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Production ecology of two Caribbean marine ecosystems
Estuarine
and Coastal
Marine
Science
(1973),
I, 303-318
Production Ecology of Two Caribbean Marine Ecosystems I. Physical
Environment
and Fauna
R. R. C. Edwards” Institute
Oceanografico,
Received
2
July
Universidad
de Oriente,
Cumand,
Venezuela
197.3
A quantitative study was made of the invertebrate macrofauna and fish fauna of two shallow water ecosystems. One was in an inlet on a clean sand bottom (I) while the other was on a muddy bottom (2) near a discharge point for domestic effluent. The largest average biomass of littoral infauna of 2.894 g/m* dry flesh weight was found at (2) while the largest average biomass of sublittoral infauna of 5.839 g/m* was found at (I). Fish biomass was 5.048 g/m= at (I) and 1-200 g/m* at (2) suggesting an avoidance reaction to the contaminated water at the latter locality. Diets of demersal fish were predominantly benthic infauna at (I) and epifauna at (2), the latter being related to the presence of a prolific weed fauna in the sublittoral.
Introduction This paper gives basic information collected as part of an ecological energetics study of coastal marine ecosystems in Venezuela. Fukuoka (1965) and Griffiths & Simpson (1972) showed that the region was subjected to seasonal upwelling and high values of primary production obtained by Curl (1959) and Hammer (1967) may be taken as further evidence of enrichment of the coastal waters. Relatively little is known of the marine fauna in this locality although Rodriguez (1969) made some taxonomic and intertidal studies on Margarita Island. Two beaches near Cumanl were chosen for the study (Figure I), one situated near the city and receiving domestic efBuent and the other situated 20 km to the west in a protected inlet.
Methods Intertidal and sublittoral infaunas were sampled with o-25 ms quadrats along continuous transects. Sublittoral samples were taken with SCUBA by transferring bottom deposits to a submerged container. The deposits were passed through a sieve of 1*4-mm mesh size at the surface and the sample preserved in 10% formaldehyde. Epibenthos was sampled by randomly placed 0.25 m2 quadrats on the sea bed, or by measuring squares 3 m x 3 m with a graduated cord. Animals on the surface of the deposit “Present address: Dept. Isle of Man, U.K.
of Marine
303
Biology,
University
of Liverpool,
Port Erin,
R. R. C. Edwards
304
were counted and identified and burrowing forms (e.g. holothurians) were uncovered by probing the bottom. Samples were removed for further study and preserved. Fish populations were sampled with a beach seine net of 25-m length and 3-m depth with a stretched mesh of 1.5 cm in the wings and 0.5 cm in the bag. Each haul was made from a distance of 70 m from the shore and covered an area of approximately 800 m2. Occasional samples of pelagic fish were obtained with rotenone poison. Dry flesh weights were obtained by removing stomach contents and hard parts, such as shells. In the case of echinoderms containing calcareous skeletal material, flesh weights were obtained by rapid combustion at 500 “C for 30 min. Prolonged combustion was avoided since it may lead to errors as a result of decomposition of the skeletal material. Caloric
40’
64OOO’
30’
30’
CAR/SBEAN
SEA
GULF
OF
CAR/AC
Venezuela 100 00’
Figure
r. Location
of sampling area on coast adjacent to Cumani.
Two Caribbean marine ecosystems. I
305
contents were calculated from analyses of protein, lipid and carbohydrate using methods described by Edwards et al. (1969). Physical
environment
San Luis This beach was 5 km in length and lay in a north east/south west direction in front of a suburb of the city. About half way along there was an opening into a small lagoon system. The beach received moderate wave action created by the north east trade winds. This produced a current running in a south west direction along the beach, which dispersed domestic effluent from a discharge point at the north east end. The profile given in Figure z shows that the depth increase was relatively gradual and the littoral zone was about 7 m in horizontal extent. Analyses of particle sizes of the beach and the bottom at 1-m depth are shown in Figure 3. Below 2 m the bottom sediment was anaerobic mud. Sorting coefficients were calculated from the expression z2/Q3/Q1 where Qi and Qa were the first and third quartiles of the cumulative curve. For the beach and sublittoral these were 1.46 and 1.91 suggesting that the former was better sorted than the latter.
70-
\
.
9IO-
\ I 0
I
II 10
I 20
I
I 30
I
Distance
I 40
I
I 50
II
11 60
. 1
70
1 80
Cm)
Figure 2. Depth profiles of Las Ma&as and San Luis beaches. (C.D. =chart -O-O-, San Luis; -@-@-, Las Maritas.
datum).
Las Maritas This beach was situated just inside the inlet Bahia de Mochima which faced north into the Caribbean about 20 km to the west of Cumanb. Its hydrography and physical characteristics were described by Okuda et al. (1968). Th e b each lay on the east side of the inlet and was protected from the prevailing winds with the result that wave action was slight. It was about 200 m in length and 12 m in extent with a rocky shore on either side which extended for a short distance into the sublittoral. The sublittoral profile of Las Maritas (Figure 2) is steeper than San Luis. Particle size analysis of the beach and sublittoral sand are shown in Figure 3. Sorting coefficients for the beach, 4 m and II m depth, were 1.22, 1.73 and 1.50, respectively.
306
R. R. C. Edzcards
Temperature, salinity and dissolved oxygen in the water in Mochima were measured by Okuda et al. (1968). The annual temperature range at depths less than 5 m was 22 to 29 “C, with the lowest temperatures in the upwelling period between December and April. For most of the year the surface water temperature was between 25 and 27 “C. Dissolved oxygen levels in the water varied with the time of day but were usually between 5.5 and 7.0 mg/l. Salinities were in the range 36.5 to 37.0%~ with very slight annual variation. Secchi disc readings at Las Maritas were normally between 15 and 20 m but during the period of upwelling and plankton blooms they were often reduced to 6 to IO m. At San Luis where there were quantities of suspended material in the water readings were 2 to 3 m.
80 !
5 60 ” &I a 40 i cn g 20
Particle
sze
(pm)
Figure 3. Cumulative curves of sand particle size. (a) Las Maritas: -tt, Beach mid-tide level; -O-O-, sublittoral 4-m depth; -V-V-, sublittoral 11-m depth. (b) San Luis: -@-a-, beach mid-tide level; -O-O-, sublittoral 1-m depth. Detritus contents
In Las Maritas at 4-m depth the combustible detritus content of the sand to a depth of IO cm was 158 g dry wt/m2 and at II m depth 117 g. In San Luis at 2 m depth the content was very high at 2192 g/m2, suggesting that deposition on this beach was exceeding breakdown of the sedimentary material by biological action. Chlorophyll
a measurements
These were made following Strickland & Parsons (1968). The quantity of chlorophyll a in the surface I m of sand at 4 m in Las Maritas was 35.4 mg/m2 in the bare sand areas and 114.4 mg in the Enteromorpha zone. At 11-m depth where there were no macroalgae the chlorophyll a content was 25.5 mg/m2. In San Luis beach 21.0 mg/m2 was measured, but this did not include the macroalgae. Bunt et al. (1972) gave estimates of 20-200 mg/m2 with a mean of 69 mg/m2 for shallow water Caribbean deposits. The mean value for Las Maritas of 75 mg/m2 compares closely with this figure. The macrobenthos
The results of the littoral and sublittoral surveys of both beaches are given as biomass and numbers in Tables I, 2 and 3, and depth distribution in Las Maritas is shown in Figure 4. A fauna1 list is given in Appendix Table AI.
Two Caribbean marine ecosystems. I
307
The littoral fauna Las Maritas. The littoral fauna on this beach was dominated by the bivalve mollusc Heterodonax which inhabited a zone at and above mid-tide level. The biomass of the fauna was highest at mid-tide level where the density of this bivalve was greatest. The isopod Excirolana
was the dominant crustacean and occurred throughout the littoral zone. Scolelepis was the dominant polychaete and Amphioxus was present on the lowest part of the beach. The ghost crab Ocypode was found just above the high water mark with a density of about 3 and a dry flesh weight of 1.8 g per metre of shore line. A mean biomass figure for the beach fauna was I ‘079 g dry wt/ms. San Luis. The dominant member of the fauna was Donax denticulatus, which was a typical inhabitant of exposed beaches in this region. The smaller individuals lived highest on the beach (Wade, 1967), the maximum density being at 0.75 m above low water. The dominant crustacean between low water and mid-tide was Emerita holthuisi while the isopod Excirolana occurred above mid-tide level. The dominant polychaete was Scolelepis. Ocypode had a density of 0.2 and a dry flesh weight of 0.13 g per metre of shore line. A mean biomass figure for the beach fauna was 2.894 g dry wt/m2.
23456-
12 13 14 15 16 -
I I
Scale
5&e-%0
Figure 4. Depth distribution of predominant macrofauna in Las Maritas. Scale indicates numbers of individuals per m2 before correction for sampling errors. (C.D.=chart datum.)
Comparison of the beaches
The absence of Donax in Las Maritas may relate to the very slight wave action, which did not permit the normal wave-dependent migratory behaviour (Trueman, 1971). Heterodonax did not show this behaviour and was adapted to sheltered beaches. The filter-feeding
R. R. C. Edwards
Emerita was more common in San Luis where the water contained suspended material. The total biomass (excluding Ocypode) per metre transect in Las Maritas was 12.95 g and in San Luis zo*16 g but if Ocypode was included became 14.70 g and 20.29 g, respectively, Ansell, et al. (1972) found maximum biomasses on Indian beaches 2 to 3 times those in San Luis. Sublittoral infauna Owing to the method of sampling in which deposit was removed with a scoop, some members of the infauna, particularly crustaceans, escaped. To correct for this, a series of 48 cores were taken at 5-m depth in Las Maritas and the macrofauna was pooled and weighed. It was calculated that 0.41 of the benthic biomass was lost with the scoop method due to sampling and sieving errors. Las Maritas. The biomass of the fauna increased from I m to 5 m depth (Table 2) and thereafter declined. At depths below 12 m, which was about the depth of the thermocline, the biomass of infauna was low and some species showed a marked decline in numbers or a discontinuity of distribution (Figure 4). TABLE I. Biomass as g dry flesh wt and numbers beaches Las Maritas
0.75 m
1-0 m
Bivalvia Gastropoda Crustacea Polychaeta Cephalochorda Total
No.
Dry wt
No.
-
-
-
16
0.016
-
16
0.016
12 64 36
II2
Dry wt
per m2 of littoral
Metres above C.D. 0.50 m No.
Dry wt
0.296
332
6.653
-
-
-
64
0.028 0’012
0,040 0.090
fauna on both
0.25 m
No. 92 48
Drywt
0.0 m No.
-
-
-
0.007
464
0’252
-
-
-!
-
-
-
0.336
397
6.783
140
0.259
Dry wt
4
0.003 0’095 -
4 472
0’003 0’101
San Luis 1.0 m No. Bivalvia Crustacea Polychaeta Total
Dry wt
No.
Dry wt
No.
-
-
296
0.264
1564 84 72 1720
2.640 0’297 0.067 3.004
1116 I92 52 1360
-
-
296
0.264
0.25 m
0.50 m
0.75 m
Drywt 3.814 3.336 0.073 7’223
No.
Dry wt
14.4
3.716 0.004 0.146 3.866
4 116 264
0.0 m No. 92 92
Dry wt 0.115 0.115
The sublittoral biomass was dominated by polychaetes followed by molluscs, gastropods, cephalochordates (Amphioxzcs), sipunculids, crustaceans and scaphopods, in that order. A corrected mean figure for sublittoral biomass to a depth of 16 m was 5.839 g/m2. San Luis. The slope of this beach (Figure 2) was less than Las Maritas and thus fewer sublittoral stations were sampled. When correction was made for loss of sublittoral infauna due to sampling errors, the biomass of the beach and the sublittoral was about the same. A corrected mean figure for the sublittoral biomass was 3.247 g/m2. The dominant member of the infauna by weight was the polychaete Diopatra followed by the gastropod Olivella minuta. The infauna was less diverse than in Las Maritas (Appendix Table AI) which may result from the anaerobic bottom conditions.
Two Caribbean marine ecosystems. I
309
One of the few quantitative studies of the fauna in the immediate sublittoral of sandy beaches is that of McIntyre & Eleftheriou (1968) in Scotland. Their mean littoral biomass estimates corresponded with those in Las Maritas while their sublittoral estimates were approximately half those of the latter beach. Sublittoral
epibenthos
In Table 4 are given the mean numbers and dry flesh weights of the epifauna to a depth of IO m. The animals in this Table were those of common occurrence and some species, e.g. holothurians, the decapod Calappa and the hoplocaridan Squilla, are not included. The epifauna were generally of larger body size than the infauna and their distribution was not closely related to depth. Members of the epifauna were sparse between low water and I m although it was in this zone that Squilla was found. This had a density of 0.26 per metre of shore line and a flesh dry weight of 0.97 g.
Las Maritas.
TABLE
2. Biomass as g dry flesh wt and numbers
per ma of sublittoral
infauna in Las Maritas
Metres below C.D. Dry :tm Polychaeta Bivalvia Gastropoda Scaphopoda Crustacea Ophiuroidea Sipunculoidea Cephalochorda Others Total
0’21 I
0.063 0.572 -
0’202
I ‘072
8m Dry wt Polychaeta Bivalvia Gastropoda Scaphopoda Crustacea Ophiuroidea Sipunculoidea Cephalochorda Others Total
No.
3.343 0’779 0.024 0.024
0.650 0.513 0.017
-
684 172 40
0,007
16
0’051 0.123 0,019
72
88 -
0’012
4.693
12 16
16 468
0.432 -
No.
Dry wt
1.812
Dry :tm
No.
Dry wt
No.
3’270 0.876
1404
3’388
1580
0.007 0.035
856 2.195 228 68 32 7i 120
8 2
I394
256 1.894
0’120
72 if 48 204
0.261
0.621 0'012
0.030 0.180
2078
0’752 0.473 0.076 7.426
Dry wt
No.
Dry wt I .626 0.126 0'010
36 I:048
0.434 0.322 0.080 5’405
No. 1492
10 m
0.016
0.064 0.349 0.082
5m
No.
284 44 36
0.024 -
2m Dry wt
16 2
12 m
0.410 0.061 0.116
-
0.895
428 112
128
108 100
-
0.039 0.098 0.391 -
-
44
0’001 0.071
3’310
2192
2'012
4 112
2.609
48
4 4 16
0’003 0.060 0.034 0.070
-
-
820
I’929
Dry w:”
1520
564 64
1.641 0.716
364
16
0.036
48 I44
96 68 204 48
108
0’101
2650
0.280 0.342 o-194 0.260 6.179
No.
Dry wt
IO
16
176 28
2.813 0.614
720 I32
1'593 0.016
20
48 36 4 104 36
24
52 93
0.085 -
-
2405
5.381
1108
No.
Dry wt
No.
0.861 0*0x8 0’010 0’002
3.52 40
0.671 0.128
276 44
12
0,043
12
0’002
0.072
100 16
8 96 36
-
0’010 0’002 0’022 -
688
1.087
12
56
0.055 0’102 0.103
4
4 4 532
0.024 o-39 0.018
0’92.5
The starfishes Astropecten and Luidia remained buried in the sand during the day and emerged at dusk. The gastropods Oliva and COWSshowed burrowing behaviour, whereas Strombina was normally found only on the surface of the sand. Eleftheriou (personal communication) found that starfish and hermit crabs were the dominant
epifauna
in the sublittoral
of a sandy
beach
in Scotland.
estimates were about 0.17 of those observed in Las Maritas.
His
12
16 m
15 m
448
No.
I
14m
256 0.327 156 0.595
0.084 0.038 0’001
6m Dry wt No.
starfish
biomass
-
8
480
310
R. R. C. Edwards
San Luis. Most of the epifauna on this beach was associated with the macroalgae Enteromorpha, Ulva and Ectocarpus, and was composed of small crustacea and molluscs. The blue crab Callinectes was sampled from seine net hauls but its burrowing behaviour may have resulted in underestimates. The epifauna of occasional occurrence, for example Mellita, Callapa, Oreaster and Octopus, were not included in biomass estimates.
The abundant meio- and microfauna of the weed, including harpacticoid copepods, nematodes, turbellarians, ciliates and protozoans were not estimated since in total biomass the meio- and microfauna is small (Hargrave, 1969). TABLE 3. Biomass as g dry flesh wt and numbers per m2 of sublittoral San Luis
infauna in
Metres below C.D. Dry km
No.
1.187
356 62 104
Polychaeta Bivalvia Gastropoda Scaphopoda Crustacea Nemertini Coelenterata Sipunculoidea Ophiuroidea
0’020
Total
1.854
0’133
0’313 0.051 0.084 0.066 -
Dry :tmNo. I 228 0.075 0.650
268 26
334 4 48
0’021
I2 120 I
-
Dry :tmNo.
0,025 0.230 0.162
2
0’012
2
0.016
6572
2.419
69;
0.749 0.015 0.446 0.007 0’01 I 0.167 0.028 0.028 -
404 4 180
I.451
692
62” I 2
37 -
TABLE 4. The biomass and numbers per m2 of the predominant
Conus
Coelenterata
Pettochirus Oliwa Strombina Total
epifauna
San Luis
Las Maritas
Astropecten Luidia
benthic
Dry flesh wt (g)
No.
0’440 0’330 0.042 0’033 0.03 I 0.030 0.008 0.914
0.08 0.03 0.82 0.09 3’70 0.09 0.25 5.06
Dry flesh wt (g)
Alabina
No. 3600
MuSCUlUS
0.780 0.058 0.036 0’030 0.007 0.006
Total
0.917
5059’01
Amphipoda Mysidacea
Calliflectes Diopatra
1000
243 0’010
27 189
Comparing the two beaches it can be seen that the biomass of epifauna was the same but the epifauna in San Luis consisted of a large number of small animals associated with the weed whereas that in Las Maritas consisted of a small number of larger animals. This difference may be related to the food supply of the epibenthos being mainly plant material in San Luis and benthic infauna in Las Maritas. Caloric contents of the macrobenthos were calculated from values given by Brawn et al. (1968) and used in Edwards (1973). Trophic relationships of the macrobenthos
Examinations of stomach contents were made on a qualitative basis only, 23 species representative of all phyla having been examined. The majority of the sublittoral infauna from
Two Caribbean marine ecosystems. I
311
both beaches appeared to be detrital feeders and the stomach contents were almost indistinguishable from detritus samples taken from the corresponding sediments. The most commonly identifiable contents were diatoms, foraminifera, fragments of crustaceans and a amorphous organic material which may have been faecal in origin. In the epifauna Astropecten, Luidia and Calh’nectes were observed to be predators on epiand infauna. Callinectes consumed the gastropod Olivella, polychaetes and bivalves. Astropecten consumed bivalve molluscs (mostly Pitar) gastropods and polychaetes while Luidia consumed polychaetes and small ophiuroids. Christensen (1970) concluded that Astropecten irregularis was a selective predator on bivalves, preferring juveniles or species with low resistance to anoxia, which were more rapidly digested. Since Pitar was uncommon in the benthos its preferential selection by Astropecten could be explained in this way. In the littoral fauna Donax, Heterodonax, Emerita and Scolelepis consumed planktonic diatoms and detrital material while Excirolana consumed crustacean larvae. Fish populations
The majority of the fishes caught on both beaches were migratory types and were probably in continual motion between different beaches along the coast. They were categorized according to their feeding habits: (I) plankton feeders, e.g. Jenhinsia; (2) fish carnivores (i.e. consumers of other fish), e.g. Strongylura; (3) benthos feeders, e.g. Eucinostomus; (4) herbivores, e.g. Mugil. Because the juveniles of many of the demersal fishes feed planktonically, separation into these categories is somewhat artificial but provides a basis for food chain analysis. There were at least 31 species in Las Maritas and 32 in San Luis (Appendix Table Aa). Biomass and numbers
The results of the beach seine net surveys on both beaches are given in Table 5 and are expressed as biomass in Figure 3. In San Luis the net sampled the entire water column but only the lower 3 m in Las Maritas which may have resulted in under-estimates of the planktonic fishes. In view of this, biomass estimates of these fish were calculated from catches TABLE 5. Mean numbers June 1972
of fish per net haul during
Dec./Feb.
Mar./May
the period
June/Aug.
Nov.
Sept./Nov.
Las Maritas No. hauls Plankton feeders Fish carnivores Benthos feeders Herbivores Total
7 277 5 24 5 361
4 9r 2
44 2
139
5 1984 36 rr4 4 2138
5 r4g r7 29 17 211
San Luis No. hauls Plankton feeders Fish carnivores Benthos feeders Herbivores Total
II
78
4 8
I
IO
20
25 I
100
I 44
7 32 30 45 7 II4
3
165 8: 20 279
1970 to
312
R. R. C. Edwards
made on two occasions in Las Maritas when the shoals were observed close to the shore. Opistognathus and Chaenopsiswhich inhabited burrows were not sampled by the net. These together with Gobionellus, which was not captured by the net, were estimated by underwater counts. In order to correct for the efficiency of the net a number of the abundant Haemulon aurolineatum were marked with pelvic fin clips, released into the water as the net approached the shore, and the number recovered in the subsequent haul was counted. During two tests a total of 70 fish were released and 37 were recovered. The method was only approximate since the fish were stressed by previous capture and handling but it gave a measure of the extent of the escapage at the water’s edge where losses occurred below the ground rope. When planktonic fish were excluded from Table 6 the numbers taken in Las Maritas were highest in June/August and lowest in December/February while in San Luis they were highest in September/November and lowest in March/May.
Figure 5. Biomass of fish fauna before correction for gear efficiency. n , Plankton consumers; E, benthos consumers; 1111, fish carnivores; \\\ , herbivores.
Figure 5 shows that total fish biomass in Las Maritas was four times that in San Luis. Part of this difference may relate to differences in food supply for each trophic grouping which, except for the herbivores, was lower in San Luis but part may also be attributed to an avoidance reaction to the contaminated water on the latter beach. In correcting for gear efficiency the dry weights in Figure 5 should be doubled to obtain an approximate estimate of true biomass. The figures for Las Maritas agree closely with those of Hellier (1958) for shallow bays in Texas. Hobson (1973) observed that the numbers of fishes on sandy bottoms at night increased as a result of emergence of fish from adjacent coral areas but the effect of this was probably small in Las Maritas since nearby coral colonies were poorly developed. About 0.6 of the demersal fish biomass in Las Maritas was attributed to fish of small body size, particularly Chaenopsis and Gobionellus, a factor important in energetics studies since these fish have proportionally high metabolic rates. Length/weight relationships and caloriJic contents Length and dry weight relationships are given in Table 6, being analysed in the form W= aX* after logarithmic transformation. Strongylura gave exceptional values which were attributed to the excessive jaw length (25% of standard length) resulting in high values of standard length.
Two Caribbean
marine ecosystems. I
313
Caloric contents were calculated from analysis of protein, lipid and carbohydrate and results of analyses of seven species are given in Table 7. The calorific contents lay in the range 4.59 to 5.14 kcal/g dry wt with a mean of 4.83 when calculated from accepted conversions. TABLE 6. Length/dry
H. aurolineatum H. steindachneri H. boschmae Orthopristis Eucinostomus Umbrina Mugil Nicholsina Oligoplites Strongylura Sphyraena Anchoa (immature) Anchoa (mature) Anchoviella Harengula Jenkinsia
TABLE
7. Biochemical
weight
of fish expressed in the form W= aX* No. specimens
a
b
0~0023 0.0038
64 46 74
0.0041
3.4396 3’2577 3’3215 3.1811
0’0025 0’004.4
3.4236 3.0986
132 62
0.0042 0.0038
3.1181
100
0.0028
58
84 66
3’1771 3.0183 I .8608 3.1316 3’3000 2.9830
45 58 69 49
0.0046
3.1558 3.1627
:i
O’ooIg
3.3632
91
0.0028 0.0217 0'0012
0’0013 0.0039
0’0020
analyses and caloric content
Protein H. aurolineatum H. boschmae Eucinostomus Mugil Oligoplites Strongylura Sardinella
relationships
67.51 66.17 73’24 71.80 68.78 80.13 70’14
of homogenized
mg/~oo mg dry wt Carbohydrate Lipid 0’59 0.48 0.53 0.74 0’53 0.71 0.48
Ash
9.36 8.83 10'00
22.73 23.65 15’95
7’42 6.90 5’40 7.46
23’71 13’94 21.63
20’00
fish
kcal/g dry wt 4.762 4.631 5’147 4.829 4.598
5’110 4’727
Trophic relationships Figure 6 shows the percentage dry weight of food organisms in the stomach contents taken from samples of between IO and 50 specimens of each species. The planktonic feeders showed varying dependence on copepods, while the benthos feeders showed varying dependence on polychaetes. The numbers of molluscs found in the stomachs was small in comparison with their abundance in the benthos and the main predators of these were epibenthic invertebrates, particularly starfishes. Orthopristis, Odontoscion and Lagocephalus were epibenthos consumers, the last feeding on Callinectes which it crushed with powerful dental plates. Demersal fish which fed epibenthically were characteristic of San Luis where there was an abundant weed fauna but in Las Maritas the diet of the demersal fish was mainly benthic infauna. Sphyrama and Strongylura consumed only Jenkinsia while Caranx and Oligoplites had a less specialized diet which included mysids. Mugil was the dominant herbivore consuming benthic diatoms together with quantities of sand and Nichols&a consumed macroalgae, such as Enteromorpha, with attached epifauna.
R. R. C. Edwards
314
Piorengulo
Afhermomorus
Jsnkirvio
100
Sphyroeno
Pfoemuton bosctmwe
Sardinello
Dscoplcrus
Anchoo
Oiigopfiirs
Strongytura
50
0
Eucinortomus
MUllUS
Ho?muton ourolineotum
100
Umbrino
Hormulon steidnocheri
Orthooristis
Odontoscion
50
0
Logocephofus
Mugif
Nicholsino
100
50
0
Copcpodo
Mysidocea
Decovoda
w
Cladacero Oslrocodo
Amphipodo
Polycharla
Mircellonrous
Figure 6. Fish stomach contents as percentage
Algor
dry weight of ingested food.
Two Caribbean marine ecosystems. I
31.5
The diets described here are in general agreement with those of Randall (1967) for Caribbean reef fishes where related species have been studied. Discussion From these observations it is apparent that the fauna at each locality was distinct with regard both to biomass and dominant species. The intertidal fauna at San Luis was dominated by Donax and Emerita, the former being an active migrant, whereas the fauna at Las Maritas was dominated by Heterodonax, a non-migratory form. It is likely that both wave action and the sediment content of the water accounted for the faunistic differences between the two beaches. San Luis may be described ecologically as a high energy window where large quantities of water deposited on the beach by wave action filter through the sand leaving suspended material behind. In Las Maritas these conditions were not found. In the sublittoral the biomass of infauna was lower at San Luis and contained fewer species than in Las Maritas. The epifauna was distinct at the two localities, the absence of starfish at San Luis probably being related to the scarcity of bivalve molluscs and the anaerobic nature of the substrate. Here deposit-feeding echinoderms such as Mellita were found. The decapod Callinectes is normally found in lagoons and estuaries so that its presence in San Luis may be taken as an indication of conditions favouring high sedimentation rates. Fourteen of the fish species were common to both areas but the dominant types were distinct. The lower biomass at San Luis may be explained in terms of avoidance reactions to the contaminated water rather than by differences in food supply. For the herbivores there was an abundant food supply in San Luis in terms of macroalgae although the types found there may not have been the preferred diet of these fish. Conclusions (I) The fauna at two shallow water localities in eastern Venezuela was studied. One locality was subjected to domestic effluent from a city discharge whereas the other was situated in an inlet distant from the discharge point. (2) The average sublittoral biomass of benthic infauna at San Luis, the polluted beach, was 3247 g dry weight/ma, and the littoral biomass was 2.984 g/m2. For the unpolluted beach-Las Maritas-the figures were 5.839 and 1.079 g, respectively. Sublittoral epifauna averaged 0.916 g/me at both localities. (3) Fish biomass was 5,048 g/m2 at Las Maritas and 1.200 g/m2 at San Luis and the difference may have been related to avoidance reactions to effluent on the latter beach. (4) The littoral biomass was dominated by bivalve molluscs on both beaches and the sublittoral biomass by polychaetes. Bivalve molluscs were second in order of importance in the sublittoral biomass of Las Maritas, whereas gastropods were at San Luis. (5) The taxonomy and trophic relationships of the fauna were studied. At least 85 species of macrobenthos and 49 species of fish were present at the combined localities. The infauna in the sublittoral at San Luis contained about half the number of identifiable species that were found in Las Maritas. It is suggested that the anaerobic bottom conditions at the former locality may account for this difference. Acknowledgements The author wishes to thank A. Angel, P. Figueroa, F. Mendez, H. Mendez and B. Marcano of the Instituto Oceanografico for their considerable technical support while this work was
R. R. C. Edwards
316
in progress. Identifications of invertebrates were made by 0. Macsotay (UDO, Venezuela), C. H. Long and L. Coolidge (Harvard, U.S.A.) and A. Eleftheriou (Aberdeen, U.K.). Biochemical analyses were done by D. M. Finlayson (Aberdeen, U.K.). This study was done while the author was on secondment from the Department of Agriculture and Fisheries for Scotland, Marine Laboratory, Aberdeen, to the Overseas Development Administration, Foreign and Commonwealth Office, London. References Ansell, A. D., Sivadas, P., Narayanan, B., Sankaranarayanan, V. N. & Trevallion, A. 1972 The ecology of two sandy beaches in South West India. I. Seasonal changes in physical and chemical factors and in the macrofauna. Marine Biology 17, 3842. Brawn, V. M., Peer, D. L. & Bentley, R. J. 1968 Caloric content of the standing crop of benthic and epibenthic invertebrates of St Margaret’s Bay, Nova Scotia. Journal of the Fisheries Research Board of Canada 25(g), 1803-1811. Bunt, J. S., Lee, C. C. & Lee, E. 1972 Primary productivity and related data from tropical and subtropical marine sediments. Marine Biology 16, 28-36. Christensen, A. M. 1970 Feeding biology of the sea-star Astropecten irregularis Pennant. Ophelia 8, I-134.
Curl, H. 1960 Primary production measurements in the north coastal waters of South America. Deep Sea Research 7, 183-189. Edwards, R. R. C. 1973 Production ecology of two Caribbean marine ecosystems. II. Metabolism and energy flow. Estuarine and Coastal Marine Science I, 319-333. Edwards, R. R. C., Finlayson, D. M. & Steele, J. H. 1969 The ecology of O-group plaice and common dabs in Loch Ewe. II. Experimental studies of metabolism.Journal of Experimental Marine Biology and Ecology 3, 1-17. Fukuoka, J. 1965 Coastal upwelling near Venezuela. I. Year to year change of upwelling. Boletin de1 Institute Oceanografico, Cumana’, Venezuela. 4 (2), 223-233. Griffiths, R. G. & Simpson, J. G. 1972 Upwelling and other oceanographic features of the coastal waters of north eastern Venezuela. Serie Recursos y Explotacion Pesqueros 2, No. 4. Republica de Venezuela, Ministerio de Agricultura y Cria, Oficina National de Pesca. Hammer, L. 1967 Die PrimZirproduktion im Golf von Cariaco (ost-Venezuela). Internationale Revue der gesamten Hydrobiologie und Hydrographic 52 (5), 757-768. Hargrave, B. T. 1969 Epibenthic algal production and community respiration in the sediments of Marion Lake. Journal of the Fisheries Research Board of Canada 26 (8), 2003-2026. Hellier, T. R. 1958 The drop net quadrat, a new population sampling device. Publications of the Institute of Marine Science 5, 165-169. Hobson, E. S. 1973. Die1 feeding migrations in tropical reef fishes. Helgokikder wissenschaftliche Meeresuntersuchungen 24,361-370. McIntyre, A. D. & Eleftheriou, A. 1968 The bottom fauna of a flatfish nursery ground. Journal of the Marine Biological Association of the United Kingdom 48, I 13-142. Okuda, T., Benitez, J. A., Garcia, A. J. & Fernandez, E. 1968 Condiciones Hidrograficas y Quimicas en La Bahia de Mochirna y La Laguna Grande de1 Obispo desde 1964 a 1966. Boletin del Institute Oceanograjico, Cum&, Venezuela 7 (2) 7-37. Randall, J. E. 1967 Food habits of reef fishes of the West Indies. Studies in Tropical Oceanography, Miami No. 5, 665-847. Rodriguez, G. 1959 The marine communities of Margarita Island, Venezuela. Bulletin of Marine Science of the Gulf and Caribbean p (3), 237-280. Strickland, J. D. H. & Parsons, T. R. 1968 A manual of sea-water analysis. Bulletin of the Fisheries Research Board of Canada 167, 1-31 I. Trueman, E. R. 1971 The control of burrowing and the migratory behaviour of Donax denticulatus (Bivalvia: Tellinacea) Journal of the Zoological Society of London 165, 453-469. Wade, B. A. 1967 Studies on the biology of the West Indian beach clam, Donax denticulatus Linne I. Ecology Bulletin of Marine Science of the Gulf and Caribbean 17, 14~174.
Two Caribbean
marine
ecosystems. I
317
Appendix TABLE AI. Fauna1 list of invertebrates Las Maritas MOLLUSCA Bivalvia Abra lioica Dal1 Cod&u untillurum (d’orbigny) Crenellu divaricutu Orbigny Diplodontu punctutu Say Donux denticulatus LinnC Ervilliu nitens Montagu Ervilliu venezuelana Weisbord Heterodonux bimaculutus Linn6 Lawicardium luevigatum Linne Lucinu trisulcutu Conrad Lyonsia sp Musculus lateralis (Say) Pandora bushiunu Dal1 Pitur fulminutu Menke Solemya occident&s Deshayes Strigillu pisiformis Linne Tellina cristallinu Spengler Tellinu lineuta Turton Yoldia perprotructu Dal1 Gastropoda Alabina cereolu Weisbord Anuchis crussilabris (Reeve) Bittium sp Coma juspideus Gmelin Cymutium sp Hyalinu tenuilubra Tomlin Jespidea jespidella (Gmelin) Olivu reticularis Lamarck Olivella minuta Link Persiculu lavelleuna Orbigny Strombina sp Turbonilla sp Scaphopoda Cudulus quudridentutns Dal1 Dentulium sp Cephalopoda octopus sp POLYCHAETA Armundia sp Capitellidae Cerutonereis mirubilis Kinberg Chaetopteridae Chone sp Cirratulidae Diopatra sp Go&da sp Glyceru sp Lumbrineris sp Mugelonu sp Maldanidae Megalomma bioculatum (Ehlers) Nephtys sp
+ + + +
-
c i + +
-
-
-
+
i t -
+ -1. +
+ +
+ + + + + -t + -t + t -1 + + + i -c + + I + + +
Las Maritas
San Luis
+
+ I
from the two beaches
+ + -
Orbinia sp Onuphis holobrunchiuta Marenzeller Oweniu sp Pectinaria regulis Verrill Phyllodocidae Polynoidae Scolelepis sp Spionidae sp Syllidae Terebellidae Travisiu sp CRUSTACEA Amphipoda Ampeliscidae Calliopidae Haustoridae Lyssianassidae Copepoda Harpacticoidea
+ +
I + + ; +
-I+ + + i-
Decapoda Caluppa sp Cullinectes sp Emerita holthuisi Sankolli Ocypode sp Petrochirus sp Penueus sp Hoplocarida Squillu sp
-t + + -i -c
+ -
Isopoda Excirolunu
sp
i-
Mysidacea
spp
-i
-
+
+
+ +
+ +
: + +
Tanaidacea
+
spp
ECHINODERMATA Astropecten sp Holothuriu sp Luidia sp Mellita sexiesperforutu Ophiuroidea Oreaster sp
Leske
CEPHALOCHORDA Amphioxus sp Others : COELENTERATA Renilla sp
+ + -t + -t
spp.
+ -
+ + +
NEMERTINEA
+
SIPUNCULOIDEA
+
San Luis
R. R. C. Edwards
TABLE AZ. Fauna1 list of fishes from the two beaches Las Maritas Anchoa sp Anchoviella estauquae Archosargus rhomboidalis (L) Atherina sp Atherinomorus stipes (Miller and Troschel) Bairdiella ronchus (Cuv. and Valenc.) Caranx hippos (L) Chaenopsis sp Dactylopterus volitans (L) Dactyloscopus tridigitatus Gill Decapterus punctatus (Agassiz) Diapterus rhombeus (Cuv.) Diodon hystrix L Diplectrum formosum (L) Diplodus argentaeus (Valenc.) Elops saurus L Emblemaria pandionis Evermann and Marsh Eucinostomus argentaeus Baird and Girard Gobionellus sp Haemulon aurolineatum Cuv. and Valenc. Haemulon boschmae Metzelaar Haemulon steindachneri (Jordan and Gilbert) Harenguln clupeola (Cuv.) Hemipteronotus novacula (L) Hemirhamphus brasiliensis (L) Jenkinsia Zamprotaenia (Gosse) Lagocephalus laevigatus (L) Mugil curema Cuv. and Valenc. Mullus auratus Jordan and Gilbert Nicholsina usta (Cuv. and Valenc.) Odontoscion dentex (Cuv. and Valenc.) Oligoplites saurus saurus (Bloch and Schneider) Ophioscion sp Opistognathus sp Opisthonema oglinum (Le Sueur) Orthopristis ruber (Cuv. and Valenc.) Paralichthys tropicus Ginsburg Pamatomus saltatrix (Linnaeus) Rachycentron canadum (Linnaeus) Sardinella anchovia Cuv. and Valenc. Scomber colias Jordan and Evermann Selene vomer (L) Sphoeroides spengkri (Bloch) Sphyraena picudilla Poey Strongylura marina (Walbaum) Syngnathus rousseau Kaup Trachinotus falcatus (L) Umbrina coroides Cuv. and Valenc. Xenomelaniris brasiliensis Quoy and Gaimard p = plankton
+ + -+ + -+ + -+ --+ -+ + + ‘+ + + + + z+ -+ + + -+ -+ --+ -+ --+ + --+ -+
San Luis
Trophic group
+ f f f + -I-
P
+ ++ Jr-
+ + + : i+ + + + + : + + + ++ + : + -
feeder ; fc= fish carnivore ; b= benthos feeder ; h= herbivore.
b” P P f9: b b b P b b b b fc b b b b P b f: P P b h b h b fc b b iit b :: f9: fc b fc fc b fc b P
and Coastal
Marine
Science
(1973),
I, 303-318
Production Ecology of Two Caribbean Marine Ecosystems I. Physical
Environment
and Fauna
R. R. C. Edwards” Institute
Oceanografico,
Received
2
July
Universidad
de Oriente,
Cumand,
Venezuela
197.3
A quantitative study was made of the invertebrate macrofauna and fish fauna of two shallow water ecosystems. One was in an inlet on a clean sand bottom (I) while the other was on a muddy bottom (2) near a discharge point for domestic effluent. The largest average biomass of littoral infauna of 2.894 g/m* dry flesh weight was found at (2) while the largest average biomass of sublittoral infauna of 5.839 g/m* was found at (I). Fish biomass was 5.048 g/m= at (I) and 1-200 g/m* at (2) suggesting an avoidance reaction to the contaminated water at the latter locality. Diets of demersal fish were predominantly benthic infauna at (I) and epifauna at (2), the latter being related to the presence of a prolific weed fauna in the sublittoral.
Introduction This paper gives basic information collected as part of an ecological energetics study of coastal marine ecosystems in Venezuela. Fukuoka (1965) and Griffiths & Simpson (1972) showed that the region was subjected to seasonal upwelling and high values of primary production obtained by Curl (1959) and Hammer (1967) may be taken as further evidence of enrichment of the coastal waters. Relatively little is known of the marine fauna in this locality although Rodriguez (1969) made some taxonomic and intertidal studies on Margarita Island. Two beaches near Cumanl were chosen for the study (Figure I), one situated near the city and receiving domestic efBuent and the other situated 20 km to the west in a protected inlet.
Methods Intertidal and sublittoral infaunas were sampled with o-25 ms quadrats along continuous transects. Sublittoral samples were taken with SCUBA by transferring bottom deposits to a submerged container. The deposits were passed through a sieve of 1*4-mm mesh size at the surface and the sample preserved in 10% formaldehyde. Epibenthos was sampled by randomly placed 0.25 m2 quadrats on the sea bed, or by measuring squares 3 m x 3 m with a graduated cord. Animals on the surface of the deposit “Present address: Dept. Isle of Man, U.K.
of Marine
303
Biology,
University
of Liverpool,
Port Erin,
R. R. C. Edwards
304
were counted and identified and burrowing forms (e.g. holothurians) were uncovered by probing the bottom. Samples were removed for further study and preserved. Fish populations were sampled with a beach seine net of 25-m length and 3-m depth with a stretched mesh of 1.5 cm in the wings and 0.5 cm in the bag. Each haul was made from a distance of 70 m from the shore and covered an area of approximately 800 m2. Occasional samples of pelagic fish were obtained with rotenone poison. Dry flesh weights were obtained by removing stomach contents and hard parts, such as shells. In the case of echinoderms containing calcareous skeletal material, flesh weights were obtained by rapid combustion at 500 “C for 30 min. Prolonged combustion was avoided since it may lead to errors as a result of decomposition of the skeletal material. Caloric
40’
64OOO’
30’
30’
CAR/SBEAN
SEA
GULF
OF
CAR/AC
Venezuela 100 00’
Figure
r. Location
of sampling area on coast adjacent to Cumani.
Two Caribbean marine ecosystems. I
305
contents were calculated from analyses of protein, lipid and carbohydrate using methods described by Edwards et al. (1969). Physical
environment
San Luis This beach was 5 km in length and lay in a north east/south west direction in front of a suburb of the city. About half way along there was an opening into a small lagoon system. The beach received moderate wave action created by the north east trade winds. This produced a current running in a south west direction along the beach, which dispersed domestic effluent from a discharge point at the north east end. The profile given in Figure z shows that the depth increase was relatively gradual and the littoral zone was about 7 m in horizontal extent. Analyses of particle sizes of the beach and the bottom at 1-m depth are shown in Figure 3. Below 2 m the bottom sediment was anaerobic mud. Sorting coefficients were calculated from the expression z2/Q3/Q1 where Qi and Qa were the first and third quartiles of the cumulative curve. For the beach and sublittoral these were 1.46 and 1.91 suggesting that the former was better sorted than the latter.
70-
\
.
9IO-
\ I 0
I
II 10
I 20
I
I 30
I
Distance
I 40
I
I 50
II
11 60
. 1
70
1 80
Cm)
Figure 2. Depth profiles of Las Ma&as and San Luis beaches. (C.D. =chart -O-O-, San Luis; -@-@-, Las Maritas.
datum).
Las Maritas This beach was situated just inside the inlet Bahia de Mochima which faced north into the Caribbean about 20 km to the west of Cumanb. Its hydrography and physical characteristics were described by Okuda et al. (1968). Th e b each lay on the east side of the inlet and was protected from the prevailing winds with the result that wave action was slight. It was about 200 m in length and 12 m in extent with a rocky shore on either side which extended for a short distance into the sublittoral. The sublittoral profile of Las Maritas (Figure 2) is steeper than San Luis. Particle size analysis of the beach and sublittoral sand are shown in Figure 3. Sorting coefficients for the beach, 4 m and II m depth, were 1.22, 1.73 and 1.50, respectively.
306
R. R. C. Edzcards
Temperature, salinity and dissolved oxygen in the water in Mochima were measured by Okuda et al. (1968). The annual temperature range at depths less than 5 m was 22 to 29 “C, with the lowest temperatures in the upwelling period between December and April. For most of the year the surface water temperature was between 25 and 27 “C. Dissolved oxygen levels in the water varied with the time of day but were usually between 5.5 and 7.0 mg/l. Salinities were in the range 36.5 to 37.0%~ with very slight annual variation. Secchi disc readings at Las Maritas were normally between 15 and 20 m but during the period of upwelling and plankton blooms they were often reduced to 6 to IO m. At San Luis where there were quantities of suspended material in the water readings were 2 to 3 m.
80 !
5 60 ” &I a 40 i cn g 20
Particle
sze
(pm)
Figure 3. Cumulative curves of sand particle size. (a) Las Maritas: -tt, Beach mid-tide level; -O-O-, sublittoral 4-m depth; -V-V-, sublittoral 11-m depth. (b) San Luis: -@-a-, beach mid-tide level; -O-O-, sublittoral 1-m depth. Detritus contents
In Las Maritas at 4-m depth the combustible detritus content of the sand to a depth of IO cm was 158 g dry wt/m2 and at II m depth 117 g. In San Luis at 2 m depth the content was very high at 2192 g/m2, suggesting that deposition on this beach was exceeding breakdown of the sedimentary material by biological action. Chlorophyll
a measurements
These were made following Strickland & Parsons (1968). The quantity of chlorophyll a in the surface I m of sand at 4 m in Las Maritas was 35.4 mg/m2 in the bare sand areas and 114.4 mg in the Enteromorpha zone. At 11-m depth where there were no macroalgae the chlorophyll a content was 25.5 mg/m2. In San Luis beach 21.0 mg/m2 was measured, but this did not include the macroalgae. Bunt et al. (1972) gave estimates of 20-200 mg/m2 with a mean of 69 mg/m2 for shallow water Caribbean deposits. The mean value for Las Maritas of 75 mg/m2 compares closely with this figure. The macrobenthos
The results of the littoral and sublittoral surveys of both beaches are given as biomass and numbers in Tables I, 2 and 3, and depth distribution in Las Maritas is shown in Figure 4. A fauna1 list is given in Appendix Table AI.
Two Caribbean marine ecosystems. I
307
The littoral fauna Las Maritas. The littoral fauna on this beach was dominated by the bivalve mollusc Heterodonax which inhabited a zone at and above mid-tide level. The biomass of the fauna was highest at mid-tide level where the density of this bivalve was greatest. The isopod Excirolana
was the dominant crustacean and occurred throughout the littoral zone. Scolelepis was the dominant polychaete and Amphioxus was present on the lowest part of the beach. The ghost crab Ocypode was found just above the high water mark with a density of about 3 and a dry flesh weight of 1.8 g per metre of shore line. A mean biomass figure for the beach fauna was I ‘079 g dry wt/ms. San Luis. The dominant member of the fauna was Donax denticulatus, which was a typical inhabitant of exposed beaches in this region. The smaller individuals lived highest on the beach (Wade, 1967), the maximum density being at 0.75 m above low water. The dominant crustacean between low water and mid-tide was Emerita holthuisi while the isopod Excirolana occurred above mid-tide level. The dominant polychaete was Scolelepis. Ocypode had a density of 0.2 and a dry flesh weight of 0.13 g per metre of shore line. A mean biomass figure for the beach fauna was 2.894 g dry wt/m2.
23456-
12 13 14 15 16 -
I I
Scale
5&e-%0
Figure 4. Depth distribution of predominant macrofauna in Las Maritas. Scale indicates numbers of individuals per m2 before correction for sampling errors. (C.D.=chart datum.)
Comparison of the beaches
The absence of Donax in Las Maritas may relate to the very slight wave action, which did not permit the normal wave-dependent migratory behaviour (Trueman, 1971). Heterodonax did not show this behaviour and was adapted to sheltered beaches. The filter-feeding
R. R. C. Edwards
Emerita was more common in San Luis where the water contained suspended material. The total biomass (excluding Ocypode) per metre transect in Las Maritas was 12.95 g and in San Luis zo*16 g but if Ocypode was included became 14.70 g and 20.29 g, respectively, Ansell, et al. (1972) found maximum biomasses on Indian beaches 2 to 3 times those in San Luis. Sublittoral infauna Owing to the method of sampling in which deposit was removed with a scoop, some members of the infauna, particularly crustaceans, escaped. To correct for this, a series of 48 cores were taken at 5-m depth in Las Maritas and the macrofauna was pooled and weighed. It was calculated that 0.41 of the benthic biomass was lost with the scoop method due to sampling and sieving errors. Las Maritas. The biomass of the fauna increased from I m to 5 m depth (Table 2) and thereafter declined. At depths below 12 m, which was about the depth of the thermocline, the biomass of infauna was low and some species showed a marked decline in numbers or a discontinuity of distribution (Figure 4). TABLE I. Biomass as g dry flesh wt and numbers beaches Las Maritas
0.75 m
1-0 m
Bivalvia Gastropoda Crustacea Polychaeta Cephalochorda Total
No.
Dry wt
No.
-
-
-
16
0.016
-
16
0.016
12 64 36
II2
Dry wt
per m2 of littoral
Metres above C.D. 0.50 m No.
Dry wt
0.296
332
6.653
-
-
-
64
0.028 0’012
0,040 0.090
fauna on both
0.25 m
No. 92 48
Drywt
0.0 m No.
-
-
-
0.007
464
0’252
-
-
-!
-
-
-
0.336
397
6.783
140
0.259
Dry wt
4
0.003 0’095 -
4 472
0’003 0’101
San Luis 1.0 m No. Bivalvia Crustacea Polychaeta Total
Dry wt
No.
Dry wt
No.
-
-
296
0.264
1564 84 72 1720
2.640 0’297 0.067 3.004
1116 I92 52 1360
-
-
296
0.264
0.25 m
0.50 m
0.75 m
Drywt 3.814 3.336 0.073 7’223
No.
Dry wt
14.4
3.716 0.004 0.146 3.866
4 116 264
0.0 m No. 92 92
Dry wt 0.115 0.115
The sublittoral biomass was dominated by polychaetes followed by molluscs, gastropods, cephalochordates (Amphioxzcs), sipunculids, crustaceans and scaphopods, in that order. A corrected mean figure for sublittoral biomass to a depth of 16 m was 5.839 g/m2. San Luis. The slope of this beach (Figure 2) was less than Las Maritas and thus fewer sublittoral stations were sampled. When correction was made for loss of sublittoral infauna due to sampling errors, the biomass of the beach and the sublittoral was about the same. A corrected mean figure for the sublittoral biomass was 3.247 g/m2. The dominant member of the infauna by weight was the polychaete Diopatra followed by the gastropod Olivella minuta. The infauna was less diverse than in Las Maritas (Appendix Table AI) which may result from the anaerobic bottom conditions.
Two Caribbean marine ecosystems. I
309
One of the few quantitative studies of the fauna in the immediate sublittoral of sandy beaches is that of McIntyre & Eleftheriou (1968) in Scotland. Their mean littoral biomass estimates corresponded with those in Las Maritas while their sublittoral estimates were approximately half those of the latter beach. Sublittoral
epibenthos
In Table 4 are given the mean numbers and dry flesh weights of the epifauna to a depth of IO m. The animals in this Table were those of common occurrence and some species, e.g. holothurians, the decapod Calappa and the hoplocaridan Squilla, are not included. The epifauna were generally of larger body size than the infauna and their distribution was not closely related to depth. Members of the epifauna were sparse between low water and I m although it was in this zone that Squilla was found. This had a density of 0.26 per metre of shore line and a flesh dry weight of 0.97 g.
Las Maritas.
TABLE
2. Biomass as g dry flesh wt and numbers
per ma of sublittoral
infauna in Las Maritas
Metres below C.D. Dry :tm Polychaeta Bivalvia Gastropoda Scaphopoda Crustacea Ophiuroidea Sipunculoidea Cephalochorda Others Total
0’21 I
0.063 0.572 -
0’202
I ‘072
8m Dry wt Polychaeta Bivalvia Gastropoda Scaphopoda Crustacea Ophiuroidea Sipunculoidea Cephalochorda Others Total
No.
3.343 0’779 0.024 0.024
0.650 0.513 0.017
-
684 172 40
0,007
16
0’051 0.123 0,019
72
88 -
0’012
4.693
12 16
16 468
0.432 -
No.
Dry wt
1.812
Dry :tm
No.
Dry wt
No.
3’270 0.876
1404
3’388
1580
0.007 0.035
856 2.195 228 68 32 7i 120
8 2
I394
256 1.894
0’120
72 if 48 204
0.261
0.621 0'012
0.030 0.180
2078
0’752 0.473 0.076 7.426
Dry wt
No.
Dry wt I .626 0.126 0'010
36 I:048
0.434 0.322 0.080 5’405
No. 1492
10 m
0.016
0.064 0.349 0.082
5m
No.
284 44 36
0.024 -
2m Dry wt
16 2
12 m
0.410 0.061 0.116
-
0.895
428 112
128
108 100
-
0.039 0.098 0.391 -
-
44
0’001 0.071
3’310
2192
2'012
4 112
2.609
48
4 4 16
0’003 0.060 0.034 0.070
-
-
820
I’929
Dry w:”
1520
564 64
1.641 0.716
364
16
0.036
48 I44
96 68 204 48
108
0’101
2650
0.280 0.342 o-194 0.260 6.179
No.
Dry wt
IO
16
176 28
2.813 0.614
720 I32
1'593 0.016
20
48 36 4 104 36
24
52 93
0.085 -
-
2405
5.381
1108
No.
Dry wt
No.
0.861 0*0x8 0’010 0’002
3.52 40
0.671 0.128
276 44
12
0,043
12
0’002
0.072
100 16
8 96 36
-
0’010 0’002 0’022 -
688
1.087
12
56
0.055 0’102 0.103
4
4 4 532
0.024 o-39 0.018
0’92.5
The starfishes Astropecten and Luidia remained buried in the sand during the day and emerged at dusk. The gastropods Oliva and COWSshowed burrowing behaviour, whereas Strombina was normally found only on the surface of the sand. Eleftheriou (personal communication) found that starfish and hermit crabs were the dominant
epifauna
in the sublittoral
of a sandy
beach
in Scotland.
estimates were about 0.17 of those observed in Las Maritas.
His
12
16 m
15 m
448
No.
I
14m
256 0.327 156 0.595
0.084 0.038 0’001
6m Dry wt No.
starfish
biomass
-
8
480
310
R. R. C. Edwards
San Luis. Most of the epifauna on this beach was associated with the macroalgae Enteromorpha, Ulva and Ectocarpus, and was composed of small crustacea and molluscs. The blue crab Callinectes was sampled from seine net hauls but its burrowing behaviour may have resulted in underestimates. The epifauna of occasional occurrence, for example Mellita, Callapa, Oreaster and Octopus, were not included in biomass estimates.
The abundant meio- and microfauna of the weed, including harpacticoid copepods, nematodes, turbellarians, ciliates and protozoans were not estimated since in total biomass the meio- and microfauna is small (Hargrave, 1969). TABLE 3. Biomass as g dry flesh wt and numbers per m2 of sublittoral San Luis
infauna in
Metres below C.D. Dry km
No.
1.187
356 62 104
Polychaeta Bivalvia Gastropoda Scaphopoda Crustacea Nemertini Coelenterata Sipunculoidea Ophiuroidea
0’020
Total
1.854
0’133
0’313 0.051 0.084 0.066 -
Dry :tmNo. I 228 0.075 0.650
268 26
334 4 48
0’021
I2 120 I
-
Dry :tmNo.
0,025 0.230 0.162
2
0’012
2
0.016
6572
2.419
69;
0.749 0.015 0.446 0.007 0’01 I 0.167 0.028 0.028 -
404 4 180
I.451
692
62” I 2
37 -
TABLE 4. The biomass and numbers per m2 of the predominant
Conus
Coelenterata
Pettochirus Oliwa Strombina Total
epifauna
San Luis
Las Maritas
Astropecten Luidia
benthic
Dry flesh wt (g)
No.
0’440 0’330 0.042 0’033 0.03 I 0.030 0.008 0.914
0.08 0.03 0.82 0.09 3’70 0.09 0.25 5.06
Dry flesh wt (g)
Alabina
No. 3600
MuSCUlUS
0.780 0.058 0.036 0’030 0.007 0.006
Total
0.917
5059’01
Amphipoda Mysidacea
Calliflectes Diopatra
1000
243 0’010
27 189
Comparing the two beaches it can be seen that the biomass of epifauna was the same but the epifauna in San Luis consisted of a large number of small animals associated with the weed whereas that in Las Maritas consisted of a small number of larger animals. This difference may be related to the food supply of the epibenthos being mainly plant material in San Luis and benthic infauna in Las Maritas. Caloric contents of the macrobenthos were calculated from values given by Brawn et al. (1968) and used in Edwards (1973). Trophic relationships of the macrobenthos
Examinations of stomach contents were made on a qualitative basis only, 23 species representative of all phyla having been examined. The majority of the sublittoral infauna from
Two Caribbean marine ecosystems. I
311
both beaches appeared to be detrital feeders and the stomach contents were almost indistinguishable from detritus samples taken from the corresponding sediments. The most commonly identifiable contents were diatoms, foraminifera, fragments of crustaceans and a amorphous organic material which may have been faecal in origin. In the epifauna Astropecten, Luidia and Calh’nectes were observed to be predators on epiand infauna. Callinectes consumed the gastropod Olivella, polychaetes and bivalves. Astropecten consumed bivalve molluscs (mostly Pitar) gastropods and polychaetes while Luidia consumed polychaetes and small ophiuroids. Christensen (1970) concluded that Astropecten irregularis was a selective predator on bivalves, preferring juveniles or species with low resistance to anoxia, which were more rapidly digested. Since Pitar was uncommon in the benthos its preferential selection by Astropecten could be explained in this way. In the littoral fauna Donax, Heterodonax, Emerita and Scolelepis consumed planktonic diatoms and detrital material while Excirolana consumed crustacean larvae. Fish populations
The majority of the fishes caught on both beaches were migratory types and were probably in continual motion between different beaches along the coast. They were categorized according to their feeding habits: (I) plankton feeders, e.g. Jenhinsia; (2) fish carnivores (i.e. consumers of other fish), e.g. Strongylura; (3) benthos feeders, e.g. Eucinostomus; (4) herbivores, e.g. Mugil. Because the juveniles of many of the demersal fishes feed planktonically, separation into these categories is somewhat artificial but provides a basis for food chain analysis. There were at least 31 species in Las Maritas and 32 in San Luis (Appendix Table Aa). Biomass and numbers
The results of the beach seine net surveys on both beaches are given in Table 5 and are expressed as biomass in Figure 3. In San Luis the net sampled the entire water column but only the lower 3 m in Las Maritas which may have resulted in under-estimates of the planktonic fishes. In view of this, biomass estimates of these fish were calculated from catches TABLE 5. Mean numbers June 1972
of fish per net haul during
Dec./Feb.
Mar./May
the period
June/Aug.
Nov.
Sept./Nov.
Las Maritas No. hauls Plankton feeders Fish carnivores Benthos feeders Herbivores Total
7 277 5 24 5 361
4 9r 2
44 2
139
5 1984 36 rr4 4 2138
5 r4g r7 29 17 211
San Luis No. hauls Plankton feeders Fish carnivores Benthos feeders Herbivores Total
II
78
4 8
I
IO
20
25 I
100
I 44
7 32 30 45 7 II4
3
165 8: 20 279
1970 to
312
R. R. C. Edwards
made on two occasions in Las Maritas when the shoals were observed close to the shore. Opistognathus and Chaenopsiswhich inhabited burrows were not sampled by the net. These together with Gobionellus, which was not captured by the net, were estimated by underwater counts. In order to correct for the efficiency of the net a number of the abundant Haemulon aurolineatum were marked with pelvic fin clips, released into the water as the net approached the shore, and the number recovered in the subsequent haul was counted. During two tests a total of 70 fish were released and 37 were recovered. The method was only approximate since the fish were stressed by previous capture and handling but it gave a measure of the extent of the escapage at the water’s edge where losses occurred below the ground rope. When planktonic fish were excluded from Table 6 the numbers taken in Las Maritas were highest in June/August and lowest in December/February while in San Luis they were highest in September/November and lowest in March/May.
Figure 5. Biomass of fish fauna before correction for gear efficiency. n , Plankton consumers; E, benthos consumers; 1111, fish carnivores; \\\ , herbivores.
Figure 5 shows that total fish biomass in Las Maritas was four times that in San Luis. Part of this difference may relate to differences in food supply for each trophic grouping which, except for the herbivores, was lower in San Luis but part may also be attributed to an avoidance reaction to the contaminated water on the latter beach. In correcting for gear efficiency the dry weights in Figure 5 should be doubled to obtain an approximate estimate of true biomass. The figures for Las Maritas agree closely with those of Hellier (1958) for shallow bays in Texas. Hobson (1973) observed that the numbers of fishes on sandy bottoms at night increased as a result of emergence of fish from adjacent coral areas but the effect of this was probably small in Las Maritas since nearby coral colonies were poorly developed. About 0.6 of the demersal fish biomass in Las Maritas was attributed to fish of small body size, particularly Chaenopsis and Gobionellus, a factor important in energetics studies since these fish have proportionally high metabolic rates. Length/weight relationships and caloriJic contents Length and dry weight relationships are given in Table 6, being analysed in the form W= aX* after logarithmic transformation. Strongylura gave exceptional values which were attributed to the excessive jaw length (25% of standard length) resulting in high values of standard length.
Two Caribbean
marine ecosystems. I
313
Caloric contents were calculated from analysis of protein, lipid and carbohydrate and results of analyses of seven species are given in Table 7. The calorific contents lay in the range 4.59 to 5.14 kcal/g dry wt with a mean of 4.83 when calculated from accepted conversions. TABLE 6. Length/dry
H. aurolineatum H. steindachneri H. boschmae Orthopristis Eucinostomus Umbrina Mugil Nicholsina Oligoplites Strongylura Sphyraena Anchoa (immature) Anchoa (mature) Anchoviella Harengula Jenkinsia
TABLE
7. Biochemical
weight
of fish expressed in the form W= aX* No. specimens
a
b
0~0023 0.0038
64 46 74
0.0041
3.4396 3’2577 3’3215 3.1811
0’0025 0’004.4
3.4236 3.0986
132 62
0.0042 0.0038
3.1181
100
0.0028
58
84 66
3’1771 3.0183 I .8608 3.1316 3’3000 2.9830
45 58 69 49
0.0046
3.1558 3.1627
:i
O’ooIg
3.3632
91
0.0028 0.0217 0'0012
0’0013 0.0039
0’0020
analyses and caloric content
Protein H. aurolineatum H. boschmae Eucinostomus Mugil Oligoplites Strongylura Sardinella
relationships
67.51 66.17 73’24 71.80 68.78 80.13 70’14
of homogenized
mg/~oo mg dry wt Carbohydrate Lipid 0’59 0.48 0.53 0.74 0’53 0.71 0.48
Ash
9.36 8.83 10'00
22.73 23.65 15’95
7’42 6.90 5’40 7.46
23’71 13’94 21.63
20’00
fish
kcal/g dry wt 4.762 4.631 5’147 4.829 4.598
5’110 4’727
Trophic relationships Figure 6 shows the percentage dry weight of food organisms in the stomach contents taken from samples of between IO and 50 specimens of each species. The planktonic feeders showed varying dependence on copepods, while the benthos feeders showed varying dependence on polychaetes. The numbers of molluscs found in the stomachs was small in comparison with their abundance in the benthos and the main predators of these were epibenthic invertebrates, particularly starfishes. Orthopristis, Odontoscion and Lagocephalus were epibenthos consumers, the last feeding on Callinectes which it crushed with powerful dental plates. Demersal fish which fed epibenthically were characteristic of San Luis where there was an abundant weed fauna but in Las Maritas the diet of the demersal fish was mainly benthic infauna. Sphyrama and Strongylura consumed only Jenkinsia while Caranx and Oligoplites had a less specialized diet which included mysids. Mugil was the dominant herbivore consuming benthic diatoms together with quantities of sand and Nichols&a consumed macroalgae, such as Enteromorpha, with attached epifauna.
R. R. C. Edwards
314
Piorengulo
Afhermomorus
Jsnkirvio
100
Sphyroeno
Pfoemuton bosctmwe
Sardinello
Dscoplcrus
Anchoo
Oiigopfiirs
Strongytura
50
0
Eucinortomus
MUllUS
Ho?muton ourolineotum
100
Umbrino
Hormulon steidnocheri
Orthooristis
Odontoscion
50
0
Logocephofus
Mugif
Nicholsino
100
50
0
Copcpodo
Mysidocea
Decovoda
w
Cladacero Oslrocodo
Amphipodo
Polycharla
Mircellonrous
Figure 6. Fish stomach contents as percentage
Algor
dry weight of ingested food.
Two Caribbean marine ecosystems. I
31.5
The diets described here are in general agreement with those of Randall (1967) for Caribbean reef fishes where related species have been studied. Discussion From these observations it is apparent that the fauna at each locality was distinct with regard both to biomass and dominant species. The intertidal fauna at San Luis was dominated by Donax and Emerita, the former being an active migrant, whereas the fauna at Las Maritas was dominated by Heterodonax, a non-migratory form. It is likely that both wave action and the sediment content of the water accounted for the faunistic differences between the two beaches. San Luis may be described ecologically as a high energy window where large quantities of water deposited on the beach by wave action filter through the sand leaving suspended material behind. In Las Maritas these conditions were not found. In the sublittoral the biomass of infauna was lower at San Luis and contained fewer species than in Las Maritas. The epifauna was distinct at the two localities, the absence of starfish at San Luis probably being related to the scarcity of bivalve molluscs and the anaerobic nature of the substrate. Here deposit-feeding echinoderms such as Mellita were found. The decapod Callinectes is normally found in lagoons and estuaries so that its presence in San Luis may be taken as an indication of conditions favouring high sedimentation rates. Fourteen of the fish species were common to both areas but the dominant types were distinct. The lower biomass at San Luis may be explained in terms of avoidance reactions to the contaminated water rather than by differences in food supply. For the herbivores there was an abundant food supply in San Luis in terms of macroalgae although the types found there may not have been the preferred diet of these fish. Conclusions (I) The fauna at two shallow water localities in eastern Venezuela was studied. One locality was subjected to domestic effluent from a city discharge whereas the other was situated in an inlet distant from the discharge point. (2) The average sublittoral biomass of benthic infauna at San Luis, the polluted beach, was 3247 g dry weight/ma, and the littoral biomass was 2.984 g/m2. For the unpolluted beach-Las Maritas-the figures were 5.839 and 1.079 g, respectively. Sublittoral epifauna averaged 0.916 g/me at both localities. (3) Fish biomass was 5,048 g/m2 at Las Maritas and 1.200 g/m2 at San Luis and the difference may have been related to avoidance reactions to effluent on the latter beach. (4) The littoral biomass was dominated by bivalve molluscs on both beaches and the sublittoral biomass by polychaetes. Bivalve molluscs were second in order of importance in the sublittoral biomass of Las Maritas, whereas gastropods were at San Luis. (5) The taxonomy and trophic relationships of the fauna were studied. At least 85 species of macrobenthos and 49 species of fish were present at the combined localities. The infauna in the sublittoral at San Luis contained about half the number of identifiable species that were found in Las Maritas. It is suggested that the anaerobic bottom conditions at the former locality may account for this difference. Acknowledgements The author wishes to thank A. Angel, P. Figueroa, F. Mendez, H. Mendez and B. Marcano of the Instituto Oceanografico for their considerable technical support while this work was
R. R. C. Edwards
316
in progress. Identifications of invertebrates were made by 0. Macsotay (UDO, Venezuela), C. H. Long and L. Coolidge (Harvard, U.S.A.) and A. Eleftheriou (Aberdeen, U.K.). Biochemical analyses were done by D. M. Finlayson (Aberdeen, U.K.). This study was done while the author was on secondment from the Department of Agriculture and Fisheries for Scotland, Marine Laboratory, Aberdeen, to the Overseas Development Administration, Foreign and Commonwealth Office, London. References Ansell, A. D., Sivadas, P., Narayanan, B., Sankaranarayanan, V. N. & Trevallion, A. 1972 The ecology of two sandy beaches in South West India. I. Seasonal changes in physical and chemical factors and in the macrofauna. Marine Biology 17, 3842. Brawn, V. M., Peer, D. L. & Bentley, R. J. 1968 Caloric content of the standing crop of benthic and epibenthic invertebrates of St Margaret’s Bay, Nova Scotia. Journal of the Fisheries Research Board of Canada 25(g), 1803-1811. Bunt, J. S., Lee, C. C. & Lee, E. 1972 Primary productivity and related data from tropical and subtropical marine sediments. Marine Biology 16, 28-36. Christensen, A. M. 1970 Feeding biology of the sea-star Astropecten irregularis Pennant. Ophelia 8, I-134.
Curl, H. 1960 Primary production measurements in the north coastal waters of South America. Deep Sea Research 7, 183-189. Edwards, R. R. C. 1973 Production ecology of two Caribbean marine ecosystems. II. Metabolism and energy flow. Estuarine and Coastal Marine Science I, 319-333. Edwards, R. R. C., Finlayson, D. M. & Steele, J. H. 1969 The ecology of O-group plaice and common dabs in Loch Ewe. II. Experimental studies of metabolism.Journal of Experimental Marine Biology and Ecology 3, 1-17. Fukuoka, J. 1965 Coastal upwelling near Venezuela. I. Year to year change of upwelling. Boletin de1 Institute Oceanografico, Cumana’, Venezuela. 4 (2), 223-233. Griffiths, R. G. & Simpson, J. G. 1972 Upwelling and other oceanographic features of the coastal waters of north eastern Venezuela. Serie Recursos y Explotacion Pesqueros 2, No. 4. Republica de Venezuela, Ministerio de Agricultura y Cria, Oficina National de Pesca. Hammer, L. 1967 Die PrimZirproduktion im Golf von Cariaco (ost-Venezuela). Internationale Revue der gesamten Hydrobiologie und Hydrographic 52 (5), 757-768. Hargrave, B. T. 1969 Epibenthic algal production and community respiration in the sediments of Marion Lake. Journal of the Fisheries Research Board of Canada 26 (8), 2003-2026. Hellier, T. R. 1958 The drop net quadrat, a new population sampling device. Publications of the Institute of Marine Science 5, 165-169. Hobson, E. S. 1973. Die1 feeding migrations in tropical reef fishes. Helgokikder wissenschaftliche Meeresuntersuchungen 24,361-370. McIntyre, A. D. & Eleftheriou, A. 1968 The bottom fauna of a flatfish nursery ground. Journal of the Marine Biological Association of the United Kingdom 48, I 13-142. Okuda, T., Benitez, J. A., Garcia, A. J. & Fernandez, E. 1968 Condiciones Hidrograficas y Quimicas en La Bahia de Mochirna y La Laguna Grande de1 Obispo desde 1964 a 1966. Boletin del Institute Oceanograjico, Cum&, Venezuela 7 (2) 7-37. Randall, J. E. 1967 Food habits of reef fishes of the West Indies. Studies in Tropical Oceanography, Miami No. 5, 665-847. Rodriguez, G. 1959 The marine communities of Margarita Island, Venezuela. Bulletin of Marine Science of the Gulf and Caribbean p (3), 237-280. Strickland, J. D. H. & Parsons, T. R. 1968 A manual of sea-water analysis. Bulletin of the Fisheries Research Board of Canada 167, 1-31 I. Trueman, E. R. 1971 The control of burrowing and the migratory behaviour of Donax denticulatus (Bivalvia: Tellinacea) Journal of the Zoological Society of London 165, 453-469. Wade, B. A. 1967 Studies on the biology of the West Indian beach clam, Donax denticulatus Linne I. Ecology Bulletin of Marine Science of the Gulf and Caribbean 17, 14~174.
Two Caribbean
marine
ecosystems. I
317
Appendix TABLE AI. Fauna1 list of invertebrates Las Maritas MOLLUSCA Bivalvia Abra lioica Dal1 Cod&u untillurum (d’orbigny) Crenellu divaricutu Orbigny Diplodontu punctutu Say Donux denticulatus LinnC Ervilliu nitens Montagu Ervilliu venezuelana Weisbord Heterodonux bimaculutus Linn6 Lawicardium luevigatum Linne Lucinu trisulcutu Conrad Lyonsia sp Musculus lateralis (Say) Pandora bushiunu Dal1 Pitur fulminutu Menke Solemya occident&s Deshayes Strigillu pisiformis Linne Tellina cristallinu Spengler Tellinu lineuta Turton Yoldia perprotructu Dal1 Gastropoda Alabina cereolu Weisbord Anuchis crussilabris (Reeve) Bittium sp Coma juspideus Gmelin Cymutium sp Hyalinu tenuilubra Tomlin Jespidea jespidella (Gmelin) Olivu reticularis Lamarck Olivella minuta Link Persiculu lavelleuna Orbigny Strombina sp Turbonilla sp Scaphopoda Cudulus quudridentutns Dal1 Dentulium sp Cephalopoda octopus sp POLYCHAETA Armundia sp Capitellidae Cerutonereis mirubilis Kinberg Chaetopteridae Chone sp Cirratulidae Diopatra sp Go&da sp Glyceru sp Lumbrineris sp Mugelonu sp Maldanidae Megalomma bioculatum (Ehlers) Nephtys sp
+ + + +
-
c i + +
-
-
-
+
i t -
+ -1. +
+ +
+ + + + + -t + -t + t -1 + + + i -c + + I + + +
Las Maritas
San Luis
+
+ I
from the two beaches
+ + -
Orbinia sp Onuphis holobrunchiuta Marenzeller Oweniu sp Pectinaria regulis Verrill Phyllodocidae Polynoidae Scolelepis sp Spionidae sp Syllidae Terebellidae Travisiu sp CRUSTACEA Amphipoda Ampeliscidae Calliopidae Haustoridae Lyssianassidae Copepoda Harpacticoidea
+ +
I + + ; +
-I+ + + i-
Decapoda Caluppa sp Cullinectes sp Emerita holthuisi Sankolli Ocypode sp Petrochirus sp Penueus sp Hoplocarida Squillu sp
-t + + -i -c
+ -
Isopoda Excirolunu
sp
i-
Mysidacea
spp
-i
-
+
+
+ +
+ +
: + +
Tanaidacea
+
spp
ECHINODERMATA Astropecten sp Holothuriu sp Luidia sp Mellita sexiesperforutu Ophiuroidea Oreaster sp
Leske
CEPHALOCHORDA Amphioxus sp Others : COELENTERATA Renilla sp
+ + -t + -t
spp.
+ -
+ + +
NEMERTINEA
+
SIPUNCULOIDEA
+
San Luis
R. R. C. Edwards
TABLE AZ. Fauna1 list of fishes from the two beaches Las Maritas Anchoa sp Anchoviella estauquae Archosargus rhomboidalis (L) Atherina sp Atherinomorus stipes (Miller and Troschel) Bairdiella ronchus (Cuv. and Valenc.) Caranx hippos (L) Chaenopsis sp Dactylopterus volitans (L) Dactyloscopus tridigitatus Gill Decapterus punctatus (Agassiz) Diapterus rhombeus (Cuv.) Diodon hystrix L Diplectrum formosum (L) Diplodus argentaeus (Valenc.) Elops saurus L Emblemaria pandionis Evermann and Marsh Eucinostomus argentaeus Baird and Girard Gobionellus sp Haemulon aurolineatum Cuv. and Valenc. Haemulon boschmae Metzelaar Haemulon steindachneri (Jordan and Gilbert) Harenguln clupeola (Cuv.) Hemipteronotus novacula (L) Hemirhamphus brasiliensis (L) Jenkinsia Zamprotaenia (Gosse) Lagocephalus laevigatus (L) Mugil curema Cuv. and Valenc. Mullus auratus Jordan and Gilbert Nicholsina usta (Cuv. and Valenc.) Odontoscion dentex (Cuv. and Valenc.) Oligoplites saurus saurus (Bloch and Schneider) Ophioscion sp Opistognathus sp Opisthonema oglinum (Le Sueur) Orthopristis ruber (Cuv. and Valenc.) Paralichthys tropicus Ginsburg Pamatomus saltatrix (Linnaeus) Rachycentron canadum (Linnaeus) Sardinella anchovia Cuv. and Valenc. Scomber colias Jordan and Evermann Selene vomer (L) Sphoeroides spengkri (Bloch) Sphyraena picudilla Poey Strongylura marina (Walbaum) Syngnathus rousseau Kaup Trachinotus falcatus (L) Umbrina coroides Cuv. and Valenc. Xenomelaniris brasiliensis Quoy and Gaimard p = plankton
+ + -+ + -+ + -+ --+ -+ + + ‘+ + + + + z+ -+ + + -+ -+ --+ -+ --+ + --+ -+
San Luis
Trophic group
+ f f f + -I-
P
+ ++ Jr-
+ + + : i+ + + + + : + + + ++ + : + -
feeder ; fc= fish carnivore ; b= benthos feeder ; h= herbivore.
b” P P f9: b b b P b b b b fc b b b b P b f: P P b h b h b fc b b iit b :: f9: fc b fc fc b fc b P