DEMERSAL FISH ASSEMBLAGES ALONG THE PACIFIC COAST OF COSTA-RICA - A QUANTITATIVE AND MULTIVARIATE ASSESSMENT BASED ON THE VICTOR-HENSEN-COSTA-RICA-EXPEDITION (1993 1994)/

During two cruise legs with the RV Victor Hensen (December 1993, Febru ary 1994), the demersal fish assemblages of the Golfo de Nicoya (GN), Bahia Coronado - Sierpe Terraba (ST) and Golfo Dulce (GD) areas were a ssessed from nearshore (similar to 20 m) to shelf edge (similar to 200 m) waters. 44 Beam- and 29 otter trawl collections were made on an ar ea of 2 119 405 m(2), yielding a total of 242 species of fish. Despite the lower number of samples taken, more species were collected by the otter trawl (189 compared to 160), due to a wider area swept. As reve aled by the species-area curve and a lognormal - curve constructed fro m the pooled (log) abundance data the fish assemblage appeared as well sampled and a theoretical species richness (SR) of similar to 306 was estimated for the whole area. Mean species number per collection and mean biomass per area were much lower in the GD - area (9.3 species, 0 .36g/m(2)) compared to the ST (15.4, 0.81g/m(2)) and GN (17.3, 0.74 g/ m(2)) areas, indicating a depauperate fish assemblage in the former. L owest species numbers and biomass were found in the central deep part of GD with increasing values towards the sill area at the opening of t he gulf and towards the shallow stations above the thermocline. Averag e biomass was an order of magnitude higher in the interior part of GN compared to the other areas with values up to 18.1 g/m(2). Based on re sults of a multivariate analysis of the collections, the GN area can b e divided into (1) an interior shallow area above the thermocline (<50 m) characterized by scianids, sea catfishes, stingrays, flatfishes, s ea robins, (2) an outer part (>100 m) characterized by cods, scorpionf ishes, gobies, cutlassfishes, serranids, anglerfishes and flatfishes a nd (3) a transition zone of the central and lateral parts with a mixed species assemblage with carangids, pufferfish, snappers, several flat fish species and the lizardfish as common elements. Characteristic for the deep basin of GD were small species of the genera Cynoscion and P orichthys. These occurred in low densities, suggesting a reduced carry ing capacity of this deep basin for fish biomass in terms of food and oxygen. Species occurring at the shallow stations of GD are also found at a similar depth in the other areas, but many species are missing, namely ariids and many scianids found in the GN area. The species asse mblage of the ST area resembles that of GN. Ariids, however, are missi ng here too. Biotic station parameters like species richness, biomass, abundance and production were not significantly correlated with abiot ic parameters (temperature, oxygen, nutrients) suggesting that other h abitat factors not evaluated in this study like habitat heterogeneity, distance to the open ocean, current regime and food availability prob ably are important factors for the structure of the fish assemblage.