POLYCHAETE DIVERSITY AT TROPICAL ATLANTIC DEEP-SEA SITES - ENVIRONMENTAL-EFFECTS

This study assesses how differences in nutrient flux and bottom curren ts affect the diversity and trophic structure of deep-sea polychaete c ommunities from the tropical northeast Atlantic at 20 degrees to 21 de grees N latitude. Faunal assemblages were studied from 3 sets of USNEL box cores (0.25 m(2)) taken at depths of 1700, 3100 and 4600 m. In te rms of primary productivity, the cores were taken beneath water which is eutrophic, mesotrophic and oligotrophic, respectively. Total polych aete abundance, abundance of dominant species, and faunal similarity a nd diversity were compared among the 3 sites. Polychaete abundance dec reased with increasing depth. Community structure reflected environmen tal characteristics as well as the influence of coastal upwelling. Pol ychaete diversity showed a parabolic distribution, with depth peaking at about 2000 m. Species richness observed at the eutrophic site was g enerally higher than observed at other deep-sea regions of comparable depth at temperate latitudes. This points to regional variation in pro cesses contributing to diversity patterns of deep fauna. We suggest th at the diversity pattern observed results from non-equilibrial interac tions between production and disturbance in the form of current energy and bioturbation. Diversity patterns observed in the EUMELI sites see m best explained by the intermediate productivity theory. The rate of production encountered at the eutrophic site may overcome much of the impact of physical and biological disturbances, favouring a diverse sp ecies assemblage.