SCALES OF BIODIVERSITY IN ABYSSAL BENTHIC POLYCHAETES
Glover, A.
Department of Zoology, The Natural History Museum, Cromwell Rd, London SW7 5BD, England
Abyssal benthic polychaete communities were examined from four sites in the Atlantic along a latitudinal productivity gradient. This research follows directly from a study by Paterson et. al., (in press in Deep-sea Research) that highlighted the paradox of deep-sea benthic ecology: surface productivity, nutrient flux and carbon burial rate may show high latitudinal variation, but sample biodiversity does not. Sites with over two-fold differences in production and nutrient flux rates do not differ in sample biodiversity. Paterson et. al. (in press) also showed that species turnover was operating on scales of 1000+ km with sites sharing only 20-25% of species. What is causing this apparent disparity between alpha and beta diversity? It is stressed that between site comparisons are problematic as no sites have yet been fully sampled. In addition it is difficult to ascertain the relative importance of community structuring processes due to our limited understanding of polychaete reproductive biology in the abyss. However, new data from the North Atlantic seems to indicate the importance of seasonality in structuring polychaete communities. Sediments with highly seasonal food falls contain polychaetes distributed throughout the top 5 cm of sediment, while sediments that are subjected to a steady year-round 'rain' of food contain polychaetes only in the top 0-1 cm layer. There is an increased role for bioturbators in the seasonal food fall areas; burrowing and subsurface deposit feeders are able to utilise the nutrients that are not processed by the surface deposit feeders. It seems probable that differences between sites are the result of variable nutrient regimes, levels of bioturbation and physical disturbance. At the same time, a diversity is maintained by spatial and temporal patchiness in response to food falls. Further sampling effort is needed to confirm that faunal turnover is occurring on such scales in the Atlantic. Time-series data from single sites is needed to elucidate the responses of macrofauna to food fall and disturbance events.