Vertical distribution of metazoan macrofauna within the sediment at four sites with contrasting food supply in the deep Arabian Sea

The regional variability of abundance, biomass and vertical distribution of metazoan macrofauna was investigated at four sites in the deep Arabian Sea (water depth 3190-4420 m) that differ with respect to the amount and seasonal pattern of vertical particle flux. Mean density of total macrofauna ranged from 300 ind/m(-2) in the southern to 2100 ind/m(-2) in the western Arabian Sea. At all stations, Crustacea were the most numerically abundant taxon, followed by Polychaeta. Total macrofaunal biomass ranged from 21 (southern A. S.) - 106 (western A. S.) mg C/m(2). Although both parameters thus mirror the gradient in food input between the stations, no significant correlation was found between vertical flux and abundance or biomass of macrofauna, and biomass values were much lower than expected. Instead, a significant correlation with the CPE content of the surficial sediment was found and CPE thus might be a better proxy for the input of food available for macrofaunal organisms. Two extremes in the vertical zonation pattern of macrofauna within the sediment could be described that are possibly linked to the varying degree of seasonality in food supply: in the western, northern and central Arabian Sea vertical POC flux is tightly coupled to monsoon dynamics and depicts a strong seasonality. Here, high macrofaunal density and deep-dwelling communities were encountered. In the southern Arabian Sea, where total POC flux is much lower and does not depict a large seasonal amplitude, a strong concentration of organisms at the sediment surface was found. The implications of this vertical distribution patterns for biological sediment mixing are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.