Hessler and Jumars (1974) revisited: abyssal polychaete assemblages from the Atlantic and Pacific

Abyssal polychaete assemblages from three sites in the NE Atlantic were compared with three from the equatorial Pacific. Both sets of sites lie along perceived productivity gradients. Abundance of polychaetes was related to measures and proxies of nutrients reaching the deep-sea floor, while diversity was not consistent. Similarly, trophic groups did not show any major changes in abundance or diversity which could have been associated with changing nutrient input. Analysis of sample species richness (a diversity) indicated high species richness on a par, at similar densities, with deep-sea sites from slope regions; the main difference being that shallower sites have higher densities and thus more species overall per sample. However, our analysis indicates that an extreme number of replicates would be needed to sample adequately all the species at a site because of high species richness, intersample variability, and low densities. Comparison between sites (beta diversity) is difficult because of the need for large numbers of replicates, but preliminary results suggest that both Atlantic and Pacific assemblage composition changed over a scale of 500-1000 km. Our results indicate that the abyssal ecosystem is not one uniform habitat but is composed of many distinct regions. Overall, our diversity and trophic structure results agree with findings made by Hessler and Jumars (1974, Deep-Sea Research, 21, 185-209). (C) 1998 Elsevier Science Ltd. All rights reserved.