MEPS 197:121-137 (2000)  -  doi:10.3354/meps197121

ABSTRACT: Three major size classes of the benthic metazoan communities (megafauna, macrofauna and meiofauna) were investigated simultaneously at 3 sites in the tropical Northeast Atlantic. The sites varied in their level of surface primary productivity (eutrophic, mesotrophic and oligotrophic). Results for 3 cruises in 3 seasons (Eumeli 2, winter 1991; Eumeli 3, autumn 1991; Eumeli 4, spring 1992) are given for each size class in terms of taxonomic composition, density and biomass. The benthic communities did not exhibit evidence of seasonal variation, but there were substantial differences in the quantitative structure of the metazoan communities between the 3 sites. Total metazoan density and biomass, as well as density and biomass of each size class, decreased with increasing depth and decreasing food supply, suggesting that food limitation is the major factor controlling benthic standing stocks. The comprehensive study across the 3 major benthic metazoan size classes reveals that each component responds differently to the variation in food input, leading to a variation in the quantitative structure of the benthic metazoan fauna. The largest size class, megafauna, dominated biomass when the food input was high (eutrophic site), macrofauna was predominant in intermediate conditions (mesotrophic site), and meiofauna dominated where the food input was the lowest and depth the greatest (oligotrophic site). However, within a single size group, some taxa did not follow the trend of decreasing biomass with decreasing food supply, suggesting that food availability is not the only factor governing the structure of the benthic fauna. The influence of abiotic and biotic factors likely to affect the benthic communities was analysed. Physical conditions and biological features can also play a significant role in structuring abyssal fauna.

KEY WORDS: Deep sea · Tropical Atlantic · Meiofauna · Macrofauna · Megafauna · Taxonomic composition · Density · Biomass · Environmental conditions