In situ macrofaunal respiration rates and their importance for benthic carbon mineralization on the northwestern Black Sea shelf

Benthic fauna assemblages and organic carbon mineralization processes were studied in the northwestern Black Sea along a transect from the well-oxygenated shelf to the (deep) anoxic basin. Bivalves dominated the coenoses at the three oxygenated stations, but with decreasing macrofaunal biomass at increasing water depth. The previously well-described zonation of macrofaunal communities for the northwestern shelf of the Black Sea was also found in this study (Mytilus galloprovincialis coenosis at Station 1 (62 m), Modiolus phaseolinus coenosis at Station 2 (77 m) and 3 (100 m)). The highest meiofauna density was found at the transition from oxic to anoxic bottom waters (Station 4, 130 m, < 5 muM O-2). Reduced predation and sufficient food supply are suggested to be of importance at that site. The weight-specific fauna-mediated respiration rate of the mussel community was independent of water depth and always around 14 nmol O-2 mg ww(-1) d(-1). Thus indicating that the mussel communities on the northwestern Black Sea shelf do not adapt their consumption rates to the decreasing bottom water oxygen concentrations. The contribution of the macrofaunal assembly to the overall mineralization of organic carbon at the oxic stations was high, reaching a maximum of 70% at the shallowest investigated site