275Tegner M J and P K Dayton 1987 EI Nino effects on southern California kelp forest communities

Adv Eco Res 17 243-279

DATEACCEPTED January 24 1989

ADDRESS (EED) Marine Review Committee Research Center 531 Encinitas Boulevard Suite 105

Encinitas California 92024 (DAR) Science Applications International Corporation 10260 Campus

Point Drive San Diego California 92122 PRESENTADDRESS(EED) National Marine Fisheries

Service NOAA Southwest Fisheries Center 2570 Dole Street Honolulu Hawaii 96822-2396




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most of which resulted from loss of kelp habitat due to storm damage and urchingrazmg

In this paper we relate the density of fishes to the density of giant kelp (Macrocys-

tis pyrifera) anchored on a low-relief cobble seabed One objective is to extendLarson and DeMartinis (1984) evaluation of fish-kelp relations at this kelp bedto include all post-recruit life stages of major fish species present during twosubsequent but consecutive fall seasons of observation A second objective is toestimate bedwide fish abundances during each period of study and to contrastpatterns of density and abundance for fish and for kelp

MATERIALS AND METHODS

Study Area - We conducted this study in San Onofre Kelp bed (SOK) a forest of giant kelp Macrocystis

pyrifera anchored on a low relief ( lt I-m high) cobble bottom offshore of San Onofre northern SanDiego County California (Larson and DeMartini 1984 fig I) Stations sampled were in the middle

and offshore regions of the kelp bed 2 to 3 km from shore in 12-18 m of water Average bottom

depth sampled was 145 m

Fish Sampling Methods-Methods described herein generally follow those of Larson and DeMartini

(1984) Fish densities were estimated in two ways depending on the vertical stratum being sampled

On and near bottom fish densities were estimated directly by divers visual counts Fishes were

counted on belt transects as transect lines were paid out on swims radiating from fixed station hubs

Transect bearings were selected randomly from within arcs of permissible kelp habitat In midwater

and just below the surface canopy we used Super-8 cine transects to record fish observations for

later tallying of fish (Ebeling et aI 1980a 1980b) Cinetransects were swum along random bearings

within permissible arcs but lines were not used Divers swam at relatively constant rates filming

continuously while panning across observed fish until the film cartridge was exhausted (about 3 min)

Six-bottom two-midwater and eight-canopy transects were sampled per survey (date) at a station

For all species except one fish were scored as one of three size-specific maturity stages (J = juvenile

S = subadult A = adult) on in situ diver counts and film tallies Juvenile kelp bass (Paralabrax

clathratus) were further classified into young-of-year (YOY) and older juveniles (OJ) Stages were

recognized based on estimated total length (TL) in inches and a defined size-maturity relation for the

species For fish that averaged 15 to 30 em (6 to 12 in) TL the error of divers estimates was -211 2

em (s I in) based on the results of practice surveys where divers estimated the lengths of preserved

fish tethered along transect lines (E DeMartini unpubI data)

Dimensions of transects were either fixed (bottom) or variable but estimable (midwater and surface)

All bottom transects were 3-m wide by I5-m high by 75-m long (225 m2 area 3375 m3 volume)

Fish counts on bottom transects were standardized to number 1000 m-3bull Dimensions of midwater

(76-m depth) and surface canopy (3I-m depth) transects depended on lateral underwater visibility

Film counts were standardized to a volume of 1000 m3 Filmed at a swimming speed of 25 mminthe 3-min cinetransects were about 75-m long Data were collected during daylight (0800-1600) when

average lateral underwater visibility was 25 m

We estimated densities for each maturity stage of 14 species selected on the basis of adequate

abundance and frequency of occurrence in samples Densities were integrated over the water column

by weighting for the thickness of each relevant sampling stratum Stratum thickness was determined

by boundaries that extended midway between sampling depths (surface canopy 53 m midwater 77

m bottom 15 m) Relevant strata differed among species depending on whether the species inhabited

the canopy bottom midwater or was cosmopolitan in its distribution (Appendix Table I)

The length frequency distributions of fishes were characterized on timed random searches that

complemented our transect swims All fish encountered during these searches were classified by species

and size-class (TL in inches) Totals of 1800 min and 1360 min were spent characterizing length

distributions in 1985 and 1986 respectively DeMartini et aI (1989) provide additional detailsData were collected at five stations during the normally clear-water period (October-December) of

1985 and 1986 Surface canopy midwater and bottom microhabitats were usually sampled during a

single day at each station All stations could not be sampled on the same day however A team of

the same four divers conducted from four to eight surveys at each ofthe five stations during each fall

period (Appendix Table I)

Station positions were chosen based on the density of giant kelp Two stations were located in

regions of highest existing Macrocystis density one station in sparse kelp and two stations in regions

of intermediate kelp density In fall 1985 the two stations in densest available kelp averaged 20-22

plants 100 m-2 and the intermediate stations averaged 8-10 plants 100 m-2bull In fall 1986 kelp


































REsULTS




















ALL + 2015 125 889 169 0460



A + 1617 4197 nla 170 0385 bullbull

ALL + 1497 3483 nla 170 0346


S ns + 070 079 2605 bullbull 165 0447

ALL ns + 155 017 1847 165 0399


A ns + 021 090 1107 169 0205


A ns 004 5776 n l a 154 0649

ALL ns 000 4464 nla I 54 0582


S + 912 021 394 165 0280

A + 4503 2584 n l a 166 0439

ALL + 4487 2179 nla 166 0428


OJ + 1493 503 656 165 0486

J + 2040 616 739 165 0534

S + 381 675 488 165 0445

A ns + 005 005 1161 165 0329ALL + 1355 864 548 165 0512


S + 1095 1042 nla 170 0176

A ns 025 1122 n l a 170 0184

ALL + 1315 1781 n l a 170 0238


A + 717 229 nla 166 0101

ALL + 1002 160 nla 166 0132


A ns + 195 007 1532 169 0353

ALL + 2086 609n l a


S ns 030 008 nla 170 0004

ALL ns 116 2308 nla 1 70 0257








Fish density



(1) All kelp Model 3 1892 047 2063 049

Year I 1028 1548

Kelp I 2500 1984

Yr x KJp I 110 030 070 040Total 68

(2) 15100 m2 Model 3 1606 050 1763 052Year I 941 755

Kelp I 752 053 047Yr x KJp I 002 090 175 019

Total 53

(3) gt 1100 m2 Model 3 960 035 1380 044

Year I 848 1465

Kelp I 530 860

Yr x KJp I 001 093 027 060

Total 57














4


o

o

3

~CJ)

zwo

1o 10 20 30

(B) BIOMASS DENSITY

6

~

ooo

5

~CJ)

zwo

o o

3

o 10 20

MACROCYSTIS DENSITY

30




DISCUSSION















+-








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Fall 1985 Fall 1986






plants 100 m-































forests

ACKNOWLEDGMENTS








LITERATURE CITED

























tory

































139 109-142

















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REsULTS




















ALL + 2015 125 889 169 0460



A + 1617 4197 nla 170 0385 bullbull

ALL + 1497 3483 nla 170 0346


S ns + 070 079 2605 bullbull 165 0447

ALL ns + 155 017 1847 165 0399


A ns + 021 090 1107 169 0205


A ns 004 5776 n l a 154 0649

ALL ns 000 4464 nla I 54 0582


S + 912 021 394 165 0280

A + 4503 2584 n l a 166 0439

ALL + 4487 2179 nla 166 0428


OJ + 1493 503 656 165 0486

J + 2040 616 739 165 0534

S + 381 675 488 165 0445

A ns + 005 005 1161 165 0329ALL + 1355 864 548 165 0512


S + 1095 1042 nla 170 0176

A ns 025 1122 n l a 170 0184

ALL + 1315 1781 n l a 170 0238


A + 717 229 nla 166 0101

ALL + 1002 160 nla 166 0132


A ns + 195 007 1532 169 0353

ALL + 2086 609n l a


S ns 030 008 nla 170 0004

ALL ns 116 2308 nla 1 70 0257








Fish density



(1) All kelp Model 3 1892 047 2063 049

Year I 1028 1548

Kelp I 2500 1984

Yr x KJp I 110 030 070 040Total 68

(2) 15100 m2 Model 3 1606 050 1763 052Year I 941 755

Kelp I 752 053 047Yr x KJp I 002 090 175 019

Total 53

(3) gt 1100 m2 Model 3 960 035 1380 044

Year I 848 1465

Kelp I 530 860

Yr x KJp I 001 093 027 060

Total 57














4


o

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zwo

1o 10 20 30

(B) BIOMASS DENSITY

6

~

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5

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zwo

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3

o 10 20

MACROCYSTIS DENSITY

30




DISCUSSION















+-








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Fall 1985 Fall 1986






plants 100 m-































forests

ACKNOWLEDGMENTS








LITERATURE CITED

























tory

































139 109-142

















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ALL + 2015 125 889 169 0460



A + 1617 4197 nla 170 0385 bullbull

ALL + 1497 3483 nla 170 0346


S ns + 070 079 2605 bullbull 165 0447

ALL ns + 155 017 1847 165 0399


A ns + 021 090 1107 169 0205


A ns 004 5776 n l a 154 0649

ALL ns 000 4464 nla I 54 0582


S + 912 021 394 165 0280

A + 4503 2584 n l a 166 0439

ALL + 4487 2179 nla 166 0428


OJ + 1493 503 656 165 0486

J + 2040 616 739 165 0534

S + 381 675 488 165 0445

A ns + 005 005 1161 165 0329ALL + 1355 864 548 165 0512


S + 1095 1042 nla 170 0176

A ns 025 1122 n l a 170 0184

ALL + 1315 1781 n l a 170 0238


A + 717 229 nla 166 0101

ALL + 1002 160 nla 166 0132


A ns + 195 007 1532 169 0353

ALL + 2086 609n l a


S ns 030 008 nla 170 0004

ALL ns 116 2308 nla 1 70 0257








Fish density



(1) All kelp Model 3 1892 047 2063 049

Year I 1028 1548

Kelp I 2500 1984

Yr x KJp I 110 030 070 040Total 68

(2) 15100 m2 Model 3 1606 050 1763 052Year I 941 755

Kelp I 752 053 047Yr x KJp I 002 090 175 019

Total 53

(3) gt 1100 m2 Model 3 960 035 1380 044

Year I 848 1465

Kelp I 530 860

Yr x KJp I 001 093 027 060

Total 57














4


o

o

3

~CJ)

zwo

1o 10 20 30

(B) BIOMASS DENSITY

6

~

ooo

5

~CJ)

zwo

o o

3

o 10 20

MACROCYSTIS DENSITY

30




DISCUSSION















+-








- - -ono0


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00 0 00 0 000

~oONltgt

- - -bull - IIt----


~ V r- ~ N ~~ ~ ~ D

(I 00-- -

on

on

~0el

Z







Fall 1985 Fall 1986






plants 100 m-































forests

ACKNOWLEDGMENTS








LITERATURE CITED

























tory

































139 109-142

















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88 ~88 ~66d 8~~ 88800 -Nfll _1)-0 0__ 0--

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= = =~ 0 do NNe8i~~~888N 00 0r-ooooo

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Fish density



(1) All kelp Model 3 1892 047 2063 049

Year I 1028 1548

Kelp I 2500 1984

Yr x KJp I 110 030 070 040Total 68

(2) 15100 m2 Model 3 1606 050 1763 052Year I 941 755

Kelp I 752 053 047Yr x KJp I 002 090 175 019

Total 53

(3) gt 1100 m2 Model 3 960 035 1380 044

Year I 848 1465

Kelp I 530 860

Yr x KJp I 001 093 027 060

Total 57














4


o

o

3

~CJ)

zwo

1o 10 20 30

(B) BIOMASS DENSITY

6

~

ooo

5

~CJ)

zwo

o o

3

o 10 20

MACROCYSTIS DENSITY

30




DISCUSSION















+-








- - -ono0


0 -lJ)oo

00 0 00 0 000

~oONltgt

- - -bull - IIt----


~ V r- ~ N ~~ ~ ~ D

(I 00-- -

on

on

~0el

Z







Fall 1985 Fall 1986






plants 100 m-































forests

ACKNOWLEDGMENTS








LITERATURE CITED

























tory

































139 109-142

















~ ---

01)1)

~e8e-vv0000

~~0008v v

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0 0 V V

~ - - ----


~~~666 6 ~ ~~~r-888 ~~~ 88ii000 _ a- 000

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66 s-=- S=-~N 868 86S

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00000 oto 000 000

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88 ~88 ~66d 8~~ 88800 -Nfll _1)-0 0__ 0--

0000000000000V - V V

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= = =~ 0 do NNe8i~~~888N 00 0r-ooooo

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Demartini and Roberts 1990 Effects of Kelp on Fish Density

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Transcript of Demartini and Roberts 1990 Effects of Kelp on Fish Density