Structural aspects of the surf-zone fish assemblage at King's Beach, Algoa Bay, South Africa: Long-term fluctuations

Estuarine, Coastal and Shelf Science (1984) 18. 459-483

Structural Aspects of the Surf-zone Fish Assemblage at King’s Beach, Algoa Bay, South Africa: Long-term Fluctuations

Theresa A. Lasiaka Department of Zoology, University of Port Elizabeth, Elizabeth,

I? 0. Box 1600, Port

South Africa 6000

Received 19 November 1982 and in revisedform 29July 1983

Keywords:

fish; community;

surf zone; abundance; seasonal variations

Regular collections of fish were obtained from the surf-zone at King’s Beach, Algoa Bay. A total of 3970 fish, representing 50 species was caught with a coarse net and 16 857 fish, representing 37 species, were caught with a fine net. Predominant species were the blacktail, Dzplodus sargus; the sand steenbras, Lithognathus mormyrus; the mullet, Liza richardsoni; the gorrie, Pomadasys olivaceum; the white stumpnose, Rhabdosargus globiceps; the sandshark, Rhinobatos annulatus; and the streepie, Sarpa salpa. No seasonal trends were discernible in the overall abundance or species diversity. The species composition of the dominant component of the fish assemblage varied considerably. This indicated instability in the community structure and cast doubts on the applicability of a classic community concept and the use of diversity indices. Neither classification nor correspondence analysis were of any use in identifying a characteristic species component. Multiple regression analysis indicated that short-term variations in wind conditions might be a primary determinant of fluctuations in abundance. The lack of seasonality in the community parameters may reflect the fact that short-term variability masks seasonal perturbations.

Introduction Relatively little attention has been given to fish assemblages associatedwith beaches.This is particularly true of surf-exposed beaches,which have been avoided becauseof sampling difficulties (Schaefer, 1967). Some data are given by Pearseet al. (1942) from work done in North Carolina and extensive surveys have been reported by Gunter (1945, 1958), Carlisle et al. (1960), McFarland (1963) and Schaefer (1967). All of these emanatefrom the United States. The present study is the first attempt to examine surf-zone fish community structure, not only in South Africa but in the southern hemisphere. Investigators of fish assemblages have made no attempt to define the term ‘ community ’ and the definition adopted here is that of Menge (1976). Thus ‘ community ’ refers to a

directly or indirectly interacting assemblageof organismsoccupying a particular area or habitat. The present report is concerned with the analysisof the surf-zone fish assemblage associatedwith King’s Beach in terms of the community concept. Particular attention is ‘Present address: Department of Zoology, University of Transkei, Private Bag X5092, Umtata, Transkei, Southern Africa. 459 0272-7714/84/040459+25$03.00/0

0 1984 Academic Press Inc. (London) Limited

460

T. A. Lasiuk

given to long-term stability asmeasuredby distributional statistics-frequency, abundance and diversity. Multivariate techniques, both classification and ordination analyses, were used in an attempt to extract recurrent groups of speciesfrom the large data matrices produced. Finally, attempts were made to correlate long-term temporal variations in ‘ community structure ’ with fluctuations in various abiotic factors. Study

area

King’s Beach (33”56 ‘S, 25”39 ‘E) is the main bathing beach of Port Elizabeth; it extends 1.5 km south from the harbour (Figure 1). It is the least exposed beach in Algoa Bay,

St Fronc~s

25’34’ Figure

Bay

E

1. Map of the Port Elizabeth

area showing

the position

of King’s

Beach

being protected from the prevailing south-westerly winds by the mainland of Cape Receife. King’s Beach experiences continuous moderate wave action; waves break at a distance of 50-100 m offshore and have an average breaking height of 0.7 m (McLachlan, 1980). The surf-zone has an average width of 80 m and the break point occurs at an average depth of 2 m. The major physical, chemical and biological features have been described by McLachlan (1977, 1979, 1980). The temperate waters of Algoa Bay are subject to seasonal fluctuations with a maximum range of 1l-26 “C in the surf. Sampling

methods

The surf fish community wassampledregularly between September 1978and October 1980 by seine netting. Three hauls were taken monthly with a coarse-meshednet (40 mm stretched mesh), 60 m long and 2 m deep. Two additional hauls with a finer net (17 mm stretched mesh), 30 m long and 2 m deep with a 2 m deep purse-bag at its mid-point, were taken each month from October 1979 to October 1980. Both nets were fitted with a weighted foot rope. This arrangementthus sampledthe entire water column catching both pelagic and demersal species. Sampling was standardized with respect to both tidal and die1cycles. Preliminary hauls prior to the instigation of this study indicated poor catches during daylight hours as compared to hauls taken in the early evening. To eliminate bias

Long-term fluctuations

in a surf-zone fish assemblage

461

from photoperiodic influences seining commenced l-2 h before twilight and continued for a further l-2 h after dark. Hauls of the coarse net were made1 h before, at, and f h after, twilight. Hauls with the fine net were performed lf h before and after twilight. Sampling dates were chosen so that the times of high water were within 2 h of sunset. The seine nets were carried out to just beyond the breakpoint in an inflatable dinghy. The dinghy was slowly reversed parallel to the shoreline while the net was paid out over the side. Lengths of nylon rope were fastenedto the bridles at eachend to facilitate hauling. In the laboratory the fresh catch was sorted by speciesand the work by Smith (1965) was used as an identification reference. The total number of individuals of each specieswas recorded prior to subsamplingfor reproductive tissue and stomach analyses. Except for very abundant species, wet mass, total length and caudal length were recorded for each specimen. Data analysis Distributional

statistics

Two approacheswere usedto evaluate the abundanceof surf-zone fish. ‘ Total abundance’ refers to the total number of individuals of each speciescollected during each sampling session.Infrequent catches of certain speciesin high numbers can lead to a bias in determining importance within the assemblage.Warfel and Merriman (1944) proposed the use of ‘ relative abundance’ which emphasizesthe relative proportion of different speciesin the community in any given sampling session.Using this technique, the 10 most abundant speciesduring a given period are ranked from 10 to 1 with a decreasein abundance. Fager (1963) considered ‘ relative abundance’ to provide more information about community structure than ‘ absolute abundance‘. Species diversity was estimated by the Shannon-Wiener index modified according to Pielou (1969). This function comprisestwo components: speciesrichnessand equitability (Lloyd & Ghelardi, 1964). The former was estimated according to Margalef (1958) and the latter according to Pielou (1966a, b). All indices were calculated using logs to the base

2.

Multivariate

analyses

Classification

The monthly surveys of the surf-zone ichthyofauna were comparedby meansof ‘ inverse ’ classification analysis. This procedure groups species according to their time/site of occurrence (Clifford & Stephenson, 1975) and was used in an attempt to identify groups of co-occurrent species. The analytical procedure involves the formation of a similarity matrix based on the Bray-Curtis coefficient of similarity, followed by the clustering of speciesinto groups on the basisof the similarity matrix, and in this study the polythetic group-average clustering technique was used. Following Field (1971), logarithmic data transformation was used to tone down the dominance effects of occasional high values, prior to the formation of the similarity index. The data were subsequently represented in a dendrogram. Correspondence analysis Malmgren et al. (1978) regard correspondence analysis as a useful method of ordination

462

T. A. Lasiuk

enabling the extraction of significant patterns of interrelationships among species and samples. In this case it involved plotting units (species) on a pair of co-ordinate axes and delimiting clusters by eye (see Chardy et al., 1976). Multiple

regression

analysis

This was used to assess the combined effects of several independent (environmental) variables on each of the dependent biological variables. The BMDP 2R Multiple Stepwise Regression program was utilized in this analysis. Results Coarse net study A total of 3970 fish, representing 50 species, was caught in coarse-meshed seine hauls during the 26-month study period. On the basis of numerical abundance the five most important species, the streepie, Sarpa salpa; gorrie, Pomadasys olivaceum; moony, Monodactylus falciformis; southern mullet, Liza richardsoni; and the blacktail, Dtplodus sargus accounted for 73.7% of the total catch (Table 1). The prominence of S. salpa resulted from a large catch in July 1979 (Table 2) which alone accounted for 65.2% of all the streepies caught during the study. The same five species also predominated when ‘ relative ’ abundance was used as an indicator of dominance. However, there were differences in the order of dominance and percentage contribution to the overall catch. Using biomass as an indication of species dominance the five major species comprised 67.5% of the overall fish biomass. In order of decreasing dominance they were: the sandshark, Rhinobatos annulatus; marble ray, Dasyatis pastinacus; moony, M. falctformis; southern mullet, L. richardsoni and the baardman, Umbrina capensis (Table 1). Dasyatis pastinacus and R. annulatus contributed significantly to total biomass as a result of the influx of high numbers into the study area on a few occasions. Dasyatis pastinacus fell into 10th position on the basis of ‘ relative ’ biomass. The use of ‘ relative ’ biomass as a criterion of dominance suggests that the King’s Beach ichthyofauna was characterized by M. falciformis; R. annulatus; U. capensis; L. richardsoni and D. sargus. Discrepancies between rankings based on abundance and those based on biomass were attributed to intraspecific variations in size composition and representation of life-cycle phases in the seine hauls. No seasonal trends were discernible with respect to either the total number of individuals or biomass of fish (Figure 2). Peaks in abundance were recorded in January and July 1979 and April-May 1980. These peaks resulted from the presence of sizeable schools of one or two species. Examination of monthly catches at the species level (Table 2) indicated that large numbers of L. richardsoni and P. olivaceum were responsible for the peak in January 1979. In July 1979 S. salpa predominated, and in April 1980 large numbers of the sand steenbras Lithognathus lithognathus resulted in an enhanced abundance. Peaks in biomass were recorded in November 1978, April 1979 and April 1980. Elasmobranchs, particularly D. pastinacus and R. annulatus, were responsible for these increases. Rhinobatos annulatus and D. sargus were the most prevalent species with an occurrence of 92.3% (Table 1). Comparison of frequency of occurrence with the monthly catch data (Table 2) indicated that the 14 species with frequencies of 50% or higher were present off King’s Beach throughout the year. With the exception of Pomadasys commersonni these same species also dominated the surf-zone assemblage in terms of both ‘ total ’ and

Long-term fluctuations

TABLE

surf-zone

in a surf-zone fish assemblage

1. ’ Total ’ and ‘ relative ’ abundance fish from the coarse net study

and biomass

Abundance Total Code no. 28 26 19 29 38 15 30 31 50 47 14 13 43 24 17 37 9 8 3 1 2 20 10 4 42 46 32 33 49 40 6 5 25 48 45 34 12 11 41 34 16 35 23 12 39 27 21 36 18 7

Species

N

Amblyrhynchores honckenil Argyrosomus hololepidotus Austroglossus pectoralis Caranyx sp. Cephaloblepharus edwardsi Cheimerius nufar Coracinus capensis Coracinus multifasciatus cyn0g10ssus sp. Dasyatis pastinacus Diplodus cervinus Dtplodus sargus Halaelurus natalensis Hepsetia breviceps Heteromycteris capensis Lichia amia Lilhognathus lithognathus Lithognathus mormyrus Liza dumerili Liza richardsoni Liza rricuspidens Merluccius capensis Monodactylus falciformis Mugil cephalus Mustelus sp. Myliobatis aquila Neoscorpis lithophilus Pachymeropon blochii Pagellus natalensis Platycephalus rndicus Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Pceromylaeus bovinus Rala miraletus Raja ocellata Rhabdosargus globiceps Rhabdosargus holutn Rhinobatos annulatus Sardinops ocellata Sarpa saipa Scomber japonicus Sillago maculara Sphyraena africana Synaptura marginata Tachysurus feliceps Trachurus capensis Trzhiurus lepturus Trulla capensis Umbrina capensis

57 158 4 2 1 4 3 1 1 1 6 342 5 32 9 3 64 129 33 402 22 3 409 2 3 14 1 1 1 1 21 514 62 5 1 1 19 54 184 1 1257 1 6 7 1 3 6 4 6 67

Total

3970

1.4 4.0 0.1 0.1
and frequency

of occurrence

of

Biomass Relative

%

463

S 49.5 66.6 0 0 0 2.5 2.2 3.0 0 14.9 4.5 143.9 6.2 30.3 5.3 4.5 69.2 42.0 40.9 127.3 24.2 2.0 141.3 0 0 11.8 1.0 0 1.0 1.7 22.4 120-7 48.8 11.0 0 0.7 17.3 31.9 93.3 0.4 128.3 0 2-9 10.5 0 3.8 4.5 5.5 8.5 68.0

Total %

N.9

Relative %

3.6 2286 ‘6 0.3 4.9 39 414.0 4.7 601.7
S 13 95 2 0 0 1 3 0 0 66 5 105 6 3 7 1 75 41 16 107 34 2 160 2 12 24 4 3 0 0 86 40 59 19 0 1 4 38 158 0 76 0 1 0 0 6 3 5 0 121

% 0.9 6.8 0.1 0.1 0.2 4.7 0.4 7.5 0.4 0.2 0.5 0.1 5-3 2.9 1.1 i-6 2.4 0.1 11.4 0.1 0.9 1.7 0.3 0.2 6.1 2.9 4.2 1.4 0.1 0.3 2.7 11.3 5.4 0.1 0.4 0.2 0.4 8.6

Frequency (Percentage occurrence) 65.4 65.4 11.5 3.9 3.9 11.5 11.5 3.9 3.9 26,9 15.4 92.3 11.5 30.8 30.8 3-9 69.2 53.0 34.6 84.6 26.9 7.7 80.8 3.Y 11.5 38.5 3 Y 3.9 3.9 3.9 53.9 76.9 65.4 7-7 3-9 3-9 34 6 61.5 92.3 3.9 65.i 3.9 7.7 7-7 3.9 7-i 7.7 3.9 7 7 73.1

0 I/) c

Total

no. fish

Must&s sp. Myltobatis aquila Neoscorpis lithophilus Pachymetopon blochii Pagellus natalensis Natycephalus indicus Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Pteromylaeus bovinus Raja miraletus Raja ocellata Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annulatus Sardinops ocellara Sarpa salpa Scomber japonicus Sillago maculata Sphyraena africana Synaptura marginata Tachysurus feliceps Trachurus capensis Trichiurus lepturus T&la cape& Umbrina capensts

Species

TABLE

2.

1978

83

3

167

2

1

233

9

226

136

1 415

4

15 1

70

5

4

1

23

182

24

2

73

2

4 4 2

8

2

2

2 3

5 1

2 21 58

7

2 2

1 3 1

1 14 3

1

1 11 4

1 5 3

2 6 2

4

251

3

1

1

SONDJFMAMJJASONDJF

Conttnued

164

2

5

25

1 35

31

1

119

7

1

1 2

14 1

1

48

3

11

4

913

820

1979

8

2 6 1

1 1

50

1

6

3

6

1 1

119

2

1 34 3

90

1

1 2 1

8 12

2

43

3

1

3 2 2 2

63

3

1

68

3

10

1

5 3

1

55

1

3

1 2

L9

9

1

MAM

269

2

1

82

2 4 19

16 15

2

1 2

289

1

2

14

3

1 98 1

1

58

1 3

2

5

2 1

1

J

58

3

1 11

1

3

J

46

2

13

1 10

1

A

1 1 6

1

S

0

3 14 1 1 1 1 21 514 62 2 1 1 19 54 184 1 1257 1 6 7 1 3 6 4 6 67

rota1

466

T. A. Lasiuk

Elasmobronchs Teleosts

ond

teleosts

M

only.----0

0 1978

1979

1980 Month

Figure 2. Monthly variation in [a] the number of individuals in three consecutive hauls with the coarse-meshed net.

and [b] the mass of fish caught

‘ relative ’ abundance.Thus the characteristic ‘ resident ’ component of the King’s Beach ichthyofauna comprisesR. annulatus; D. sargus; L. richardsoni; P. olivaceum; Cr. capensis; L. lithognathus; Amblyrhynchotes honckenii; Pomatomus saltatrix; Argyrosomus hololepidotus; S. salpa; Rhabdosargus holubi and L. mormyrus. The following were spring/summer (September-February) residents:Myliobatis aquila; Liza dumerili; Rhabdosargusglobiceps; Hepsetia breviceps; D. pastinacus; Diplodus cervinus and Liza tricuspidens. The remaining

29 specieswere regarded to be of sporadic occurrence. Figure 3 illustrates monthly fluctuations in the total number of speciescaught, ShannonWiener diversity index I?, equitability and speciesrichness. No seasonaltrends were discernible. The value of fi varied from 0.75 (July 1979) to 3.66 (August 1979) with a value of 3 ‘45 estimated from the total number of fish caught per speciesover the study period. Comparisonof graphs depicting fluctuations in diversity, equitability and speciesrichness

Long-term fluctuationsin a surf-zone fkh assemblage

467

revealed the ability of the latter two componentsto influence diversity. The low diversity observed in July 1979and September 1980 was the result of reduced equitability, whereas the low diversity in March 1980 reflected low speciesrichness rather than equitability. Simple linear correlation revealed statistically significant relationships between fi and equitability (r=O.60, P
I III ’

II

I I I I I I I1

SONDJFMAMJJASONDJFMAMJJASO f :: 1978 1979

I I I I I I I I1 +

III >

< 1980

Month

Figure 3. Fluctuations in [a] the number of species caught; [b] the estimated diversity (Shannon-Wiener]; [c] the estimated equitability; and [d] the estimated species richness of the surf-zone ichthyofauna assessed from the summated catch of three consecutive hauls with the coarse-meshed net between September 1978 and October 1980.

468

T. A. Lasiuk

Percentage 100.00 I

90.00 I

60~00 I

70.00 I

60.00 I

50.00 I

slmllarlty 4000 I

30-00 I

t

20.00 I

I

I

I

I

I

I

I

I

I

90.00

80.00

70.00

60.00

50.00

40.00

30.00

20.00

clustering

0.OC 1

I 7

100.00

Figure 4. Dendrogram resulting from group-average coarse net study. Species codes given in Table 1.

IO.00 I

I

IO.00

I

1

O-CO

of species caught during

the

(Figure 5). Projections onto the first principal axis revealed no distinct groupings, the majority of species and samples being scattered across the negative side of the axis. However, projections on the second principal axis revealed a fairly discrete group on the negative side, consisting of species associated with spring/summer samples. Major components of this group were I? olivaceum; L. richardsoni; L. tricuspidens; R. globiceps and Sphyraena africana.

Projections of these samesamplesand speciesbasedon correspondenceanalysis of the biomassdata are depicted in Figure 6. A total of 36% of the variability is accounted for by projections onto the first and secondprincipal axes. Consideration of the first principal axis revealed the presenceof three discrete groups. The largest group included U. capensis; D. sargus; L. mormyrus; A. hololepidotus; R. holubi; M. falciformis; I? olivaceum; L. lithognathus; l? saltatrix; L. dumerili; M. aquila and L. richardsoni. These specieswere associ-

Long-term fluctuations

in a surf-zone&h

469

assemblage

ated with samplestaken throughout the year thus indicating no evidence of seasonality basedon biomassdata. The two smaller groups were characterized by R. annulatus and D. pastinacusrespectively. Examination of the projections onto the second principal axis confirmed the presenceof these three groups. A major feature to arise from this correspondence analysis was the fact that groupings were not very distinct, the component species tended to be well separated. No significant relationships were discernible between the various environmental parameters and log-transformed number of speciesor diversity. The total number of species caught was significantly correlated with the average wind speed for a period of 12 h prior to sampling, wind direction and photoperiod (P
l

45’

33oI*3 I

031

I

.z3 l

.4l

19

.47

I

Q49

I ,

‘22

.3

~23 19

1i7. 13.

.I0

‘12

;9””

I

026

l 6

XJ -8

‘20 r8

.24

027

IO

171

~24 A20

-7

028

125 .I8 l 38 I

Figure 5. The first and second principal axes determined by correspondence analysis of the surf-zone ichthyofauna assessed during a 26-month study period by coarse-meshed seine netting. The original data matrix was based on numerical abundance. A -Months; 0 -species.

Figure 6. The first and second principal axes determined by correspondence analysis of the surf-zone ichthyofauna assessed during a 26-month study period. The original data matrix was based on biomass. A -Months; 0 -species.

wind speed for 48 h prior to sampling. These four independent variables accounted for 41% of the variability in number of fish caught. Log-transformed biomass was significantly correlated with the average wind speed for 12 h prior to sampling, wind direction and photoperiod. These three environmental variables accounted for 39% of the variability in log mass of fish caught. Fine net study

A total of 16857 fish representing 37 specieswascaught in fine-meshedseinehaulsduring the 13-month study. On a numerical basisthe five most abundant specieswere H. breviceps; P. olivaceum; S. salpa; L. mormyrus and Trachurus capensis (Table 4). The predominance of H. breviceps was enhanced by large catches (>3000) in October and November 1979. Similarly high numbers of T. cupensis obtained in December 1979 elevated the position of this species.The predominant speciesdetermined on the basisof ‘ relative ’ abundance were the sameasthose determined by ‘ total ’ abundance. The five dominant speciesasdefined by biomassaccounted for 72.5% of the total catch. They were, in order of decreasingprominence: L. lithognathus; H. breviceps; U. capensis; Sparodon durbanensis and I? olivaceum. Differences in rankings basedon numerical abundance and biomasswere particularly noticeable with the fine net hauls. Although the fine

Long-term fluctuations

in a surf-zone&h

assemblage

471

net was more efficient in retaining small fish, it was also capable of catching larger fish. Thus a few large specimensof L. lithognathus; U. capensisand S. durbanensismay exceed the contribution madeby numerous smaller fish on the basisof mass.Using ‘ relative ’ biomassasan indicator of dominancethe five major specieswere identified to be: P. olivaceum; D. sargus;R. annulatus; L. mormyrus and L. richardsoni. Together they accounted for 45% of the points allocated (Table 4). ‘ Relative ’ biomass gives an indication of the dominance hierarchy uninfluenced by the occasionalpresence of large individuals. Thus L. lithognathus and S. durbanensis,ranked first and fourth respectively on the basisof total biomass,dropped to seventh and seventeenth place on a ‘ relative ’ biomassbasis. Monthly fluctuations in the total number of fish and biomassare given in Figure 7. The highest number of individuals was caught in October/November 1979. Numbers dropped off rapidly after this period and then increased to more than 1000 fish in October 1980. Monthly catch statistics (Table 5) indicate that large numbers of H. brevicepswere responsible for these peaks in abundance. This trend in biomassfollowed a similar pattern with a peak between October and December 1979. Three species,D. sargus,L. mormyrus and I? olivaceum, were taken throughout the study period as indicated by their frequencies of occurrence (Table 4). Comparison with the monthly catch statistics (Table 5) indicated

TABLE 3. Summary of results from multiple regression analysis of dependent biotic parameters b] against independent abiotic parameters [X,] measured during coarse net study (I is the multiple correlation coefficient, r* is the coefficient of determination, F is F-ratlo calculated by analysis of variance, C is the regression coefficient(s))

Y

Step no.

X,

(zj

F

c

No. species

1 2 3

Wind 12h Direction Photoperiod

0.50 0 56 0.64

25.1 7.71 6.7 5.13 8.9 4.80 11, l(y;in8t;rcept=20-35i)

Log-species

1 2 3

Ramfall Direction Wind 12h

0.33 0.44 o-47

1 2 3 4

Rainfall Average monthly Photoperiod Wind 48h

Log-fish

1 2 3

Wind 12h Photoperiod Direction

0.39 0.49 0.62

Mass

1 2 3 4

Direction Wind 48h Photoperiod Sea temperature

0.44 0.51 0.58 0.64

Log-mass

1 2 3

Wind12h Direction Photoperiod

0.48 0.53 0.62

Diversity

1

Wind

0.27

0.003 2.61 0 209 2.01 0.024 cv ~ intercept = 1.638’1 28.8 9.29 Z-672 5.7 5-78 44.041 3.0 4.19 -50-396 3.8 3.51 19-653 &-intercept= 323.421: 15.5 4.23 O-066 8.5 3.48 -0.139 14.2 4.34 O-367 (y-intercept: 5-5161 19.3 5.52 36 306.506 6.5 3.84 6998 -203 8.3 3.64 13983.498 6.7 3.46 4406.423 (y-intercept=71 185,339, 23.4 7.02 0.029 5.1 4.39 o- 145 10.4 4.46 0.042 (y - mtercept = 1 404; 7.1 1.77 0.77 o-intercept = 2,201:

No. fish

24h

sea temp

0.54 0.59 0.61 0.64

8.1 3.1

o-774 4.017 1.037

472

T. A. Lasiak

TABLE 4. ‘ Total ’ and ’ Relative ’ abundance zone fish from the fine net study

and biomass

Abundance ’ Total ’

frequency

55 28 26 19 29 50 14 13 52 53 54 24 17 57 37 9 8 3

I 2 10 32 49 40 6 5 25 12

11 41 16 58 22 56 51 21 7

Species

‘ Relative

’

‘ Total ’

s

%

B@:

Ambassis commersonm Amblyrhynchotes honckenii Argyrosomus hololepidotus Austroglossus pectoralis Caranx sp. cyn0g10ssus sp. Diplodus cervinus Dtplodus sargus Etrumeus terres Gtlchristella aestuarius Gonorhynchus gonorhynchus Hepsetia breviceps Heceromycteris capenszs Lepidotrigla sp. Ltchia amta Lithognathus ltthognathus Lithognathus morm?/rus Liza dumerili Liza richardsom Liza tricusprdens Monodactylus falctformis Neoszorprs lithophilus Pagellus natalensis Platycephalus indicus Pomadasys commersonm Pomadasys olrvaceum Pomatomus saltatrrx Rhabdosargus globiceps Rhabdosargus holubi Rhinobatos annularus Sarpa salpa Sparodon durbanensts Sphyraena africana Sygnathus acus Trachinotus africana Trachurus capensis Umbrina capensis Total

%

N

1 co-1 0.1

17 23

o-1

1 ‘Co.1 3 co.1 3
2.2

14 16 3 8338

0.1 O-l c-o-1 49.5

7 .O,l 6 0.1 5 LO1 20 0.1 698

4.1 8

253

1 8 2 3 1 1 5503

0.1 1.5 -to,1 0 1 0.1 0.1 CO.1 -0.1 32.6

6 ~~0.1

163 19 21

l-0 01 01

926

5-5

1 .rO-l 15 O-l 1
2-2

li

01

16857

of surf-

Biomass

Code

No.

of occurrence

0 9.6 12.3

1.4

1.7 0

07

1 5 2-i 87.0 4.8

IO.0 1-o 51.3

-

0.1 0.2

1.4 O-l

13-3

5.3 l-5 11 .8

0.7 O-2 1.7

0 5-O

0 2-o

~0.1 3.9

0.9 38060.7 78-9

0 1 10.5 K 0 1 7 5 ~0.1 39881.8 28 1 3613.0 627-2 3958-7 160.4 1831 4

-

1215 7 17-9

-

O-8 891.1

124.0 3.0 43.0 10-2

17.4 0.4 6.0

6936.8 1271 7 441 9

1.4

3731-8

15-9

2-2

6842-7

77.0

10.8 -

0 6.5

0.9

0 2
10-l ‘CO.1
13.0 o-4 9.7 07 03

0 0

4851 .O 50.2 CO.1 18.2
5.0

CO.1 0.3 3.4

o-4 12.2 0.7

7.2 O-i

93.0 2.8 69.0

0.1 369.9

%

2.5 0.4 2-8

0.1 1.3 o-9


3016.5

2.1

8759.0 40.4 0 3

6.2

1.5

6.2

676

1.9

9197.1

9

CO.1 10.1 ~0.1 0.5 6.5

’ Relative ’ Frequency ~-. (percentage S ?4l occurrence 0 7

10

40 0 2 4. 0 75 0

5.6 0.3 0.6 10.5 -

l-01 0 42 7

0 0

5.9

1 ,o -

48 53 9 50 2 34

67 7.4 1.3

10 1 0

1.4 0.1 -

i0 0.3 4.8

6

0.8

82 10

Il.5 l-4

20 30 63 42

2.8 42 8.8 59

10 2

14

0 0

o-3 -

14

2.0

49

6-9

)

i.7

61.5 46 I? 5 7 23 1

15 -1 15.4 100.0 Ii.4 i3.Y 7.7 69.2 30 8 23-l _ _ 4;.i

100 Cl 30 8 92 3 7 i

46.2

15 T 5 _

4 7 7 _

lOG 23 76 38 76

i6

I 4 i 9 9

i

7

38 5 - _ i i 7.5 76.9 53.9

142191.4

that 10 species with frequencies greater than 50% were caught throughout the year. Thus, from the fine seine hauls the ‘ resident ’ component comprised D. sargus; L. mormyrus; P. olivaceum; L. richardsoni; R. globiceps; R. annulatus; S. salpa; T. capensis; U. capensis and Gilchristella aestuarius. Members of the ‘ periodic ’ component included A. honckenii; H. breviceps; L. lithognathus and S. africana. Eighteen specieswere considered to be of

sporadic occurrence. A greater number of specieswas caught in spring and summer (September-February) (Figure 8). A distinct trough with little variation was apparent during the winter (MaySeptember 1980) while a distinct peak in diversity, fi was evident between December and

Long-termfIuctuations

in a surf-zonejish

assemblage

173

February. Calculated values of Z?ranged from 0.56 (October 1979) to 2.70 (January 1980) with an overall value of 1.99 for all samplespooled (Figure 8). Equitability showed a similar trend to diversity. Fluctuations in speciesrichness paralleled those observed in the number of speciescaught rather than diversity. Comparison, by correlation analysis, of the Shannon-Wiener function with its two components revealed a highly significant relationship between equitability and diversity (r =O. 96, P< 0 ‘05). A far lesssignificant associationwas found between speciesrichnessand diversity (r=0.47, P
Month

Figure 7. Fluctuations in [a] the number of individuals caught and [b] the mass of fish taken at monthly intervals between October 1979 and October 1980 with the fine-meshed net.

T. A. Lasiak

474

-7

E

Long-term jluctuations

475

in a surf-zone fish assemblage

01 ONDJFMAMJJASO I”““““” <

:

:

3

1979

1980 Month

Figure 8. Variation in [a] the number of species; [b] diversity [Shannon-Wiener]; ability; and [d] species richness of the surf-zone fish assemblage as indicated with the fine-meshed net.

from

[c] equity catches

consistedof the November 1979sampleand wascharacterized by H. breviceps.The second group was associatedwith samplestaken in February, March, April and July 1980. This was characterized by U. cape&s; l? olivaceum; A. hololepidotus;R. annulatus; D. sargus; L. richardsoni; R. globicepsand L. mormyrus. Examination of projections onto the second principal axis revealed no additional groupings. Figure 11 indicates projections of samplesand speciesonto the first two principal axes as determined by a correspondence analysisof the biomassdata matrix. A total of 43%of the variation in the original data is explained by these two axes. Projection onto the fist axis revealed the presence of two small, discrete groups characterized by H. brevicepsand L. lithognathus respectively. Projections on the secondaxis indicate the presenceof a less

476

T. A. Lasiak

Percentage IO0 I

80 I

I

40 1

20 I

0 1

r

-1

12

sfm~lor~ty

60 I

L I

100

I

I

I

I

I

80

60

40

20

0

Figure 9. Dendrogram resulting from group-average fine net study. Species codes given in Table 4.

clustering

of species taken during

the

discrete third group characterized by samplescollected during the autumn/winter period (April-September 1980). This group comprisedR. annulatus; U. capensis;A. hololepidotus; D. sargus;l? olivaceum; S. salpa and R. globiceps. The total number of species caught was significantly correlated with the average monthly wind speed, direction, photoperiod and sea temperature on the sampling date (0.025
Long-term fluctuations

in a surf-zone fish assemblage

477

that fish populations inhabiting surf environments are limited to relatively few species. Recent findings suggestthat this habitat is occupied by a wide variety of species.Schaefer (1967) and Carlisle et al. (1960), working at Fire Island, New York, and southern California respectively, collected 71 speciesof fish from the surf-zone. In the present study the combined results from the coarse and fine seine hauls revealed a complement of 59 species.The contrary findings on the speciescomplement of surf-exposed beachesreflects differences in sampling technique, length and mesh size of nets used. The studies cited above all utilized short, fine-meshedseine nets which are designedprimarily to catch small fish. A common observation made is that bay, inshore and estuarine fish populations are dominated in abundance by a small number of species.This phenomenon was observed by Warfel and Merriman (1944), Gunter (1958), McFarland (1963), Derickson and Price (1973), Oviatt & Nixon (1973), Warburton (1978), Quinn (1980) and in the present study. The abundant specieswere generally found to be low in the trophic structure. Both Gunter (1958) and McFarland (1963) observed that planktivorous fish predominated in the surf environment at Mustang Island, Texas. On a numerical basisplanktivorous fish predominated at King’s Beach the major representatives being H. breviceps; L. richardsoni; I? olivaceum and M. fulciformis. However, on the basisof biomassthe predominant trophic component alternated between planktivores and benthic feeders (Lasiak, 1983). Only a few workers have applied the criterion ‘ relative ’ abundance to the charac-

----.4r

08

1 *I6

.I0 l3 5;

I A37 51

I I l 22 I

I 1

Figure 10. The first and second principal axes determined by correspondence the surf-zone ichthyofauna assessed during a 13-month study using a tie-meshed The original data matrix was based on numerical abundance. A -months; 0 -

analysis of seine net. species.

478

T. A. Lasiak

I

Figure 11. The first and second principal axes determined by correspondence analysis of the surf-zone ichthyofauna assessed during a 13-month study using a line-meshed seine net. The original data matrix was based on biomass. A - Months; 0 - Species.

terization of dominant species within fish communities (Warfel & Merrimann, 1944; McFarland, 1963; Hillman et al., 1977). This approach gives an indication of positional values which is not influenced by very high numbers of individuals on any one occasion. Comparison of rankings based on ‘total ’ and ‘ relative ’ abundance with that based on frequency of occurrence revealed distinct similarities in the species ranked as dominants. However, the position of one species relative to another was variable. The dominant members of the King’s Beach ichthyofauna were identified as: D. sargus; L. mormyrus; L. richardsoni; I? olivaceum; R. globiceps; R. annulatus and S. salpa. According to McFarland (1963) the primary characteristic of the surf fish populations studied at Mustang Island, Texas was the seasonal changes in abundance. Seasonality in fish abundance has also been reported by Gunter (1958), Springer and McErlean (1962), Norden (1966), Fox & Mock (1968), Oviatt & Nixon (1973), Allen & Horn (1975), Warburton (1978), Saloman & Naughton (1979) and Quinn (1980). The general pattern indicates a decline in both total numbers and species during the winter, with peak abundance being recorded over the spring/summer period. The present study revealed no evidence of seasonality regarding overall abundance or the number of species present. Furthermore, considerable changes in the species composition of the dominant component of the surf-zone ichthyofauna in both long- and short-term were observed. This points to a certain amount of instability in the King’s Beach fish assemblage. However, seasonality may have been masked by abundance cycles of individual species which were not in phase.

Long-term fluctuations

in a surf-zone fish assemblage

479

Diversity is an integrated parameter which has been used widely to assist in the interpretation of temporal patterns in fish assemblages(Bechtel & Copeland, 1970; Dahlberg & Odum, 1970; Oviatt & Nixon, 1973; Stephens et al., 1974; Haedrich & Haedrich, 1974; Allen & Horn, 1975; Livingstone, 1976; Hillman et al., 1977; Warburton, 1978; Quinn, 1980; Ogden & Ebersole, 1981). The Shannon-Wiener index of diversity, fi, has been adopted by the majority of workers. Table 7 comparesthe range and overall values of fi estimated for fish assemblages from a variety of estuarine and coastal environments. To facilitate comparisons, values given in the literature have been transformed to logs to the base 2. The range in values of speciesdiversity measuredin this study was comparable with those from other areas. In fact, King’s Beach appeared to support a greater diversity than most of the other areas. Seasonaltrends in speciesdiversity have been reported by Oviatt and Nixon (1973), Allen and Horn (1975), Livingston (1976) and Hillman et al. (1977). Peak diversity has been observed from spring through to autumn according to study area, lower diversity being consistently measuredin winter. Salomanand Naughton (1979), working in Florida, found speciesdiversity to fluctuate throughout the year. As with the present study, Quinn (1980), working in Queensland, wasunable to discern any regular seasonaltrends in diversity. Relative to fluctuations in numbers of individuals and biomassin the present study, the actual community structure (measuredin terms of diversity) was stable over the longterm asindicated by data from the fine net.

6. Summary of results from multiple regression analysis of dependent biotic parameters b] against independent abiotic parameters [X,] measured during fine net study ;r is the multiple correlation coefficient, r2 is the coefficient of determination, F is F-ratio calculated by analysis of variance, C is the regression coefficient(s))

TABLE

[Yl

Step no.

141

No. species

Average wind speed Direction Photoperiod Sea temperature

0.71 0.76 0.82 0.85

49.9 7.8 9.1 5.3

Log-species

Average wind speed Direction Photoperiod Sea temperature

0.74 0.79 0.83 0.87

55.3 7.2 6.6 6.2

2 3 4

9.95 6.12 5.34 4.49

4.903 3,953 2,237 0.316

;-v-intercept

= Y. 740 I 0,117

12.35 7.49 5.91 5.33

0.111 0.064

0 010 9501

(J -intercept--O No. fish

Wind 48 h

0.64

40.9

6.93

(vPintercepr= Log fish

Wind 48 h

0.62

39-l

452

-963

6.41

0 104

f~ -intercept Mass

Average

wind speed

0 69

47.1

Log-mass

Average

wind speed

0.67

44.2

= 2 436 :

8 91

@---Intercept

=

596

176:

6569

120

-23 422,766

7.93

0.34L

(J-mtercept=Z~092 Dwersity 2 3 4

Direction Average sea temperature Wind 24 h Photoperiod

o-47 0.55 0.57 0.61

22.4 7.8 2-5 4-2 :\a

2 89 1.95 I-30 l-02

intercept

0.78’) O-159 0 065 0 139

=

0 242

480

T. A. Lasiak

Differences have been observed in the relationship of species diversity with its principal components. Allen and Horn (1975), Livingston (1976), Hillman et al. (1977), Warburton (1978) and Winter (1980) observed similar trends in diversity and equitability indices. Quinn (1980) reported a close correlation between species diversity and species richness. In this study with the coarse net both equitability and richness correlated significantly with diversity. Fluctuations were thus due to changes in the number of species and in the distribution of individuals per species. In total, neither distribution nor richness dominated but exceptions did occur; for example in July 1979 and September 1980 large hauls of S. salpa and L. richardsoni resulted in reduced equitability reflected by low diversity. However, the low diversity in March 1980 reflects low species richness. Data from the fine net study showed a more significant relationship between species equitability and diversity than between richness and diversity, which is a widely reported phenomenon. Goodman (1975) criticized the use of the Shannon-Wiener index as having no direct biological meaning, even when measured unambiguously. Precise measurements of diversity are impossible and it is also difficult to correct for the effect of sample size, which is itself influenced by the distribution patterns of individuals relative to the sampling method. Despite its common usage the Shannon-Wiener index has several inadequacies. Diversity is measured in terms of both the number of species and absolute abundance which is not an ideal indicator of importance and has no implications at a functional level. Although the Shannon-Wiener index is relatively independent of sample size, the practicalities of taking random samples must be considered since an increase in sample size from a diverse community invariably includes individuals of the rarer species. This point is of particular relevance to the surf-zone fish assemblage of King’s Beach. Many species are characterized by a high degree of motility, thus it is not possible to delimit the boundaries of these fish assemblages. The apparently random fluctuations in species diversity and wide range of diversity values calculated for King’s Beach indicate a high species turnover. Giligan (1980) suggested that the latter phenomenon typified stressed, variable and irregularly occupied habitats where diversity tended to be regulated by environmental and resource variance. TABLE

various

7. Shannon-Wwxr mdex of diversity estuarine and coastal environments

measured

m fish assemblages

assocrated

Shannon-Wiener

Author

Locatwn

Bechtel & (Zopeland f 1970: Dahlberg & Odum [ 1970) Oviatt & Nixon ,1973 Haedrich & Haedrich ( 1974 I Stephens et al / 1974’ Allen & Horn (1975) Lwingston 1’1976, Hillman et al. I 1977; Saloman & Naughton / 1979’ Wmter !1980, Quinn ‘1980, Ogden & Ebersole I 198 1: Present study ‘coarse net\ Present study (fine net:

Galveston Bay, TX Georgia Estuary Naragansett Bay, RI &Iystic River, MA Los Angeles Harbour, CA Colorado Lagoon, CA Apalachicola Bay, FL Long Island Sound, MA Pinellas Co., FL Swartkops Estuary, S. Africa Serpentme Creek, Queensland Coral Reef, U.S. Virgin Islands King’s Beach, S. Africa King’s Beach, S. Africa

Range

wth

Index

Overall

0.18-I 0 93-2 1.45-3

3U 51 33

O,li-I 0.65-l 0-04-l 0.3G-2

4x 08 59 5-l

O-06-2 0 46-2 0 94-2 0 70-E-61 2 494.01 o-75-3.66 0'56-2

68 7-7 74

70

value

i Sk 3 33

1 71 II tri I 51

3 .!i h i? i 45 I 49

Long-term fluctuations

in a surf-zone fish assemblage

481

The basic definition of a community implies any assemblageof populations in a prescribed habitat or area. This is of doubtful application in the present casewhere the King’s Beach surf-zone is not a distinct habitat. The movement of fish within the Algoa Bay system, of which King’s Beach is a part, is unrestricted. Certain speciesmay accrue advantages from this movement and the fish assemblageis thus not a community in the classicalsense but consistsof groups of specieswith similar needs. The length of time which a particular speciesspendsin the surf-zone is an important facet of the structure of the ‘ community ‘. Results presented indicate the predominance of a smallnumber of specieswhich regularly frequented the King’s Beach surf zone. These were considered to be ‘ resident ’ speciesalthough this did not imply that the sameset of individuals was constantly present in a defined area over a specific time interval. The term ‘ resident ’ actually referred to the presence of a particular speciesfor the duration of the time period, thus allowing for turnover of individuals within a species.The presence together of several species within the study area was clearly demonstrated. However, problems lie in the extent of their recurrence. Classification analysis expressed graphically by dendrogramswas used to demonstrate co-occurring species. Invariably the dominant, frequently occurring species grouped together, and the rarer speciesof sporadic occurrence formed small random groups based on chance occurrence. This is a consequenceof the use of group-average clustering. The failure of classification and correspondence analysis to separate functional groups may also be a reflection of the sampling methods which were unable to differentiate between subhabitats within the surf-zone. The application of correspondence analysis to the data collected did not achieve a simplification of the data matrices as anticipated, possibly as the original data matrix wastoo complex (Clifford & Stephenson, 1975). Reference to the samplegroupings revealed little evidence of temporality, except for projections basedon correspondenceanalysisof the coarsenet data. Hitherto, little use has been made of statistical methods in examining the effects of multiple abiotic parameters on fish assemblages.Notable exceptions are Oviatt and Nixon (1973), Marsh et al. (1978) and Quinn (1980) who all utilized multiple linear regression. Both the coarse and fine net studies revealed significant correlations between the number of species, number of individuals and massof fish caught with various environmental parameters. No significant correlations were obtained using diversity asa biotic parameter. The most noticeable feature to arise from theseanalyseswasthe significanceof wind, either speed or direction, as the primary abiotic variable. In several instanceswind speed over the preceding 12-48 h had a greater influence than average monthly wind speed. This highlighted the need to consider the influences of short-term fluctuations in environmental parameters. Good correlations are by no meansindicative of causation. It may not be wind per se which influences the fish assemblagebut someunmeasuredvariable such as wave action, turbidity or localized temperature changesproduced by upwelling. Warfel and Merriman (1944), working in Connecticut, concluded that fish abundance waspartly conditioned by the degree of turbidity. By reducing the visual acuity of the fish, turbidity may result in larger catches as the fish are less able to detect the fishing gear. The multiple regression model used assumesa linear relationship between dependent and independent variables, a highly unlikely situation in nature. Thus results from multiple regresssionanalysescan only be the basisof speculation on the determinants of change in biotic parameters. Weinstein et al. (1980) concluded that ‘ abiotic variables provide a broad framework of limiting conditions within which biotic interactions act to fine tune community relation-

482

T. A. Las&

ships ‘. Physical environmental parameters determine the quality of the habitat in terms of the water column. In addition they may have an indirect effect by influencing food resource availability, dispersal and immigration rates, visibility in relation to both predation and foraging, etc. In conclusion, it would appear that the continuous gradation of the surf fish assemblage in both time and space casts doubt on the validity of the use and interpretion of community parameters such as species diversity, richness and equitability. Application of these indices to indiscrete communities is mathematically unsound and thus no definite conclusions could be made about temporal fluctuations in the structure of the community. The application of multivariate techniques clearly merits further attention. An intensive approach involving various disciplines is desirable to elucidate the determinants of structure in such fauna1 assemblages.

Acknowledgements The author is indebted to the Department of Environmental Affairs for financial support. Thanks go to Dr L. Underhill of the Department of Mathematical Statistics of the University of Cape Town for carrying out the correspondence analyses. Dr A. McLachlan is thanked for his constructive criticism of the manuscript.

References Allen,

L. G. & Horn, M. H. 1975 Abundance, diversity and seasonality of fishes in Colorado Lagoon, Alamitos Bay, California. Estuarine and Coastal Marine Science 3, 371-380. Bechtel, T. & Copeland, B. 1970 Fish species diversity as indicators of pollution in Galveston Bay, Texas. Contributions to Marine Scieme 15, 103-132. Carlisle Jr, J, G., Schott, J. W. & Abramson, N. J. 1960 The barred surf-perch in southern Califorma. Caltfornm Departmeti of Game and Fisheries Bulletin 109. Chardy, I’., Glenmarec, M. & Laurec, A. 1976 Application of inertia methods to benthic marine ecology: practical implications of the basic options. Esruarine and Coastal Marine Science 4, 179-205. Clifford, H. T. & Stephenson, W. 1975 An Introducrion fo Numerical Clasnjkazion. Academic Press, New York, 229 pp. Dahlberg, M. D. & Odum, E. I’. 1976 AMU~ cycles of species occurrence, abundance and diversity in Georgia estuarine iish populations. American Midland Naturalist 83, 382-392. Derickson, W. K. & Price Jr, K. S. 1973 The fishes of the shore zone of Rehoboth and In&an River Bays, Delaware. Transacn’ons of the American Fisheries Society 102, 552-556. Fager, E. W. 1963 Communities of organisms. In The Sea, Vol. 2 (Hill, M. N., ed.). John Wiley & Sons, New York, pp. 415437. Field, J. G. 1971 A numerical analysis of changes in the soft-bottom fauna along a transect across False Bay, South Africa. Journal of Experimerual Marine Biology and Ecology 7, 215-253. Fox, L. S. & Mock, W. R. 1968 Seasonal occurrence of fishes in two shore habitats in Barataria Bay, Louisiana. Proceedings of the Louisiana Academy of Science 31, 43-53. Giligan, M. R. 1980 Beta diversity of a Gulf of California rocky shore lish community. Envwonmenfai B~ologl of Fishes 5, 109-l 16. Goodman, D. 1975 The theory of diversity-stability relationships in ecology. Quarterl-y Rewew of Bzology 50, 237-266. Gunter, G. 1945 Studies on marine fishes in Texas. Publication of the Institute of Marine Science of rhe Umverst& of Texas 1, l-90. Gunter, G. 1958 Population studies of the shallow water fishes of an outer beach in southern Texas. Publicafton of the Texas Institute of Marine Science 5, 186-193. Haedrich, R. & Haedrich, S. 1974 A seasonal survey of the fishes m the Mystic River, a polluted estuary m downtown Boston, Massachusetts. Estuarine and Coastal Marine Science 2, 59-73. Hillman, R. E., Davis, N. W. & Wennemer, J. 1977 Abundance, diversity and stability in an area of Long Island Sound affected by the thermal discharge of a nuclear power station. Estuarine and Coastal Marine Science 5, 355-381.

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assemblage

483

Lasiak, T. A. 1983 The impact of surf-zone fish communities on fauna1 assemblages associated with sandy beaches. In Sandy Beaches as Ecosystems (Erasmus, T. & McLachlan, A., eds). Junk, The Hague, Netherlands. Livingston, R. J. 1976 Diurnal and seasonal fluctuations of organisms in a north Florida estuary. Esruarine and Coastal Marine Science 4, 373-400. Lloyd, M. & Ghelardi, R. J. 1964 A table for calculating the “equitability” component of species diversity. 3ourml of Animal Ecology 33, 217-255. Malmgren, B., Oviatt, C., Gerber, R. & Jeffries, H. I’. 1978 Correspondence analysis: applications to biological oceanographic data. Estuarine and Coastal Marine Science 6, 429-437. Margalef, R. 1958 Information theory in ecology. General Sysfenratics 3, 36-71. Marsh, B., Crowe, T. M. &Siegfried, W. R. 1978 Species richness and abundance of clinid fish (Teleosti: Clmidae) in intertidal rock pools. Zoologica Afruana 13, 283-291. McFarland, W. N. 1963 Seasonal changes in the numbers and biomass of fishes from the surf at Mustang Island, Texas. Publication of the Texas Institme of Marine Science 9, 91-105. McLachlan, A. 1977 Studies on the psammolittoral meiofauna of Algoa Bay, South Africa I. Physical and chemical evaluation of the beaches. Zoologica Africana 12, 15-32. McLachlan, A. 1979 Volumes of sea water Altered by East Cape sandy beaches. Sourh African 3ournul of SCWZCP 75,75-79. McLachlan, A. 1980 The definition of sandy beaches in relation to exposure: A simple rating system. South African Journal of Science 76, 137-138. Menge, B. A. 1976 Organization of the New England rocky intertidal community: role of predation, competition and environmental heterogeneity. Ecological Monographs 46,355-393. Norden, C. R. 1966 The seasonal distribution of fishes in Vermilion Bay, Louisiana. Wisconszn Academy of Science, Arcs and Letters 5, 119-137. Ogden, J. C. & Ebersole, J. I’. 1981 Scale and community structure of coral reef fishes: A long-term study ot a large artificial reef. Marine Ecology (Progress Series) 4, 97-103. Oviatt, C. A. & Nixon, S. W. 1973 The demersal fish of Narrangansett Bay, an analysis of community structure, distribution and abundance. Estuarine and Coastal Marine Science 1, 361-378. Pearse, A. S., Humm, H. J. & Wharton, G. W. 1942 Ecology of sand beaches at Beaufort, North Carolina. Ecological Monographs 12, 135-190. Pielou, E. C. 1966~ The measurement of diversity in different types of biologicai collections. 3024ral oj Theorerical Biology 13, 131-144. Pielou, E. C. 1966b Shannon’s formula as a measure of specific diversity: Its use and misuse. American Naturalist 100,463465. I’ielou, E. C. 1969 An Inrroductron to Mathematical Ecology. Wiley Interscience, New York, 286 pp. Quinn, N. J, 1980 Analysis of temporal changes in fish assemblages in Serpentine Creek, Queensland. Environmental Biology of Fish 5, 117-133. Reid, G. K. 1955 A summer study of the biology and ecology of East Bay, Texas Part II. TexasJournal of Science 7, 316-343. Reid, G. K. 1956 Observations on the eulittoral ichthyofauna of the Texas Gulf coast. Somhwesr Na~uraltst 1, 157-165. Saloman, C. H. & Naughton, S. I’. 1979 Fishes of the littoral Zone, Pinellas County, Florida. Florida Science 42, 85-93. Schaefer, R. H. 1967 Species composition, size and seasonal abundance of fish in the surf waters of Long Island. New York Fish and Game Journal 1, l-46. Smith, J. L. B. 1965 The Sea Fishes of Southern Africa. Central News Agency, Ltd, South Africa, 580 pp. Springer, V. G. & McErlean, A. J. 1962 Seasonality of fishes on a South Florida shore. Bulletin of Marine Science, Gulf and Caribbean 12,39-60. Sprmger, V. G. & Woodburn, K. D. 1960 An ecological study of the fishes of the Tampa Bay area. Florida State Board for Conservation. Marine Laboratory Proceedings Paper Serial No. 1. Stephens Jr, J. S., Terry, C., Subber, S. & Allen, M. J. 1974 Abundance, distribution, seasonality and productivity of the fish population in Los Angeles harbour 1972-3. In Marine Studies of San Pedro Bay, Part IV, Environmental Field Investigation. pp. l-42. Warburton, K. 1978 Community structure, abundance and diversity of lish in a Mexican coastal lagoon system. Esruarine and Coastal Marine Science 7,497-519. Warfel, H. F. & Merriman, D. 1944 Studies on the marine resources of Southern New England I. An analysis of the fish population of the shore zone. Bulletin of the Bingham Oceanographtc College, Yale Umversity 9, 1-91. Weinstein, M. I’., Weiss, S. L. & Walters, M. F. 1980 Multiple determinants of community structure in shallow marsh habitats, Cape Fear Estuary, North Carolina, USA. Marine Biology 58, 227-243. Winter, I’. E. D. 1980 Studies on the distribution, seasonal abundance and diversity of the Swartkops estuary ichthyofauna. MSc thesis, University of Port Elizabeth, South Africa, 184 pp.