Macroinfauna of a tropical fjord-like embayment: Golfo Dulce, Costa Rica

Abstract

A total of 136 sediment subsamples was analyzed (500 μm mesh screen) for benthic invertebrates from 26 box corer samples collected by the RV Victor Hensen (Dec. 7, 8, 9, 1993), at nine stations ranging in depth from 43 to 200 m in the Golfo Dulce embayment. Pacific coast of Costa Rica. A total of 1690 individuals and 69 species was found; polychaetes dominated the fauna in terms of number of individuals (1506) and species (47). Eight species of polychaetes accounted for 73% of the total number of individuals: Prionospio (Minuspio) sp. A (19.53%) Aricidea (Acesta) catherinae (13.31%), Levinsenia gracilis (11.00%), Aphelochaeta longisetosa (10.18%), Paraprionospio pinnata (6.63%) Cossura brunnea (5.27%), Mediomastus californiensis (3.61%), and Scoletoma platylobata (3.43%). No organisms were collected at the two deepest statiQns (200 m) located inside Golfo Dulce; however, a diverse fauna was found at similar depths II the embayment mouth and in waters shallower than 100 m inside Golfo Dulce. The station located at the sill (75 m) was the most diverse (37 species). The species composition of the fauna found during this study has little resemblance to that reported for Golfo Dulce in 1976. Diversity (H') and Evenness (J'), however, were similar in both surveys. The results of cluster analyses performed on the 1976 and 1993 data sets yielded two main groups of stations. One group was made of the stations located at the mouth and shelf, while another group included those located inside Golfo Dulce. The fauna of the sill sediments may represent a transition zone between the environments characteristic of the entrance to Golfo Dulce and those inside the embayment. The fluctuating bottom conditions of hypoxia-anoxia characteristic of most of Golfo Dulce, in addition to the likely impact of strong El Niño in the marine ecosystems, might be the causes for drastic shifts in species composition and abundance. Golfo Dulce is still a relatively unpolluted embayment, but an Integrated Area Management Plan is urgently needed. This paper, in addition to those already published resulting from the RV Victor Hensen Expedition, are a step towards this goal.