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Structural aspects of the surf-zone fish assemblage at King's Beach, Algoa Bay, South Africa: Short-term fluctuations
Estuarine, Coastal and Shelf Science (1984) l&347-360
Structural Aspects of the Surf-zone Assemblage at King’s Beach, Algoa Africa: Short-term Fluctuations
Fish Bay, South
Theresa Lasiak” Depatiment of Zoology, University of Port Elizabeth, Elizabeth, South Africa 6000
l? 0. Box 1600, Port
Received 18 November 1982 and in revised farm 14 June 1983
fisheries;community; SouthAfrica coast
Keywords:
surf-zone;
variation;
abundance;
diversity;
Short-termchangesin the King’s Beachsurf-zonefish assemblage were investigated by means of two 24 h studies (January and August 1979), and by seine netting on three consecutive days at both high and low tide. They revealed considerable variation in the fish assemblage over a 24 h period. Four species: the gorrie, Pomadasys olivaceum; the mullet, Liza richardsoni; the streepie, Sarpa salpa; and the sand steenbras, Lithognathus mormyrus,dominatedrhe catchesof both 24 h studies. The number of species caught reached a peak just after twilight. Trends in other community parameters were not consistent for these two sets of data. Considerable variation in dominant species, numbers and species diversity indices was observed from day to day as well as between high and low tide. Short-
term fluctuationsin variouscommunityparameters often exceededthe long-term variability observedin a seasonal study of this fishassemblage.
Introduction Little work has been done on short-term temporal fluctuations in fish assemblages,with the exception of those associatedwith coral reefs. Livingston (1976) examinedboth diurnal and seasonalfluctuations in the demersalfish population in North Florida. Quinn and Kojis (1981) studied lunar effects on estuarine fish populations in Queensland.Long-term fluctuations in the surf-zone ichthyofauna at King’s Beach have been describedin another paper (Lasiak, 1984). The present study examines short-term stability of the surf-zone fish assemblageat King’s Beach. The influence of photoperiodicity was investigated during two 24 h studies Tidal influences were studied by netting during both high and low tide. The latter also gave an indication of day to day variability in the fish assemblage.Finally a comparisor is made of short- and long-term fluctuations in the assemblage. Methods To assessthe effect of day/night cycles on the surf-zone fish community at King’s Beach, ‘Present Umtata,
address: Transkei,
Department of Zoology, southern Africa.
University
of Transkei,
Private
Bag X5092,
347 0272-7714/84/030347+14
$03.00/O
0 1984 Academic
Press Inc. (London)
Limb,
’
348
T. Lusiak
24 h studies were carried out in January and August 1979. A description of the netting procedure is given by Lasiak (1984). At 3 h intervals three hauls were made with a beach seine net 60 m long and 2 m deep with a stretched mesh size of 4 cm. On both occasions sampling commenced in the late afternoon and was continued through to give an overlap the following day. Thus nine separate sessions were performed during the course of each 24 h study. In February 1980 an attempt was made to study the influence of tide on the surf-fish community. Three hauls were made on three consecutive evenings during high tide, followed a week later by sampling on three consecutive evenings during low tide. The catch from each seine haul was sorted by species, counted, weighed and measured. Fluctuations in the assemblage were analysed in terms of abundance, biomass and diversity. The ‘total’ and ‘relative’ abundance rankings were estimated for each sampling session as described in Lasiak (1984). As Fager (1963) pointed out, the number of species, number of individuals and biomass, considered as separate entities, do not account for the structure of communities. Species diversity is a community parameter used widely to establish whether, to what extent, and why communities change with time (Pielou, 1974). Species diversity was calculated using the Shannon-Wiener function as modified by Pielou (1966). Species richness and equitability were estimated according to Margalef (1958) and Pielou (1969) respectively.
TABLE 1. Total and relative abundance, fish during a 24 h study at King’s Beach
biomass and frequency in January 1979
Abundance Total Relative Species
Amblyrhynchotes honckenil Argyrosomus hololepidotus Austroglossus pectoralis Caranyx sp. Diplodus sargw Hepsetia breviceps Lithognarhus lithognathus Lithognathus mormyrtu Liza dumeriii Liza richardsoni Liza tricuspidens Monodactylus falciformis Mugil cephalus Myliobatis a&la Natycephalus indicus Pomadasys commersonni Pomadasys olivaceum Pomatomw saltatrix Rhabdosargus globiceps Rhabdosargus holubi Rhinabatos annulatus Sarpa salpa Scomber
japonicus
Sphyraena africana Umbrina cape& Total
of occurrence
of surf-zone
Biomass Total
Relative
Frequency
w
6)
(W
6)
(%)
1.4 0.6 0.1 0.2 0.8 0.2 0.3 5.8 o-5 18.7 0.2 0.8 0.2 0.1
IO.2 2.5 2.2 1.7 5.1 2.5 2.9 3.6 20.3 2.2 0.2 0.2 1.5 26.5 1.8 2.2 9.4 5.1 -
0.6 1.7 0.1 0.1 0.6
0.7 5.9 3.0 0.7 2.2 4.4 3-o 26.7 3.0 5.2 1.5 2.2 3.7 13.3 5.9 0.7 9.6 4.4 3.7 -
77.8 33.3 33.3 44.4 88.9 33.3 44.4 55.6 44.4 88.9 22.2 33.3 33.3 22.2 11.1 11.1 88.9 55.6 11.1 44.4 44.4 66.7 11.1 33.3 22.2
3314
139.7
-
-
-
Structure
of a surf-zone
fish
349
assemblage
TABLE 2. Total and relative abundance, fish during a 24 h study at King’s Beach
biomass and frequency in August 1979 Abundance Total Relative
Species
Amblyrhynchotes honckenii Argyrosomus hololepidotus Cheimerius nufar Dasyatis pastinacus Dtplodus sargus Halaelurus natalensis Heteromycteris capensis Lithognathus lithognathus Lithognathus mormyrus Liza dumerili Ltia richardsoni Liza
tricuspidens
Merluccius capenn’s Monodactylus falctfotmis Mugil cephalus Mustelus sp. My[iobatis aquila Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Raja miraletus Rhabdosargus globiceps Rhabdosargus holubi Rhinobatos annulatus Sardinops ocellata Sarpa salpa Squalus actiipennis Tachysurus feliceps Trdla capensis Umbrina capensis Total
(%)
w
1.3 0.5 0.1 0.7 6.6 0.3 0.7 1.2 4.9 0.1 5.2 0.8 0.3 0.1 0.1 0.3 0.8 0.1 37 1 0.5 0.1 0.3 0.5 1.7 0.1 33.8 0.1 0.1 0.1 1.2
7.1 0.2
757
0.2 16.9 0.4 0.4 3.5 8.2 0.2 8.2 0.4 -0.2 3.2 0.2 17.7 0.2 0.2 0.4 7.5 22.4 0.8 0.8 0.6 124.3
of occurrence
Total w 0.6 1.2
Biomass Relative
of surf-zone
Frequency
of4
w
2.3 0.8 -
44.4 11.1 11.1 22.2 66.7 11.1 44.4 44.4 55.6 11.1 77.8 44.4 11.1 11.1 11.1 11.1 33.3 11.1 66.7 22.2 11.1 11.1 44.4 44.4 11.1 77.8 11.1 11.1 11.1 77.8
7.6 7.6
6.8 2.3 10.6 7.6
1.5 3.0 3.8 2.3 4.6 -
11.4 10.6 2.3 3.0 12.1
-
Results A total of 3314 individuals representing 25 specieswas caught during the 24 h study in January 1979, as compared with 757 fish representing 30 speciescaught in August 1979. The five numerically most abundant speciesaccounted for 93%of the total catch in January. These were: Pomadasysolivaceum; Liza richardsoni; Sarpa salpa; Lithognathus mormyrus and Amblyrhynchotes honckenii (Table 1). In August the five dominant species,accounting for 86.7% of the total catch were: l? olivaceum; S. salpa; Diplodus sargus;Liza richardsoni and Lithognathus mormyrus (Table 2). Thus four of the numerically dominant specieswere common to both study periods. On the basis of relative abundance P. olivaceum was the most predominant speciesin January. However, the contribution of this speciesto the total was reduced from 58.2% to 26.5% (Table 1). Rankings basedon total and relative abundanceindicated similar dominance hierarchies, although there were slight differences in position. Thus D. sargusin January, ranked 7th on the basisof numerical abundance, rose to 5th position on the basis of relative abundance.Relative abundancerankings for August (Table 2) indicated the pre-
350
T. Lasiak
dominance of the same five species as highlighted by total abundance rankings. However, S. salpa replaced P. olivaceum as the most predominant species, accounting for 22.4% of the points allocated. In January 1979, ranking based on total biomass indicated that the five major species accounted for 86% of the total fish biomass. In order of decreasing contribution these species were: Liza richardsoni; P. olivaceum; Rhinobatos annulatus; S. salpa and HT
LT
HT
LT
I
ii
600 1
1’
HT
\ ’
5 =, 4002 200 oICQ-
(b)
SO2 ;
60-
2 g
40-
20 -
Time
(hours)
Figure 1. Fluctuations in (a) the total number of fish; (b) the mass of fish, caught at King’s Beach during a 24 h study in January 1979. HT-High tide; LT-low tide. LT
HT
LT
HT
Tome (hours)
Figure 2. Fluctuations in (a) the total number of fish; (b) the mass of fish, caught at King’s Beach during a 24 h study in August 1979. HT-High tide; LT-Low tide.
Structure
of
a surf-zone fish assemblage
351
Lithognathus mormyrus. In August 1979 the five dominant species, Dasyatis pastinacus; R. annulatus; S. salpa; Lithognathus lithognathus and Liza richardsoni, accounted for 63% of the overall catch. This ranking system emphasized the presence of large fish, consequently the positions of D. pastinacus, R. annulatus and Lithognathus lithognathus were elevated in comparison with the abundance rankings. On the basis of relative biomass the five dominant species caught in the January study were: Liza richardsoni; P. olivaceum; R. annulatus; Argyrosomus hololepidotus and Pomatomus saltatrix. In August the five dominant species were: Umbrina capensis; R. annulatus; S. salpa; Liza richardsoni and D. pastinacus, which together accounted for 52.3% of the points allocated. Whether biomass was expressed on a total or relative basis two species, Liza richardsoni and R. annulatus were consistently dominant. Fluctuations in the numbers and mass of fish caught during the 24 h studies in January and August are shown in Figures 1 and 2 respectively. Two peaks in abundance were apparent in January, both associated with low tide. The smaller peak coincided with twilight and the larger with noon. The catch statistics in Table 3 revealed that P. olivaceum was responsible for both peaks. In the 20.00 hours haul this species accounted for approximately 70% of the catch; at 12.00 hours it accounted for 86.4% of the catch. No clear trends were evident regarding the number of fish caught during the August study (Table 4). The highest number was caught at twilight (17.30 hours), this was followed by a decline with
TABLE
caught
3. Results from the 24 h study at King’s in three consecutive hauls) Time
Species Amblyrhynchotes honckenii Arwosomus hololepidotus Austroglossus pectoralis Caranx sp. Diplodus sargus Hepsetia breviceps Lithognathus firhognathus Lithognathus mormyrus Liza dumerili Liaa richardsoni Liza tricuspidens Monodactylus falczformis Mugil cephalus Myliobatis aquila Platycephalus indicus Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Rhabdosargus globiceps Rhabdosargus holubi Rhinobatos annulatus Sarpa saipa Scomber japonicus Sphyraena africana Umbrina cape&s Total Total
number number
of individuals of species
21.00
24.00
03.00
06.00
3
10 10
8 6
3 3
4
5 5 13 10
2 2
1 2 61 2 9 2
1
1 3 101 4 4
8 1 1 15
1979 (number
(hours)
18.00
2
Beach January
1 2 2 4
09.00
15.00
15
1 4
1 79
12.00
336
18.00 4
1
1
1 2
4
187 1 18
2 2 1 1
1 1
12 2
1 1 15 7 4 6
37 7
17 3
58 3
3
1 3 28
245 1 3 1
3
3
384 17
158 14
80
5 1
3 3 1 2
1531 2
1 12
14 136 12
193 11
195
2 29
14 25
351 8
1773 12
239 5
43 9
of individuals
Total No. of each species 47 19 4 6 26 5 11 192 18 621 6 25 6 3 1 2 1928 18 4 11 11 303 1 42 4 3314 25
352
T. Lasiak
TABLE 4. Results from the 24 h study at King’s caught in three consecutive hauls) Time Species
17.30
Amblyrhynchotes honckenii Argyrosomus hololepidotus Cheimerius nujar Dasyatis pastinacus Dtplodus sargus Halaelurus natalensis Heteromycteris capensis Luhognathus lithognathus Lithognathus mormyrus Liaa dumerili Liza richardsoni Liza tricuspidens Merluccius cape&s Monodactylus jalc@nmis MugiT cephalus Mustelus sp. Myliobatis aquila Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Raja miraletus Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annulatus Sardinops ocellata Sarpa salpa Squalus acutipennis Tachysurus feliceps T&la capensis Umbrina cape&s Total number Total number
of individuals of species
20.30
23.30
4 4 4 7 1 5 7 2 3 2
02.30
Beach August
1979 (number
(hours) 05.30
2
08.30 3
21 2 1 1 19
6
5
1
1
1
1 2 1 1 1
11.30
14.30
17.30
2
3
1
7 1
1 1
26 1
1 1 2 1 113
6 3
1 31
3
4 1 2
126 1
1 2 1 2
1
81
4
1 3 102
60
4
1
1
2
1
1
223 13
57 17
183 12
74 7
143 10
1 7
1
2 1 1
11 6
3
24 8
2
1
4 3
38 8
of individuals
Total No. of each species 11 4 1 5 50 2 5 9 37 1 39 6 2 1 1 2 6 1 281 4 1 2 4 13 1 256 1 1 1 9 757 30
considerable variation during the night. The twilight peak reflected the predominance of P. olivaceum and S. salpa. Two peaks in biomass were recorded during the January study, both occurring just before low tide (Figure 1). A low peak at 21.0&24.00 hours and a prominent peak at 09.00-12.00 hours. The number of individuals and mass of fish caught were not directly correlated. In August, peak biomass was recorded during low tide at 20.30 hours, and thereafter biomass showed a rapid decline (Figure 2). No species was present throughout the entire sampling period. In January D. sargus, Liza richardsoni and P. olivaceum were the most prevalent species, each with a frequency of occurrence of 88.9% (Table 1). The most prevalent species caught during the August study were S. salpa; U. cape& and Liza richardsoni each with a percentage of occurrence of 77.8% (Table 2). Comparison of frequency of occurrence with catch statistics suggests that the fish assemblage could be divided into groups on the basis of their response to the die1 cycle. Of the 22 species recorded in January, 14 were present irrespective of the day/ night cycle, 5 species appeared to be nocturnal and 2 were diurnal. The remaining four
Structure of a surf-zone fish assemblage
353
could not be classified owing to their scarcity. Similarly in August 13 specieswere caught regardlessof light conditions, 2 were nocturnal and the remaining 15 were unclassified. The die1 variation in the total number of speciescaught was similar in January and August (Figures 3 and 4). There was a peak just after twilight, and thereafter a decline with somevariation during daylight. There was no correlation between number of species and tide conditions. In January the greatest diversity was recorded at night; it declined rapidly up to 09.00 hours and remained at a relatively low level throughout the day (Figure 3). The Shannon-Wiener index varied from 0’ 37 to 2 ‘65 during this study period with a mean of 2.06. Two peaks in diversity were apparent in the August study, coinciding with low tide. During this period the Shannon-Wiener index varied from 0.86 to 3.83 with a mean of 2.64. In the January study linear correlation indicated a stronger relationship between equitability and diversity (r = 0.87; P
Time
(hours)
Figure 3. Die1 variation in diversity, equitability, number of species and species richness of the surf-zone fish assemblage during a 24 h study in January 1979. HT-High tide, LT-Low tide.
354
T.
Lasiak
TABLE 5. Summary of catch statistics (number of individuals caught during a study of shortterm variations in the King’s Beach surf-zone fish assemblages as assessed by hauls with a coarse net on three consecutive nights under low- and high-tide conditions)‘, 11/2/1980 Species *Amblyrhynchotes honckenii Anchoviella commersonni Argyrosomus hololepidotus ‘Diplodus sargus Heteromycteris capensis Lithognathus lithognathus *Lithognathus mormyrus Liza dumerili *Liza richardsoni *Liza tricuspidens *Monodactylus falczformis Myliobatis aquila Pagellus natalensis Pomadasys commersonni *Pomadasys olivaceum Pomatomus saltatrix *Rhabdosargus globiceps ‘Rhabdosargus holubi *Rhinobatus annularus *Sarpa salpa ‘Trachurus capensis * Umbrina capensis Total Total
no. of individuals no. of species
121211980
N2
4
1
5
2.5
1
1
0.3
2
2
1.0
4
4
1.3
775 387.5
1 22
23
7.7
4
64 1 8 1
21.3 0.3 2.7 0.3
737 1
38 2
4
NT
i?
131211980
N,
3
1.5
4
2.0
N, % 4
60 1
NT
62 1
1 1
1
1
0.5
1
2
1.0
1
1
0.5
2 6
2 7
E
1.0 3.5
N,
N2
1
16
1
0.3
1
1
1
5 1
0.3 0.7 1.7 0.3
1
0.3
66 11 36 113 6 4 8 13
37.7
112 2 3
2
0.5
8
24
12.0
22
22
11.0
1 3
1 1 5
0.5 0.5 2.5
1
1
0.5
2
2
1.0
7
3.5
64 9
32.0
7 1 749 7
53 802 401 ,O 8 10
27 5
iii 1
1 1
NT
37 6
Sampling on consecutiveevenings A total of 1162 fish representing 22 specieswas caught during the consecutive sampling sessions(Table 5). No specieswere consistently dominant, although Liza richardsoni and Monodactylus falciformti were predominant on five out of six occasions. The sand steenbras, Lithognathus mormyrus, one of the major speciescaught during low tide, was only of minor importance at high tide. Summation of numerical abundancesover the six days indicated that the five dominants were: Lithognathus mormyrus; Liza richardsoni; M. falclformis; D. sargusand l? olivaceum (Table 5). On the basisof relative abundance the major species, in order of decreasing rank, were: Liza richardsoni; M. falctformis; Lithognathus mormyrus; D. sargusand S. salpa. This ranking was not overly influenced by the large haul of Lithognathus mormyrus on the first day, which accounted for 66 ‘7% of the entire catch (Table 5). The lack of consistent dominance was also revealed by the biomassdata (Table 6). On this basis the predominance of l? saltatrix; R. annulatus and U. cape& was increased as a result of the large massof the specimenscaught. Summatedbiomassthroughout the study period revealed that five dominant species,Lithognathusmormyrus; Liza richardsoni; U. capensis;M. falciformis and Lithognathus lithognathus, accounted for 77.7% of the catch (Table 6). Comparisonsof rankings basedon total and relative biomassindicated the same dominant specieswith differences in their positioning and relative contribution. Only one species, P. olivaceum, was caught throughout the study period. Thirteen
Structure of a surf-zone fish assemblage
191211980 N,
N2 1
6 10
2 13 3
E
1
2
0.7
5
5
1.7
3
3
1.0
8 2 25 2 5
1 2 1
2
20/2/1980
N, NT
1 2 3
2.7 8.3 1.7
Nl
N2
N,
1
33 1
11.0 0.3
3
3
1.0
15
19
8.3
1
7
8
2.7
0.3 0.7 1.0
4 1
1
5 1
1.7 0.3
1
0.3
19 4
17 8
55 10
2.3 0.3 1.0 27.3
0.3
18.3
N,
N2
N, NT
2
3
1
1 3
4
1 2
1
7 1 3
7 3
17 8
58 82 6 11
0.7 0.3 0.3 1.7
2
6
2.0
9
5
14
4.7
2 2
3
1
1
6 2 1 2 1 3
2.0 0.7 0.3 0.7 0.3 1.0
1 3 2 12 7
2 1 1 5
E
1
I
3
19 4
i-?
5 28 1
1 1
21/2/1980 NT
2 1
4
355
19 7
15 6
2
0.3
46 13
15.3
Total 11 I 1 49 1 3 825 8 117 6 56 1 2 1 20 5 7 5 11 18 8 6
Total
Relative
w
(W
1.0 0.1 0.1 4.2 0.1 0.3 71.0 0.7 10.1 0.5 4.8 0.1 0.2 0.1 1.7 0.4 0.6 0.4 1.0 1.6 0.7 0.5
3.3
12.3 2.2 15.6 4.4 21.1 18.9
6.7 1.1 3.3 7.8 3.3
Frequency w 83.3 16.7 16.7 83.3 16.7 16.7 66.7 16.7 83.3 33.3 83.3 16.7 33.3 16.7 100.0 50.0 83.3 50.6 83.3 66.7 33.3 50.0
L162 22
=N,-Number of fish in 1st haul; N*-number of fish in 2nd haul; N,-number of fish in 3rd haul; NT total number of fish caught per session; g-mean number of fish caught per session. *Species caught irrespective of tides.
specieswere caught irrespective of tides (indicated by an asterisk in Table 5). Pomatomus saltatrix was caught solely at high tide, whereas Pagellus natalensiswas taken only at low tide. There was considerablevariation in diversity, not only between individual hauls on any given day, but alsobetween the summatedvalues over eachsession(Table 7). The diversity index calculated for individual hauls varied between 0.15 and 2.77, for the summated hauls it varied between 0.31 and 3.16. Diversity, equitability and speciesrichness were highest in samplestaken at high tides. The total number of speciescaught varied from 9 to 13, there being no distinct difference between low and high tide samples. Discussion Warfel and Merriman (1944) pointed out that a major feature of the shore-zone fish assemblageis the fact that it is a constantly changing population. The speciescomposition of the fish was never the same;the predominant speciesvaried in both number and kind. The study of short-term fluctuations at King’s Beach highlighted this phenomenon. Most studies on estuarine and coastal fish assemblages have been designedto investigate spatial and seasonalinfluences. The assumption made was that there was little variation
356
T. Lasiak
I.0 -
iy;-
/\.,
/T.
w
2 0.25 CL? 15E E D IO; x Lo
I
I
I
‘\* I
I
I
I
, II.30
7
I
0 /\ 0
5-,
, 17.30
‘\ , 23.30
9
,.--•\
, , 05.30 Time (hours)
0.
, 17.30
Figure 4. Die1 variation in diversity, equitability, number of species and species richness of the surf-zone fish assemblage during a 24 h study in August 1979. HT-High tide; LT-Low tide.
within seasons.McCleave and Fried (1975) pointed out the lack of knowledge concerning differences in the die1 utilization of various habitats by fish. They caught less fish when seining at night in a tidal cove. The number of speciestaken was similar during the day and night although the composition varied. Certain specieswere found to undergo die1 fluctuations in abundance.Livingston (1976) also noted that somespecieswere caught predominantly or exclusively at night in a North Florida estuary. The King’s Beach studies indicated a peak in number of species caught just after twilight, as was the case with numbers, although, in January 1979, a secondpeak of greater magnitude, which reflected the presenceof a large schoolof I? olivaceum, was recorded at 12.00hours. As in previous studies (McCleave & Fried, 1975; Livingston, 1976), certain species at King’s Beach showed nocturnal habits, particularly A. hololepidotus, M. falcaformis and D. pastinacus. Sampling on consecutive days further highlighted the dynamic nature of the King’s Beach ichthyofauna. Fluctuations were observed, not only with respect to dominant species,but alsowith respect to the number of speciescaught, number of individuals and massof fish. The latter three criteria showed1.4-fold; 26-fold and 4-fold increasesrespectively during the study period. This contrasts with the findings of Quinn and Kojis (1981)
Total
mass
Amblyrhynchotes honchenir Anchoviella commersonni Argyrosomus hololepidotus Diplodus sargus Heteromycteris cape& Ltihognathus lithognathus Ltihognathus mormyrus Liza dumerili Liza richardsoni Liza tricuspidens Monodactylus falcsformis Myliobatis aquila Pagellus natalensis Pomadasys commersonni Pomadasys olivaceum Pomatomus saltanix Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annularus Sarpa salpa Trachurus cape&s Umbrina capensis 10.8
10.8
24551.9
73.3
37.6
35.7
4925.9
29477.8
3292 7 244.5
145.7
145.7
3292.7 244.5
446.7
893.3
893.3
14738.9
1646.4 122.3
5.4
36.7
72.9
151.9
12 123.1
12.3
121,5
303.8
302.1
1.7
24264.1
24.6
24.6
971.7
243.0
41.9
2327.4
201,l
(mass of fish caught)
1 l/2/80
TABLE 6. Summary of catch statistics fish assemblage at King’s Beach”
15891.8
2402 8
146.8 238.5
12211.0 338.5 344.0 210.2
1830.9
187.9 305.7
66.3
1245.4
25.6
from coarse-meshed
2905.7
125.6
9.0
412.7
973.2
1252.4
95.3
37.5
12/2/80
20628.4
2402.8
9.0 334.7 544.2 125.6
66.3
13 184.2 338.5 2002.1 210.2
1278.0
95.3
7.5
seine hauls taken during
6876.1
400.5
1.5 55.8 90.7 20.9
11.1
2197.4 56.4 333.7 35.0
213.0
31.8
12,5
807.1
126.2
9.0
222.5
409.3
40,1
a study of short-term
6770.7
1424.1
4.2
1220.9 121.1
3821.8
165.2
13.4
13/2/80
variability
7577.8
126.2
1424.1
4.2
222.5 1220.9 130.1
3821.8
574.5
13.4
40,l
3788 9
63.1
712.1
2.1
111.3 610.5 65.1
1910.9
287.3
6.7
20.1
in the surf-zone
4
(9)
(9)
BT
B
aB, =Mass
of fish caught
in 1st haul;
2960.4
in 2nd
19 504.3
of fish caught
13 130.0
B, =mass
3413.9
477.1
32.7 1444.2 16.3
32.7 1444.2 6.7
9320.0
9320.0 815.2 4954.9 1828.1
499.9
499.9
1237.1 555.5
116.7
34.7
haul;
6501.4
238.6
16.4 722.1 8.2
407.6 2477.5 914.1
4660
249.9
58.4
(9)
0
B,
B, =mass
627.9
(9)
4720.2
mass
191.7 1867.6 1272.6
82.0
(9)
4
Total
477.1
9.6
623.5 1850.2
(9)
4
19/2/80
2.1 3640.2
6 continued
Amblyrhynchotes honckeni Anchoviella commersonni Argyrosomus hololepidotus Dtplodus sargus Heteromycterii capensis Ltihognathus lithognathus Lithognathus mormyrus Liza dumerili Liza richardsoni Liza tricuspidens Monodactylus falcifornns Myliobatis aquila Pagellus natalensis Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annulatus Sarpa salpa Trachurus capensis Umbrina capensis
Species
Table
4
of fish
3191.4
1982.2
6.9
117.9
86.9 858.6
122.8 16.3
(9)
4
caught
7368.0
712.1
in 3rd
7
haul;
14 829.6
33.3
930.9 5.4
(is)
E
4943
239.7 0.7 1874.1
39.3
36.3 286.2
389.1
1108.2
BT=total
719.0 2.1 5622 2
117.9
108.8 858.6
1167.2
1167.2
21.9
3324
100.0
2792.8 16.3
(9)
BT
2696.8
100.0
2670.0
k9
20/2/80
685.3 107.4
5.0
2.2
515.3
70.9 1.1
4
7400.9
2999.6
276.2
105.3 1449.9
1925.1
378.4
266.4
w
of fish caught;
1387.2
mass
2
B, (8)
B=mean
3131.8
225.6
107.5
1058.5
573.2
696.7 470.3
Cd
4
21/2/80
70.9 1.1 696.7 736.7
B
3973.3
999.9
71.7 483.3 1.7 167.3 228.4 35.8
994.5
489.0
23.6 0.4 232.2 245.6
(9)
mass of fish caught.
11919.9
2999.6
215.0 1449.9 5.0 501.8 685.3 107.4
2983.6
1466.9
(9)
BT
103938.6
508.2 1.1 0.7 4149.3 29.7 9320.0 26198.6 815.2 23234.5 2166.6 10868.0 210.2 368.2 1220.9 626.2 3752.7 45.3 954.4 6423.4 1196.5 128.3 11024.6
(9)
Total mass from all dates
4.0
0.5
w
Total
15.6
10.0 1.1
5.6
1.1 3.3
5.6 10.0 1.1 20.0 3.3 18.9
4.4
W)
Relativemass
Structure of a surf-zone fish assemblage
TABLE 7. Short-term variations in community as illustrated by seine net catches
Date 11 February
1980
359
parameters
for the King’s
Beach ichthyofauna
Haul
Species diversity 03
H, 4 HT
0.15 1.56 0.31
0.06 0.52 0.09
0.63 1.22 0.93
8 10
Equitability
(J)
Species richness (S.R.)
No. of species
12 February
1980
H, f4 f4 HT
0.64 1.62 1.94 2.10
0.25 0.81 0.65 0.57
0.83 0.87 1.35 1.76
6 4 8 13
13 February
1980
HI f4 HT
1.58 1.73 2.23
0.68 0.67 0.70
0.84 0.96 1.33
5 6 9
19 February
1980
H, 4 4 HT
1.58 1.36 2.77 2.57
0.79 0.68 0.92 0.77
0.71 0.71 1.71 1.56
4 4 8 10
20 February
1980
4 ff2 4 HT
1.38 2.65 1.97 2.55
0.87 0.88 0.76 0.74
0.71 1.71 0.85 1.57
3 8 6 11
21 February
1980
4 f4 4 HT
2.63 2.33 2.37 3.16
0.94 0.83 0.92 0.85
1.67 1.41 1.28 2.17
7 7 6 13
haul; Hz--2nd
haul; H,-3rd
‘H,-1st
haul; Hvll
hauls combined.
TABLE 8. Comparison of short- and long-term variability in four community parameters measured during studies of the surf-zone ichthyofauna at King’s Beach, as expressed by coefficients of variation. A coarse-meshed net was used,
Time
interval
24 h, January 1979 24 h, August 1979 3 days high- and low-tide in February 1980 26 months from September 1978 to October 1980
No. of species w
No. of fish w
Mass w
33.9 44.8
149.5 97.2
94.8 81.4
47.1 45.7
15.2
173.0
39.2
45.3
27.6
119.5
91.6
94.4
360
T. Lasiak
who were unable to demonstrate significant differences for any of the individual species abundances,diversity indices or total fish abundancesin relation to the changing level of nocturnal illumination between new and full moon. In the present study the number of speciespresent wasstable over both short- and longterm periods, relative to fluctuations in numbers and massof fish caught. With regard to numbers of individuals, short-term variability often exceeded long-term variability. However, speciesdiversity varied more over the long-term (Table 8). The implicit assumption, madeby various workers, of little within-seasonvariation thus appearedto be invalid when applied to the King’s Beach ichthyofauna. Short-term variability in fish assemblages clearly merits more attention. Problems in the characterization of the King’s Beach ichthyofauna reflect the fact that the surf-zone is a small part of a more extensive shallow-water ecosystem.The apparent dynamic characteristics of the fish assemblageresults from alongshore, onshore and offshore migrations. Biotic and abiotic factors, plus interactions within and between them, all play a role in structuring the surf-fish assemblage.Abiotic factors appear to have the primary influence, with short-term variations in wind conditions being particularly important (Lasiak, 1984). Wind influences the surf-zone and its componentsprimarily through wave action which in turn affects prey availability. Acknowledgements The author is indebted to the Department of Environmental Affairs for financial support and to Dr A. McLachlan for his criticisms of the manuscript. References Fager,
E. W. 1963 Communities of organisms. In The Sea, Vol. 2 (Hill, M. N., ed.). John Wiley and Sons, New York, pp. 415-437. Lasiak, T. A. 1984 Structural aspects of the surf-zone fish assemblage at King’s Beach, Algoa Bay, South Africa: Long-term fluctuations. Esruarine, Coastal and Sherf Science 18 (4), in press. Livingston, R. J. 1976 Diurnal and seasonal fluctuations of organisms in a North Florida estuary. Estuarine and Coastal Marine Science 4, 373-400. Margalef, R. 1958 Information theory in ecology. General Systemarics 3, 36-71. M&leave, J. J. & Fried S. M. 1975 Nighttime catches of fishes in a tidal cove in Montsweag Bay, Wiscasset, Maine. Transactions of the American Fisheries Society 104, 30-34. Quinn, N. J. & Kojis, B. L. 1981 The lack of changes in nocturnal fish assemblages between new and full moon phases in Serpentine Creek, Queensland. Environmental Biology of Fishes 6, 213-218. Pielou, E. C. 1966 The measurement of diversity in different types of biological collections. 3ourn~l of Theoretical L%ology 13, 131-144. Pielou, E. C. 1969 An Introduction to Mathematical Ecology, Wiley Interscience, New York, 286 pp. Pielou, E. C. 1974 Ecological Diversity, Wiley Interscience, New York, 165 pp. Warfel, H. E. & Merriman, D. 1944 Studies on the marine resources of Southern New England I. An analysis of the ftsh populations of the shore zone. Bulletins of the Bingham Ockanographic College, Yale University 9, 1-91.
Structural Aspects of the Surf-zone Assemblage at King’s Beach, Algoa Africa: Short-term Fluctuations
Fish Bay, South
Theresa Lasiak” Depatiment of Zoology, University of Port Elizabeth, Elizabeth, South Africa 6000
l? 0. Box 1600, Port
Received 18 November 1982 and in revised farm 14 June 1983
fisheries;community; SouthAfrica coast
Keywords:
surf-zone;
variation;
abundance;
diversity;
Short-termchangesin the King’s Beachsurf-zonefish assemblage were investigated by means of two 24 h studies (January and August 1979), and by seine netting on three consecutive days at both high and low tide. They revealed considerable variation in the fish assemblage over a 24 h period. Four species: the gorrie, Pomadasys olivaceum; the mullet, Liza richardsoni; the streepie, Sarpa salpa; and the sand steenbras, Lithognathus mormyrus,dominatedrhe catchesof both 24 h studies. The number of species caught reached a peak just after twilight. Trends in other community parameters were not consistent for these two sets of data. Considerable variation in dominant species, numbers and species diversity indices was observed from day to day as well as between high and low tide. Short-
term fluctuationsin variouscommunityparameters often exceededthe long-term variability observedin a seasonal study of this fishassemblage.
Introduction Little work has been done on short-term temporal fluctuations in fish assemblages,with the exception of those associatedwith coral reefs. Livingston (1976) examinedboth diurnal and seasonalfluctuations in the demersalfish population in North Florida. Quinn and Kojis (1981) studied lunar effects on estuarine fish populations in Queensland.Long-term fluctuations in the surf-zone ichthyofauna at King’s Beach have been describedin another paper (Lasiak, 1984). The present study examines short-term stability of the surf-zone fish assemblageat King’s Beach. The influence of photoperiodicity was investigated during two 24 h studies Tidal influences were studied by netting during both high and low tide. The latter also gave an indication of day to day variability in the fish assemblage.Finally a comparisor is made of short- and long-term fluctuations in the assemblage. Methods To assessthe effect of day/night cycles on the surf-zone fish community at King’s Beach, ‘Present Umtata,
address: Transkei,
Department of Zoology, southern Africa.
University
of Transkei,
Private
Bag X5092,
347 0272-7714/84/030347+14
$03.00/O
0 1984 Academic
Press Inc. (London)
Limb,
’
348
T. Lusiak
24 h studies were carried out in January and August 1979. A description of the netting procedure is given by Lasiak (1984). At 3 h intervals three hauls were made with a beach seine net 60 m long and 2 m deep with a stretched mesh size of 4 cm. On both occasions sampling commenced in the late afternoon and was continued through to give an overlap the following day. Thus nine separate sessions were performed during the course of each 24 h study. In February 1980 an attempt was made to study the influence of tide on the surf-fish community. Three hauls were made on three consecutive evenings during high tide, followed a week later by sampling on three consecutive evenings during low tide. The catch from each seine haul was sorted by species, counted, weighed and measured. Fluctuations in the assemblage were analysed in terms of abundance, biomass and diversity. The ‘total’ and ‘relative’ abundance rankings were estimated for each sampling session as described in Lasiak (1984). As Fager (1963) pointed out, the number of species, number of individuals and biomass, considered as separate entities, do not account for the structure of communities. Species diversity is a community parameter used widely to establish whether, to what extent, and why communities change with time (Pielou, 1974). Species diversity was calculated using the Shannon-Wiener function as modified by Pielou (1966). Species richness and equitability were estimated according to Margalef (1958) and Pielou (1969) respectively.
TABLE 1. Total and relative abundance, fish during a 24 h study at King’s Beach
biomass and frequency in January 1979
Abundance Total Relative Species
Amblyrhynchotes honckenil Argyrosomus hololepidotus Austroglossus pectoralis Caranyx sp. Diplodus sargw Hepsetia breviceps Lithognarhus lithognathus Lithognathus mormyrtu Liza dumeriii Liza richardsoni Liza tricuspidens Monodactylus falciformis Mugil cephalus Myliobatis a&la Natycephalus indicus Pomadasys commersonni Pomadasys olivaceum Pomatomw saltatrix Rhabdosargus globiceps Rhabdosargus holubi Rhinabatos annulatus Sarpa salpa Scomber
japonicus
Sphyraena africana Umbrina cape& Total
of occurrence
of surf-zone
Biomass Total
Relative
Frequency
w
6)
(W
6)
(%)
1.4 0.6 0.1 0.2 0.8 0.2 0.3 5.8 o-5 18.7 0.2 0.8 0.2 0.1
IO.2 2.5 2.2 1.7 5.1 2.5 2.9 3.6 20.3 2.2 0.2 0.2 1.5 26.5 1.8 2.2 9.4 5.1 -
0.6 1.7 0.1 0.1 0.6
0.7 5.9 3.0 0.7 2.2 4.4 3-o 26.7 3.0 5.2 1.5 2.2 3.7 13.3 5.9 0.7 9.6 4.4 3.7 -
77.8 33.3 33.3 44.4 88.9 33.3 44.4 55.6 44.4 88.9 22.2 33.3 33.3 22.2 11.1 11.1 88.9 55.6 11.1 44.4 44.4 66.7 11.1 33.3 22.2
3314
139.7
-
-
-
Structure
of a surf-zone
fish
349
assemblage
TABLE 2. Total and relative abundance, fish during a 24 h study at King’s Beach
biomass and frequency in August 1979 Abundance Total Relative
Species
Amblyrhynchotes honckenii Argyrosomus hololepidotus Cheimerius nufar Dasyatis pastinacus Dtplodus sargus Halaelurus natalensis Heteromycteris capensis Lithognathus lithognathus Lithognathus mormyrus Liza dumerili Ltia richardsoni Liza
tricuspidens
Merluccius capenn’s Monodactylus falctfotmis Mugil cephalus Mustelus sp. My[iobatis aquila Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Raja miraletus Rhabdosargus globiceps Rhabdosargus holubi Rhinobatos annulatus Sardinops ocellata Sarpa salpa Squalus actiipennis Tachysurus feliceps Trdla capensis Umbrina capensis Total
(%)
w
1.3 0.5 0.1 0.7 6.6 0.3 0.7 1.2 4.9 0.1 5.2 0.8 0.3 0.1 0.1 0.3 0.8 0.1 37 1 0.5 0.1 0.3 0.5 1.7 0.1 33.8 0.1 0.1 0.1 1.2
7.1 0.2
757
0.2 16.9 0.4 0.4 3.5 8.2 0.2 8.2 0.4 -0.2 3.2 0.2 17.7 0.2 0.2 0.4 7.5 22.4 0.8 0.8 0.6 124.3
of occurrence
Total w 0.6 1.2
Biomass Relative
of surf-zone
Frequency
of4
w
2.3 0.8 -
44.4 11.1 11.1 22.2 66.7 11.1 44.4 44.4 55.6 11.1 77.8 44.4 11.1 11.1 11.1 11.1 33.3 11.1 66.7 22.2 11.1 11.1 44.4 44.4 11.1 77.8 11.1 11.1 11.1 77.8
7.6 7.6
6.8 2.3 10.6 7.6
1.5 3.0 3.8 2.3 4.6 -
11.4 10.6 2.3 3.0 12.1
-
Results A total of 3314 individuals representing 25 specieswas caught during the 24 h study in January 1979, as compared with 757 fish representing 30 speciescaught in August 1979. The five numerically most abundant speciesaccounted for 93%of the total catch in January. These were: Pomadasysolivaceum; Liza richardsoni; Sarpa salpa; Lithognathus mormyrus and Amblyrhynchotes honckenii (Table 1). In August the five dominant species,accounting for 86.7% of the total catch were: l? olivaceum; S. salpa; Diplodus sargus;Liza richardsoni and Lithognathus mormyrus (Table 2). Thus four of the numerically dominant specieswere common to both study periods. On the basis of relative abundance P. olivaceum was the most predominant speciesin January. However, the contribution of this speciesto the total was reduced from 58.2% to 26.5% (Table 1). Rankings basedon total and relative abundanceindicated similar dominance hierarchies, although there were slight differences in position. Thus D. sargusin January, ranked 7th on the basisof numerical abundance, rose to 5th position on the basis of relative abundance.Relative abundancerankings for August (Table 2) indicated the pre-
350
T. Lasiak
dominance of the same five species as highlighted by total abundance rankings. However, S. salpa replaced P. olivaceum as the most predominant species, accounting for 22.4% of the points allocated. In January 1979, ranking based on total biomass indicated that the five major species accounted for 86% of the total fish biomass. In order of decreasing contribution these species were: Liza richardsoni; P. olivaceum; Rhinobatos annulatus; S. salpa and HT
LT
HT
LT
I
ii
600 1
1’
HT
\ ’
5 =, 4002 200 oICQ-
(b)
SO2 ;
60-
2 g
40-
20 -
Time
(hours)
Figure 1. Fluctuations in (a) the total number of fish; (b) the mass of fish, caught at King’s Beach during a 24 h study in January 1979. HT-High tide; LT-low tide. LT
HT
LT
HT
Tome (hours)
Figure 2. Fluctuations in (a) the total number of fish; (b) the mass of fish, caught at King’s Beach during a 24 h study in August 1979. HT-High tide; LT-Low tide.
Structure
of
a surf-zone fish assemblage
351
Lithognathus mormyrus. In August 1979 the five dominant species, Dasyatis pastinacus; R. annulatus; S. salpa; Lithognathus lithognathus and Liza richardsoni, accounted for 63% of the overall catch. This ranking system emphasized the presence of large fish, consequently the positions of D. pastinacus, R. annulatus and Lithognathus lithognathus were elevated in comparison with the abundance rankings. On the basis of relative biomass the five dominant species caught in the January study were: Liza richardsoni; P. olivaceum; R. annulatus; Argyrosomus hololepidotus and Pomatomus saltatrix. In August the five dominant species were: Umbrina capensis; R. annulatus; S. salpa; Liza richardsoni and D. pastinacus, which together accounted for 52.3% of the points allocated. Whether biomass was expressed on a total or relative basis two species, Liza richardsoni and R. annulatus were consistently dominant. Fluctuations in the numbers and mass of fish caught during the 24 h studies in January and August are shown in Figures 1 and 2 respectively. Two peaks in abundance were apparent in January, both associated with low tide. The smaller peak coincided with twilight and the larger with noon. The catch statistics in Table 3 revealed that P. olivaceum was responsible for both peaks. In the 20.00 hours haul this species accounted for approximately 70% of the catch; at 12.00 hours it accounted for 86.4% of the catch. No clear trends were evident regarding the number of fish caught during the August study (Table 4). The highest number was caught at twilight (17.30 hours), this was followed by a decline with
TABLE
caught
3. Results from the 24 h study at King’s in three consecutive hauls) Time
Species Amblyrhynchotes honckenii Arwosomus hololepidotus Austroglossus pectoralis Caranx sp. Diplodus sargus Hepsetia breviceps Lithognathus firhognathus Lithognathus mormyrus Liza dumerili Liaa richardsoni Liza tricuspidens Monodactylus falczformis Mugil cephalus Myliobatis aquila Platycephalus indicus Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Rhabdosargus globiceps Rhabdosargus holubi Rhinobatos annulatus Sarpa saipa Scomber japonicus Sphyraena africana Umbrina cape&s Total Total
number number
of individuals of species
21.00
24.00
03.00
06.00
3
10 10
8 6
3 3
4
5 5 13 10
2 2
1 2 61 2 9 2
1
1 3 101 4 4
8 1 1 15
1979 (number
(hours)
18.00
2
Beach January
1 2 2 4
09.00
15.00
15
1 4
1 79
12.00
336
18.00 4
1
1
1 2
4
187 1 18
2 2 1 1
1 1
12 2
1 1 15 7 4 6
37 7
17 3
58 3
3
1 3 28
245 1 3 1
3
3
384 17
158 14
80
5 1
3 3 1 2
1531 2
1 12
14 136 12
193 11
195
2 29
14 25
351 8
1773 12
239 5
43 9
of individuals
Total No. of each species 47 19 4 6 26 5 11 192 18 621 6 25 6 3 1 2 1928 18 4 11 11 303 1 42 4 3314 25
352
T. Lasiak
TABLE 4. Results from the 24 h study at King’s caught in three consecutive hauls) Time Species
17.30
Amblyrhynchotes honckenii Argyrosomus hololepidotus Cheimerius nujar Dasyatis pastinacus Dtplodus sargus Halaelurus natalensis Heteromycteris capensis Luhognathus lithognathus Lithognathus mormyrus Liaa dumerili Liza richardsoni Liza tricuspidens Merluccius cape&s Monodactylus jalc@nmis MugiT cephalus Mustelus sp. Myliobatis aquila Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Raja miraletus Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annulatus Sardinops ocellata Sarpa salpa Squalus acutipennis Tachysurus feliceps T&la capensis Umbrina cape&s Total number Total number
of individuals of species
20.30
23.30
4 4 4 7 1 5 7 2 3 2
02.30
Beach August
1979 (number
(hours) 05.30
2
08.30 3
21 2 1 1 19
6
5
1
1
1
1 2 1 1 1
11.30
14.30
17.30
2
3
1
7 1
1 1
26 1
1 1 2 1 113
6 3
1 31
3
4 1 2
126 1
1 2 1 2
1
81
4
1 3 102
60
4
1
1
2
1
1
223 13
57 17
183 12
74 7
143 10
1 7
1
2 1 1
11 6
3
24 8
2
1
4 3
38 8
of individuals
Total No. of each species 11 4 1 5 50 2 5 9 37 1 39 6 2 1 1 2 6 1 281 4 1 2 4 13 1 256 1 1 1 9 757 30
considerable variation during the night. The twilight peak reflected the predominance of P. olivaceum and S. salpa. Two peaks in biomass were recorded during the January study, both occurring just before low tide (Figure 1). A low peak at 21.0&24.00 hours and a prominent peak at 09.00-12.00 hours. The number of individuals and mass of fish caught were not directly correlated. In August, peak biomass was recorded during low tide at 20.30 hours, and thereafter biomass showed a rapid decline (Figure 2). No species was present throughout the entire sampling period. In January D. sargus, Liza richardsoni and P. olivaceum were the most prevalent species, each with a frequency of occurrence of 88.9% (Table 1). The most prevalent species caught during the August study were S. salpa; U. cape& and Liza richardsoni each with a percentage of occurrence of 77.8% (Table 2). Comparison of frequency of occurrence with catch statistics suggests that the fish assemblage could be divided into groups on the basis of their response to the die1 cycle. Of the 22 species recorded in January, 14 were present irrespective of the day/ night cycle, 5 species appeared to be nocturnal and 2 were diurnal. The remaining four
Structure of a surf-zone fish assemblage
353
could not be classified owing to their scarcity. Similarly in August 13 specieswere caught regardlessof light conditions, 2 were nocturnal and the remaining 15 were unclassified. The die1 variation in the total number of speciescaught was similar in January and August (Figures 3 and 4). There was a peak just after twilight, and thereafter a decline with somevariation during daylight. There was no correlation between number of species and tide conditions. In January the greatest diversity was recorded at night; it declined rapidly up to 09.00 hours and remained at a relatively low level throughout the day (Figure 3). The Shannon-Wiener index varied from 0’ 37 to 2 ‘65 during this study period with a mean of 2.06. Two peaks in diversity were apparent in the August study, coinciding with low tide. During this period the Shannon-Wiener index varied from 0.86 to 3.83 with a mean of 2.64. In the January study linear correlation indicated a stronger relationship between equitability and diversity (r = 0.87; P
Time
(hours)
Figure 3. Die1 variation in diversity, equitability, number of species and species richness of the surf-zone fish assemblage during a 24 h study in January 1979. HT-High tide, LT-Low tide.
354
T.
Lasiak
TABLE 5. Summary of catch statistics (number of individuals caught during a study of shortterm variations in the King’s Beach surf-zone fish assemblages as assessed by hauls with a coarse net on three consecutive nights under low- and high-tide conditions)‘, 11/2/1980 Species *Amblyrhynchotes honckenii Anchoviella commersonni Argyrosomus hololepidotus ‘Diplodus sargus Heteromycteris capensis Lithognathus lithognathus *Lithognathus mormyrus Liza dumerili *Liza richardsoni *Liza tricuspidens *Monodactylus falczformis Myliobatis aquila Pagellus natalensis Pomadasys commersonni *Pomadasys olivaceum Pomatomus saltatrix *Rhabdosargus globiceps ‘Rhabdosargus holubi *Rhinobatus annularus *Sarpa salpa ‘Trachurus capensis * Umbrina capensis Total Total
no. of individuals no. of species
121211980
N2
4
1
5
2.5
1
1
0.3
2
2
1.0
4
4
1.3
775 387.5
1 22
23
7.7
4
64 1 8 1
21.3 0.3 2.7 0.3
737 1
38 2
4
NT
i?
131211980
N,
3
1.5
4
2.0
N, % 4
60 1
NT
62 1
1 1
1
1
0.5
1
2
1.0
1
1
0.5
2 6
2 7
E
1.0 3.5
N,
N2
1
16
1
0.3
1
1
1
5 1
0.3 0.7 1.7 0.3
1
0.3
66 11 36 113 6 4 8 13
37.7
112 2 3
2
0.5
8
24
12.0
22
22
11.0
1 3
1 1 5
0.5 0.5 2.5
1
1
0.5
2
2
1.0
7
3.5
64 9
32.0
7 1 749 7
53 802 401 ,O 8 10
27 5
iii 1
1 1
NT
37 6
Sampling on consecutiveevenings A total of 1162 fish representing 22 specieswas caught during the consecutive sampling sessions(Table 5). No specieswere consistently dominant, although Liza richardsoni and Monodactylus falciformti were predominant on five out of six occasions. The sand steenbras, Lithognathus mormyrus, one of the major speciescaught during low tide, was only of minor importance at high tide. Summation of numerical abundancesover the six days indicated that the five dominants were: Lithognathus mormyrus; Liza richardsoni; M. falclformis; D. sargusand l? olivaceum (Table 5). On the basisof relative abundance the major species, in order of decreasing rank, were: Liza richardsoni; M. falctformis; Lithognathus mormyrus; D. sargusand S. salpa. This ranking was not overly influenced by the large haul of Lithognathus mormyrus on the first day, which accounted for 66 ‘7% of the entire catch (Table 5). The lack of consistent dominance was also revealed by the biomassdata (Table 6). On this basis the predominance of l? saltatrix; R. annulatus and U. cape& was increased as a result of the large massof the specimenscaught. Summatedbiomassthroughout the study period revealed that five dominant species,Lithognathusmormyrus; Liza richardsoni; U. capensis;M. falciformis and Lithognathus lithognathus, accounted for 77.7% of the catch (Table 6). Comparisonsof rankings basedon total and relative biomassindicated the same dominant specieswith differences in their positioning and relative contribution. Only one species, P. olivaceum, was caught throughout the study period. Thirteen
Structure of a surf-zone fish assemblage
191211980 N,
N2 1
6 10
2 13 3
E
1
2
0.7
5
5
1.7
3
3
1.0
8 2 25 2 5
1 2 1
2
20/2/1980
N, NT
1 2 3
2.7 8.3 1.7
Nl
N2
N,
1
33 1
11.0 0.3
3
3
1.0
15
19
8.3
1
7
8
2.7
0.3 0.7 1.0
4 1
1
5 1
1.7 0.3
1
0.3
19 4
17 8
55 10
2.3 0.3 1.0 27.3
0.3
18.3
N,
N2
N, NT
2
3
1
1 3
4
1 2
1
7 1 3
7 3
17 8
58 82 6 11
0.7 0.3 0.3 1.7
2
6
2.0
9
5
14
4.7
2 2
3
1
1
6 2 1 2 1 3
2.0 0.7 0.3 0.7 0.3 1.0
1 3 2 12 7
2 1 1 5
E
1
I
3
19 4
i-?
5 28 1
1 1
21/2/1980 NT
2 1
4
355
19 7
15 6
2
0.3
46 13
15.3
Total 11 I 1 49 1 3 825 8 117 6 56 1 2 1 20 5 7 5 11 18 8 6
Total
Relative
w
(W
1.0 0.1 0.1 4.2 0.1 0.3 71.0 0.7 10.1 0.5 4.8 0.1 0.2 0.1 1.7 0.4 0.6 0.4 1.0 1.6 0.7 0.5
3.3
12.3 2.2 15.6 4.4 21.1 18.9
6.7 1.1 3.3 7.8 3.3
Frequency w 83.3 16.7 16.7 83.3 16.7 16.7 66.7 16.7 83.3 33.3 83.3 16.7 33.3 16.7 100.0 50.0 83.3 50.6 83.3 66.7 33.3 50.0
L162 22
=N,-Number of fish in 1st haul; N*-number of fish in 2nd haul; N,-number of fish in 3rd haul; NT total number of fish caught per session; g-mean number of fish caught per session. *Species caught irrespective of tides.
specieswere caught irrespective of tides (indicated by an asterisk in Table 5). Pomatomus saltatrix was caught solely at high tide, whereas Pagellus natalensiswas taken only at low tide. There was considerablevariation in diversity, not only between individual hauls on any given day, but alsobetween the summatedvalues over eachsession(Table 7). The diversity index calculated for individual hauls varied between 0.15 and 2.77, for the summated hauls it varied between 0.31 and 3.16. Diversity, equitability and speciesrichness were highest in samplestaken at high tides. The total number of speciescaught varied from 9 to 13, there being no distinct difference between low and high tide samples. Discussion Warfel and Merriman (1944) pointed out that a major feature of the shore-zone fish assemblageis the fact that it is a constantly changing population. The speciescomposition of the fish was never the same;the predominant speciesvaried in both number and kind. The study of short-term fluctuations at King’s Beach highlighted this phenomenon. Most studies on estuarine and coastal fish assemblages have been designedto investigate spatial and seasonalinfluences. The assumption made was that there was little variation
356
T. Lasiak
I.0 -
iy;-
/\.,
/T.
w
2 0.25 CL? 15E E D IO; x Lo
I
I
I
‘\* I
I
I
I
, II.30
7
I
0 /\ 0
5-,
, 17.30
‘\ , 23.30
9
,.--•\
, , 05.30 Time (hours)
0.
, 17.30
Figure 4. Die1 variation in diversity, equitability, number of species and species richness of the surf-zone fish assemblage during a 24 h study in August 1979. HT-High tide; LT-Low tide.
within seasons.McCleave and Fried (1975) pointed out the lack of knowledge concerning differences in the die1 utilization of various habitats by fish. They caught less fish when seining at night in a tidal cove. The number of speciestaken was similar during the day and night although the composition varied. Certain specieswere found to undergo die1 fluctuations in abundance.Livingston (1976) also noted that somespecieswere caught predominantly or exclusively at night in a North Florida estuary. The King’s Beach studies indicated a peak in number of species caught just after twilight, as was the case with numbers, although, in January 1979, a secondpeak of greater magnitude, which reflected the presenceof a large schoolof I? olivaceum, was recorded at 12.00hours. As in previous studies (McCleave & Fried, 1975; Livingston, 1976), certain species at King’s Beach showed nocturnal habits, particularly A. hololepidotus, M. falcaformis and D. pastinacus. Sampling on consecutive days further highlighted the dynamic nature of the King’s Beach ichthyofauna. Fluctuations were observed, not only with respect to dominant species,but alsowith respect to the number of speciescaught, number of individuals and massof fish. The latter three criteria showed1.4-fold; 26-fold and 4-fold increasesrespectively during the study period. This contrasts with the findings of Quinn and Kojis (1981)
Total
mass
Amblyrhynchotes honchenir Anchoviella commersonni Argyrosomus hololepidotus Diplodus sargus Heteromycteris cape& Ltihognathus lithognathus Ltihognathus mormyrus Liza dumerili Liza richardsoni Liza tricuspidens Monodactylus falcsformis Myliobatis aquila Pagellus natalensis Pomadasys commersonni Pomadasys olivaceum Pomatomus saltanix Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annularus Sarpa salpa Trachurus cape&s Umbrina capensis 10.8
10.8
24551.9
73.3
37.6
35.7
4925.9
29477.8
3292 7 244.5
145.7
145.7
3292.7 244.5
446.7
893.3
893.3
14738.9
1646.4 122.3
5.4
36.7
72.9
151.9
12 123.1
12.3
121,5
303.8
302.1
1.7
24264.1
24.6
24.6
971.7
243.0
41.9
2327.4
201,l
(mass of fish caught)
1 l/2/80
TABLE 6. Summary of catch statistics fish assemblage at King’s Beach”
15891.8
2402 8
146.8 238.5
12211.0 338.5 344.0 210.2
1830.9
187.9 305.7
66.3
1245.4
25.6
from coarse-meshed
2905.7
125.6
9.0
412.7
973.2
1252.4
95.3
37.5
12/2/80
20628.4
2402.8
9.0 334.7 544.2 125.6
66.3
13 184.2 338.5 2002.1 210.2
1278.0
95.3
7.5
seine hauls taken during
6876.1
400.5
1.5 55.8 90.7 20.9
11.1
2197.4 56.4 333.7 35.0
213.0
31.8
12,5
807.1
126.2
9.0
222.5
409.3
40,1
a study of short-term
6770.7
1424.1
4.2
1220.9 121.1
3821.8
165.2
13.4
13/2/80
variability
7577.8
126.2
1424.1
4.2
222.5 1220.9 130.1
3821.8
574.5
13.4
40,l
3788 9
63.1
712.1
2.1
111.3 610.5 65.1
1910.9
287.3
6.7
20.1
in the surf-zone
4
(9)
(9)
BT
B
aB, =Mass
of fish caught
in 1st haul;
2960.4
in 2nd
19 504.3
of fish caught
13 130.0
B, =mass
3413.9
477.1
32.7 1444.2 16.3
32.7 1444.2 6.7
9320.0
9320.0 815.2 4954.9 1828.1
499.9
499.9
1237.1 555.5
116.7
34.7
haul;
6501.4
238.6
16.4 722.1 8.2
407.6 2477.5 914.1
4660
249.9
58.4
(9)
0
B,
B, =mass
627.9
(9)
4720.2
mass
191.7 1867.6 1272.6
82.0
(9)
4
Total
477.1
9.6
623.5 1850.2
(9)
4
19/2/80
2.1 3640.2
6 continued
Amblyrhynchotes honckeni Anchoviella commersonni Argyrosomus hololepidotus Dtplodus sargus Heteromycterii capensis Ltihognathus lithognathus Lithognathus mormyrus Liza dumerili Liza richardsoni Liza tricuspidens Monodactylus falcifornns Myliobatis aquila Pagellus natalensis Pomadasys commersonni Pomadasys olivaceum Pomatomus saltatrix Rhabdosargus globiceps Rhabdosargus holubi Rhinobatus annulatus Sarpa salpa Trachurus capensis Umbrina capensis
Species
Table
4
of fish
3191.4
1982.2
6.9
117.9
86.9 858.6
122.8 16.3
(9)
4
caught
7368.0
712.1
in 3rd
7
haul;
14 829.6
33.3
930.9 5.4
(is)
E
4943
239.7 0.7 1874.1
39.3
36.3 286.2
389.1
1108.2
BT=total
719.0 2.1 5622 2
117.9
108.8 858.6
1167.2
1167.2
21.9
3324
100.0
2792.8 16.3
(9)
BT
2696.8
100.0
2670.0
k9
20/2/80
685.3 107.4
5.0
2.2
515.3
70.9 1.1
4
7400.9
2999.6
276.2
105.3 1449.9
1925.1
378.4
266.4
w
of fish caught;
1387.2
mass
2
B, (8)
B=mean
3131.8
225.6
107.5
1058.5
573.2
696.7 470.3
Cd
4
21/2/80
70.9 1.1 696.7 736.7
B
3973.3
999.9
71.7 483.3 1.7 167.3 228.4 35.8
994.5
489.0
23.6 0.4 232.2 245.6
(9)
mass of fish caught.
11919.9
2999.6
215.0 1449.9 5.0 501.8 685.3 107.4
2983.6
1466.9
(9)
BT
103938.6
508.2 1.1 0.7 4149.3 29.7 9320.0 26198.6 815.2 23234.5 2166.6 10868.0 210.2 368.2 1220.9 626.2 3752.7 45.3 954.4 6423.4 1196.5 128.3 11024.6
(9)
Total mass from all dates
4.0
0.5
w
Total
15.6
10.0 1.1
5.6
1.1 3.3
5.6 10.0 1.1 20.0 3.3 18.9
4.4
W)
Relativemass
Structure of a surf-zone fish assemblage
TABLE 7. Short-term variations in community as illustrated by seine net catches
Date 11 February
1980
359
parameters
for the King’s
Beach ichthyofauna
Haul
Species diversity 03
H, 4 HT
0.15 1.56 0.31
0.06 0.52 0.09
0.63 1.22 0.93
8 10
Equitability
(J)
Species richness (S.R.)
No. of species
12 February
1980
H, f4 f4 HT
0.64 1.62 1.94 2.10
0.25 0.81 0.65 0.57
0.83 0.87 1.35 1.76
6 4 8 13
13 February
1980
HI f4 HT
1.58 1.73 2.23
0.68 0.67 0.70
0.84 0.96 1.33
5 6 9
19 February
1980
H, 4 4 HT
1.58 1.36 2.77 2.57
0.79 0.68 0.92 0.77
0.71 0.71 1.71 1.56
4 4 8 10
20 February
1980
4 ff2 4 HT
1.38 2.65 1.97 2.55
0.87 0.88 0.76 0.74
0.71 1.71 0.85 1.57
3 8 6 11
21 February
1980
4 f4 4 HT
2.63 2.33 2.37 3.16
0.94 0.83 0.92 0.85
1.67 1.41 1.28 2.17
7 7 6 13
haul; Hz--2nd
haul; H,-3rd
‘H,-1st
haul; Hvll
hauls combined.
TABLE 8. Comparison of short- and long-term variability in four community parameters measured during studies of the surf-zone ichthyofauna at King’s Beach, as expressed by coefficients of variation. A coarse-meshed net was used,
Time
interval
24 h, January 1979 24 h, August 1979 3 days high- and low-tide in February 1980 26 months from September 1978 to October 1980
No. of species w
No. of fish w
Mass w
33.9 44.8
149.5 97.2
94.8 81.4
47.1 45.7
15.2
173.0
39.2
45.3
27.6
119.5
91.6
94.4
360
T. Lasiak
who were unable to demonstrate significant differences for any of the individual species abundances,diversity indices or total fish abundancesin relation to the changing level of nocturnal illumination between new and full moon. In the present study the number of speciespresent wasstable over both short- and longterm periods, relative to fluctuations in numbers and massof fish caught. With regard to numbers of individuals, short-term variability often exceeded long-term variability. However, speciesdiversity varied more over the long-term (Table 8). The implicit assumption, madeby various workers, of little within-seasonvariation thus appearedto be invalid when applied to the King’s Beach ichthyofauna. Short-term variability in fish assemblages clearly merits more attention. Problems in the characterization of the King’s Beach ichthyofauna reflect the fact that the surf-zone is a small part of a more extensive shallow-water ecosystem.The apparent dynamic characteristics of the fish assemblageresults from alongshore, onshore and offshore migrations. Biotic and abiotic factors, plus interactions within and between them, all play a role in structuring the surf-fish assemblage.Abiotic factors appear to have the primary influence, with short-term variations in wind conditions being particularly important (Lasiak, 1984). Wind influences the surf-zone and its componentsprimarily through wave action which in turn affects prey availability. Acknowledgements The author is indebted to the Department of Environmental Affairs for financial support and to Dr A. McLachlan for his criticisms of the manuscript. References Fager,
E. W. 1963 Communities of organisms. In The Sea, Vol. 2 (Hill, M. N., ed.). John Wiley and Sons, New York, pp. 415-437. Lasiak, T. A. 1984 Structural aspects of the surf-zone fish assemblage at King’s Beach, Algoa Bay, South Africa: Long-term fluctuations. Esruarine, Coastal and Sherf Science 18 (4), in press. Livingston, R. J. 1976 Diurnal and seasonal fluctuations of organisms in a North Florida estuary. Estuarine and Coastal Marine Science 4, 373-400. Margalef, R. 1958 Information theory in ecology. General Systemarics 3, 36-71. M&leave, J. J. & Fried S. M. 1975 Nighttime catches of fishes in a tidal cove in Montsweag Bay, Wiscasset, Maine. Transactions of the American Fisheries Society 104, 30-34. Quinn, N. J. & Kojis, B. L. 1981 The lack of changes in nocturnal fish assemblages between new and full moon phases in Serpentine Creek, Queensland. Environmental Biology of Fishes 6, 213-218. Pielou, E. C. 1966 The measurement of diversity in different types of biological collections. 3ourn~l of Theoretical L%ology 13, 131-144. Pielou, E. C. 1969 An Introduction to Mathematical Ecology, Wiley Interscience, New York, 286 pp. Pielou, E. C. 1974 Ecological Diversity, Wiley Interscience, New York, 165 pp. Warfel, H. E. & Merriman, D. 1944 Studies on the marine resources of Southern New England I. An analysis of the ftsh populations of the shore zone. Bulletins of the Bingham Ockanographic College, Yale University 9, 1-91.