Diversity of the Ichthyofauna of Estuaries in Southeastern Trinidad

Diversity of the Ichthyofauna of Estuaries in Southeastern Trinidad W. G. Rostant1, R. S. Mohammed2, F. B. Lucas2 and P. Badal3 1. Circular Road, St. Augustine, Trinidad and Tobago 2. Department of Life Sciences, University of the West Indies, St. Augustine, Trinidad and Tobago 3. Priest Hill Road, St. Joseph, Trinidad and Tobago ABSTRACT Estuaries are highly productive aquatic systems. Five rivers in Guayaguayare Bay were sampled for ish by seining. During the survey, 25 species in 21 families representing eight orders were collected or observed. The most abundant species, Mugil curema, accounted for 56% of total catch. For the majority of species encountered, the size-frequency distributions revealed populations comprised largely of subadults and juveniles. Dissimilarity of inventories between sites may be related to a combination of biotic and abiotic factors. It is proposed that each species is maintained over the entire coastline by a series of incompletely independent populations and that these estuaries collectively represent one large metacommunity. Key words: estuaries, ish fauna, metacommunity. INTRODUCTION with the density of most early life and many juvenile stages An estuary is a semi-enclosed coastal body of water being positively related to hydrological events (Morais and which has a free connection with the open sea, and within Morais 1994; Sylvie et al. 1999). which sea water is measurably diluted by fresh water deIn traversing the coastline bounded by the Moruga rived from land drainage (Pritchard 1967). Estuaries are River to the south and the Ortoire River to the east, one often associated with high rates of biological productivencounters the discharge points of many small to moderate ity due primarily to the in situ photosynthetic activity of drainages of quite similar overall topography. All of these phytoplankton, submerged vascular plants, periphyton, streams are of rather gradual gradient, and drain mainly benthic algae, tidal marsh detritus, and land runoff, in lat land under a varied mosaic of vegetation types from decreasing order (Correll 1978). The nature of estuaries forest to cultivation and coastal shrub, mangrove and is such that they are able to trap productive bottom sedistrand. None achieve the catchment area of the formerments carried in rivers and high levels of nutrients from mentioned rivers. land runoff (Correll 1978). Fish communities that are located in estuaries are important to diverse groups such as scientiic community, natural resource managers, and user groups. Fish communities that occur in estuarine environments can have their origin in marine or freshwater habitats and it is generally believed that the ish found in these areas are dominated by species that spawn at sea (McHugh 1967 in Berlatta-Bergana et al. 2002). Estuarine areas are utilized by the juveniles of marine species as it provides a safer environment for vulnerable larval stages. Hydrological events can play an important Fig. 1. Map of southeastern Trinidad showing ive principal sampling sites. role in the temporal variation in densities of many ish taxa 31 Living World, J. Trinidad and Tobago Field Naturalists’ Club, 2007 32 Because of their low proile, low is rather slow and the marine inluences of tide and salinity tend to extend far inland resulting in well-developed estuarine habitats of untested, but purported high ecological importance. The present baseline study is located at this interface between marine and freshwater systems speciically in the vicinity of Guayaguayare Bay and Pt. Galeota. Five river mouths (Fig.1) were sampled including those of the (1) St. Hilaire, (2) Pilote and (3) Lizard Rivers on the south coast. Two other unnamed streams were also investigated including (4) Stream A, on the south coast approximately one km east of Lizard; and (5) Stream B, located north of the Briko Air Services helipad on the east coast side of Pt. Galeota. Table 1 gives the UTM coordinates of these ive sites along with the times and dates of sampling. Site Descriptions 1. St. Hilaire River formed an almost enclosed, mangrove-lined lagoon during the rising tide. Sea conditions were fairly rough with the breakers bringing a considerable amount of sea-transported woody and other vegetative debris into the river via the 3 m wide channel. Upstream of this shallow, narrow channel the river attained a wider, deeper proile (approximately 10 m wide and up to 1.5 m deep). 2. Pilote River was the widest and deepest of all sites sampled. The tide was rising and, with fairly rough sea conditions, there was a strong landward tidal current coupled with considerable wave action. Floating mats of vegetation were quite commonly observed entering through the comparatively narrow beach channel (about 5 m wide) into the much wider (>25 m at widest point), deeper (>2 m at deepest point) sandy lagoon downstream of the bridge. All seining was done downstream of the bridge. Upstream of the bridge the river narrowed slightly and was lined with mangrove. 3. Lizard River was approximately 15 m wide and 1.5 m deep at the bridge. Mud/sand lats obtained on either side of the channel immediately upstream of the bridge and at the time of sampling (falling tide) turbid water could be seen entering the main river channel as the surrounding mangrove wetland drained. Downstream of the bridge the river narrowed to about 5 m and gradually became shallower as it lowed over the low-proile beach towards the sea. 4. The irst unnamed river, Stream A, was accessed via a trail at the side of the road opposite the “Sit and Chat” Bar. At the time of sampling, the river mouth was almost completely blocked by a sand bar except for a very narrow (~1 m), shallow (~ 5 cm) channel. The actual depth was roughly 1 m within the sampling area. The surrounding vegetation was mainly secondary fringing forest, mangrove and Bactris palms. 5. The second unknown river, Stream B, was accessed via Pt. Galeota. From the car park near Briko Air Services helipad, the mouth of the river was accessed by walking to the beach and then north along the coast. This site was sampled at low tide and was almost completely blocked by a sand bar. At its widest point, the river was about 12 m wide and 1.5 m deep and lined with mangrove. There was no detectable low. METHODS All sites were sampled using primarily a 10 m long river seine of mesh size ~ 0.5 cm. Two reaches of approximately 10 m in length were seined by pulling with the direction of the current (which varied between ebb and low among the sites sampled) or toward the sandbank on the seaward end where there was no discernible low. Further sampling was done using a long-handled landing net (mesh approximately 0.5 cm) in microhabitats not suited to seining, namely channel margins with undercut banks and amongst submerged and emergent vegetation. All ish were counted and measured. In keeping with standard practice, total length (TL) was recorded. Easily identiied species were counted in situ and returned live to the water. However, representative specimens of most species had to be kept for subsequent identiication. These individuals were kept on ice and later preserved, using 70% ethanol. Subsequently they were identiied using keys and descriptions, FAO (1978), Froese and Pauly (2006), Eshemeyer (1998), Perez-Farfante and Kensley (1997). To incorporate a measure of evenness into the analysis Table 1. List of sampling sites, times and coordinates. Site # Name Date sampled Sample time Tide GPS (UTM 20P) 1 St. Hilaire 8 Sep 06 1450 - 1540 rising 713093 E 1120180 N 2 Pilote 8 Sep 06 1320 - 1430 rising 713548 E 1120609 N 3 Lizard 8 Sep 06 0820 - 1000 falling 716404 E 1122843 N 4 Stream A 8 Sep 06 1010 - 1100 low 717405 E 1123109 N 5 Stream B 9 Sep 06 1000 - 1100 low 719497 E 1123382 N Fish Fauna of Guayaguayare Bay of diversity for each site, Shannon’s diversity index was calculated using the following formula: Sciades herzbergii 45 H = – ∑ pi in pi s 40 i=1 35 30 Frequency where S = total number of species in the community; pi = the proportion of S made up by the ith species. 33 25 20 15 To get an understanding of site similarity, a matrix based on fourth10 root transformed abundance was 5 constructed using the Bray-Curtis measure (Bray and Curtis 1957). 0 <2 2-4 4-6 6-8 8 - 10 10 - 12 12 - 14 14 - 16 16 - 18 18 - 20 >20 This and the subsequent cluster Size class (cm) analysis (using group-average linkage) of sites was done using the Fig. 2. Frequency-size distribution for all Sciades herzbergii caught at sampling sites. PRIMER 5 software package, an updated windows-based version of PRIMER (Clarke and sp., Centropomus ensifurus, Polydactylus virginicus, MenWarwick 1994). ticirrhus saxatilis and Trinectes inscriptus). The remaining species were either recorded at only RESULTS one sample site (15) or subsequently observed in and During the survey, 25 species in 21 families representaround nearby estuarine habitats but not collected at the ing eight orders were collected or observed (Table 2). Of ive principal sampling sites (the carangid ish Trachinotus these, only 9 species were found at more than one sample goodei). site. One species, Selanaspis herzbergii, was found at all Site #4 had the highest species richness (12) and ive sample sites while two others (Atherinella sp. and overall abundance (307 specimens, see Appendix 1) with Mugil curema) were found at four sites. Six species were the other sites having 6 to 9 species each and much lower found at two sites (Trachinotus carolinus, Hyperoglyphe overall abundance (67 - 225). Conversely, site # 4 scored Table 2. List of species collected /observed at ive principal sampling sites and with general collecting. Order Atheriniformes Beloniformes Clupeiformes Cyprinodontiformes Elopiformes Perciformes Family Atherinopsidae Hemiramphidae Pristigasteridae Anablepidae Poeciliidae Elopidae Megalopidae Carangidae Centrolophidae Centropomidae Gobiidae Haemulidae Lobotidae Lutjanidae Pleuronectiformes Siluriformes Mugilidae Polynemidae Sciaenidae Trichiuridae Achiridae Paralichthydae Ariidae Species Atherinella sp. Hyporhamphus unifasciatus Odontognathus compressus Anableps anableps Micropoecilia picta Elops saurus Megalops atlanticus Trachinotus goodei Trachinotus carolinus Caranx crysos Hyperoglyphe sp. Centropomus pectinatus Centropomus ensifurus Evorthodus lyricus Haemulon bonariense Lobotes surinamensis Lutjanus griseus Lutjanus sp. Mugil curema Polydactylus virginicus Menticirrhus saxatilis Trichiurus lepturus Trinectes inscriptus Cyclopsetta chittendeni Selanaspis herzbergii Common name baitfish, silverside half beak, balaju herring four-eyed fish swamp guppy, millions ladyfish, banane grand-écaille, tarpon palometa, pompano pompano carangue ruff snook snook goby grunt leaf fish (marine) grey snapper snappers white mullet thread fin croaker cutlassfish flatfish left eyed flounder catfish Authority 1 l (Ranzani 1842) Meek & Hildebrand (1923) (Linnaeus 1758) (Regan 1913) Linnaeus (1766) Valenciennes (1847) Jordan & Evermann (1896) (Linnaeus 1766) (Mitchill 1815) 2 l l l Presence at site 3 4 l l 5 General l l l l l l l l l l l l l l Poey (1860) Poey (1860) (Girard 1858) Cuvier (1830) (Bloch 1790) (Linnaeus 1758) l l l l l l l l l Valenciennes (1836) (Linnaeus 1758) (Bloch & Schneider 1801) Linnaeus (1758) (Gosse 1851) Bean (1895) (Bloch 1794) l l l l l l l l Total species H 6 1.161 l l 9 1.401 l 7 1.350 l l l l 12 1.018 6 1.084 4 Living World, J. Trinidad and Tobago Field Naturalists’ Club, 2007 34 Atherinella sp. 100 90 80 Frequency 70 60 50 40 30 20 10 0 <2 2-4 4-6 6-8 8 - 10 10 - 12 12 - 14 14 - 16 16 - 18 18 - 20 Size class (cm) Fig. 3. Frequency-size distribution for all Atherinella sp. caught at sampling sites. >20 include the ubiquitous S. herzbergii (80 individuals, 9% of total catch) and Menticirrhus saxatilis (two sites, 44 individuals, 5% of total catch). In the cluster analysis the Lizard River site separates out irst at about 28% similarity (Figure 5). Of the remaining sites, Stream B separates next at about 41%. This is followed by Pilote, which is 53% similar to the remaining two sites. St. Hilaire and Stream A are the two most similar sites at about 61%. All species caught have been recorded from inshore or brackish waters within the Western Central Atlantic and Caribbean ishing area (Froese and Pauly 2006) with no purely freshwater species represented. Important commercial and artisanal isheries are based on many of the ish species caught. Frequency the lowest Shannon index (1.018), with site #2 scoring the highest (1.401). DISCUSSION Sites #1 and #5 each had only one unique species The fact that these catchment areas are only very (only caught at that one site) while all other sites had three sparsely inhabited suggests minimal land-based anthropoor four unique species. These accounted for 17%, 44%, genic impact on the estuarine communities. Assuming this 57%, 25%, 44% and 17% of the inventories of sites #1 to be true, and that marine based pollution/disturbance is - 5 respectively. not a major factor, the inventories produced herein would The only species common to all sites, Selanaspis be representative of the natural communities that exist in herzbergii, had an approximately normal size distribution (Figure 2) with a mode at 8-10 cm. Of Mugil curema the two other common species 180 (caught at minimum of 4 sites) 160 Atherinella sp. (with a modal size of 8-10 cm, see Figure 3) 140 has a continuous size distribution; while there is a distinctly 120 disjunct distribution for Mugil 100 curema (Figure 4). This last species was not only 80 very common, but also the most 60 abundant with 475 individuals caught (56% of total catch) and 40 was the most dominant species 20 where present. Atherinella sp. was the most abundant species at 0 site #3 and the second most abun<2 2 - 4 4 - 6 6 - 8 8 - 10 10 - 12 12 - 14 14 - 16 16 - 18 18 - 20 >20 dant overall with 162 individuSize class (cm) als caught (19% of total catch). The next most abundant species Fig. 4. Frequency-size distribution for all Mugil curema caught at sampling sites. Fish Fauna of Guayaguayare Bay 35 coastal estuaries of the southeast coast. not always be, as tidal regimes change over each month, For the majority of species encountered, the sizesea conditions and/or high rainfall can breach sand bars. frequency distributions revealed populations comprised High rainfall may also signiicantly alter salinities within largely of subadults and juveniles (comparing size ranges the lagoon. caught to maximum sizes listed in Froese and Pauly Commonly, daily physical and chemical variation in {2006}). Of the two large M. curema captured at site #2 estuaries produces a particularly demanding environment (Pilote), it was discovered that one of two individuals was a that has profound effects on biological communities. The mature female that was gravid. These observations indicate irst and most intuitive effect is that individual species the importance of these habitats as nurseries, where some must either have a wide range of tolerances or else undergo marine species spawn and undergo early development. For signiicant daily migration to maintain themselves within other species, juveniles may move between these habitats suitable niche-space. Even for the species that have wide and the sandy nearshore environment depending on the tolerance ranges, e.g. the euryhaline Selanaspis herzbergii, tide and availability of food. localized populations may undergo quite drastic luctuaWhile the total species count was fairly impressive, tions as they are exposed to varying immigration, emigraeach individual site was less so, with the majority of tion and extirpation of populations of competitors, prey and species restricted to one site. Mugil curema proved to be predators. It is therefore not surprising that the inventories quite dominant overall and at each individual site. In fact, at the ive sites are so different from one another. the second highest evenness (as shown by the Shannon The importance of each small estuarine habitat does diversity index), occured at site #3 (Lizard) where this not necessarily lie in this perceived uniqueness. In fact, if species was not caught. The presence of the large predathese sites were sampled over a time series that incorpotory Trichiurus lepturus at this site may account for the rated season it might be expected that the integrated lists absence of the highly mobile M. curema. On inspection would be quite similar. Rather, one should view these of the gut contents of the predator, remains of several M. small habitats within a larger framework in which local curema were found, lending credence to this explanation. communities are linked by dispersal of individuals of their It is the unique presence of this predator and absence of constituent species i.e. the metacommunity (Holyoak et the prey species in the samples collected at this site that al. 2005). largely account for its highest dissimilarity in the cluster Thus while localized communities may exhibit quite analysis. variable dynamics, the tendency is for the metacommunity The populations found within each small estuarine to be quite stable and sustained by the combined effects habitat are more than likely connected via dispersal esof its many constituent communities. If this interconpecially since the majority of the species encountered are nectedness on the large scale (over the entire coastline either primarily marine or frequently move between the or nearshore ecosystem) is considered, the importance marine and estuarine environment. As such, each species of each small part (community) in stabilizing the whole is maintained over the entire coastline Guayaguayare by a series of incompletely independent populations, which together can be 4. Stream A termed metapopulations (Levin 1969; Hanski and Simberloff 1997; Hanski 1997; Harrison and Taylor 1997; Cronin 1. St. Hilaire 2003). Small estuarine habitats are very dy2. Pilote namic in physical and chemical nature, with current, depth, salinity, turbidity 5. Stream B and dissolved oxygen regularly varying on a daily basis. The fact that site #4 (Stream A) had the highest species 3. Lizard richness may be a result of the com20 40 60 80 100 paratively closed nature of the lagoon found and the small size of the catchment Bray-Curtis Similarity (%) (the stream does not even appear on the map) as these would presumably result Fig. 5. Dendrogram showing hierarchical clustering of sampling sites using Bray-Curtis simiin a more stable environment. This may larity (%). 36 Living World, J. Trinidad and Tobago Field Naturalists’ Club, 2007 (metacommunity) cannot be discounted. ACKNOWLEDGEMENTS We would like to thank Karl Ramjohn and Fern Gemma Lucas for help in the ieldwork for this paper; and Carol Ramjohn in the preparation of this paper. REFERENCES Barletta-Bergana, A., Barlettab, M. and Saint-Paula, U. 2002. Structure and seasonal dynamics of larval ish in the Caete´ River estuary in north Brazil. Estuarine, Coastal and Shelf Science, 54: 193-206. Bray, J. R. and Curtis, J. T. 1957. An ordination of the upland forest communities of Southern Wisconsin. Ecol. Monogr., 27: 325-349. Clarke, K. R. and Warwick, R. M. 1994. Change in Marine Communities: An Approach to Statistical Analysis and Interpretation. Natural Environment Research Council, Plymouth Marine Laboratory, Plymouth. Correll, D. L. 1978. Estuarine productivity. BioScience, 28, (10): 646-650. Cronin, J. T. 2003. Movement and spatial population structure of a Prairie Planthopper. Ecology, 84: 1179-1188. Eschmeyer, W. N. 1998. Catalog of Fishes (Vols. I-III). Special Publication No.1 of the Center for Biodiversity Research and Information. California Academy of Sciences, San Francisco. 2905 p. FAO. 1978. FAO species identification sheets for fishery purposes, Western Central Atlantic (Fishing area 31), ed. W. Fischer. Rome: FAO. Froese, R. and Pauly, D. Editors. 2006. Fish Base. World Wide Web electronic publication. www.ishbase.org, version (07/2006). Hanski, I. 1997. Metapopulation dynamics: from concepts and observations to predictive models. pp. 69-91. In Ilkka A. Hanski and Michael E. Gilpin, eds. Metapopulation Biology. San Diego, California: Academic Press. Hanski, I. and Simberloff, D. 1997. The metapopulation approach, its history, conceptual domain, and application to conservation. pp. 5-26. In I. A. Hanski and M. Gilpin, eds. Metapopulation Biology: Ecology, Genetics and Evolution. San Diego, CA: Academic Press. Harrison, S. and Taylor, A. D. 1997. Empirical Evidence for Metapopulation Dynamics. In I. A. Hanski and M. Gilpin, eds. Metapopulation Biology: Ecology, Genetics and Evolution. Academic Press, San Diego, CA. Holyoak, M., Leibold, M. A., Mouquet, N., Holt, R. and Hoopes, M. F. 2005. Metacommunities: a framework for large-scale community ecology. pp 307-330. In M. Holyoak, M. A. Leibold and R. D. Holt, eds. Metacommunities: Spatial Dynamics and Ecological Communities Chicago, University of Chicago Press. Levins, R. 1969. Some demographic and genetic consequences of environmental heterogeneity for biological control. 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Caranx crysos Menticirrhus saxatilis Mugil curema 40 60 Polydactylus virginicus Selanaspis herzbergii Atherinella sp. Centropomus ensiferus Cyclopsetta chittendeni 1 Hyperoglyphe sp. 4 Hyporhamphus unifasciatus Lobotes surinamensis Mugil curema 20 40 Odontognathus compressus 1 Selanaspis herzbergii Atherinella sp. Centropomus pectinatus Haemulon bonariense Lutjanus griseus Micropoecilia picta 3 Selanaspis herzbergii Trichiurus lepturus Atherinella sp. Centropomus ensiferus 2 1 Elops saurus Evorthodus lyricus Hyperoglyphe sp. 4 Megalops atlanticus Menticirrhus saxatilis Mugil curema 2 Polydactylus virginicus Selanaspis herzbergii 4 Trachinotus carolinus Trinectes inscriptus 1 Anableps anableps Lutjanus sp. 20 Mugil curema 40 20 Selanaspis herzbergii Trachinotus carolinus Trinectes inscriptus 1 Totals 130 134 4-6 Totals 6 - 8 8 - 10 10 - 12 12 - 14 14 - 16 16 - 18 18 - 20 >20 4 37 8 14 2 1 1 1 1 12 1 17 1 1 8 2 1 38 2 1 1 63 1 8 120 3 30 1 2 1 2 2 3 24 6 5 5 1 1 1 4 2 12 1 8 1 1 1 3 1 2 1 6 1 1 1 6 1 12 16 168 2 3 1 39 18 1 2 1 1 4 8 3 70 133 239 5 2 67 3 13 148 34 13 1 2 3 13 1 67 1 6 4 1 36 228 2 9 1 1 2 20 60 15 1 1 1 26 225 13 5 2 8 for site 50 3 1 4 5 2 4 by species 62 18 8 1 5 846 307 99 846