Differential responses of bacteria, meiofauna and macrofauna in a shelf area (Ligurian Sea, NW Mediterranean): role of food availability

Density and biomass of bacteria, meio- and macrofauna were examined along a transect of eight stations (5-135 m depth) facing the estuary of the river Entella (Ligurian Sea) during summer 1990. Sediment samples were collected to determine organic detritus composition (total organic matter: lipid, pr otein and carbohydrate concentrations) and microphytobenthic biomass las ch lorophyll-a). Synoptic water samples were collected to determine the quanti ty and the quality of suspended matter (total suspended matter, particulate lipids, proteins, carbohydrates and chloroplastic pigments). Particulate o rganic matter in the surface water decreased from the coast towards the ope n sea both in quality and quantity. By contrast, the organic-matter concent ration in the sediment increased with water depth. Quantity and biochemical composition of suspended and sedimentary organic matter affected the distr ibution of all the benthic assemblages. Bacteria appeared to be controlled by different parameters at different depths: generally they appeared to dep end upon sediment particle surface and the quantity of organic matter, but when metazoan (particularly meiofauna) densities were high, grazing pressur e might also exert a control on their abundance. The distribution of meio- and macrofauna along the continental shelf of the oligotrophic Ligurian Sea appears to depend more upon the quality of organic matter than on its quan tity. (C) 1999 Elsevier Science B.V. All rights reserved.