Benthic activity in sediments of the northwestern Adriatic Sea: sediment oxygen consumption, macro- and meiofauna dynamics

Benthic activity was examined at three stations (18 m water depth) in the northwestern Adriatic Sea. Carbon mineralisation rates, as based on sediment oxygen consumption rates, ranged from 54 to 89 g C m(-2) y(-1). The relatively high carbon mineralisation rates, large macrofaunal biomass (9 to 16 g C m(-2)) and macrofaunal production (11 to 19 g C m(-2) y(-1)) provide evidence of high organic-matter input and intense benthic-pelagic coupling. This is further supported by the high dominance of the suspension-feeding bivalve Corbula gibba, which accounts for 52 to 63% of the total annual macrofaunal biomass production. Although the infaunal distribution of total macrofauna showed a sharp decline in densities and biomass with depth into the sediment, different patterns within the dominant taxa were observed. Whilst the bivalve Corbula gibba and the amphipod Ampelisca sp. were restricted to the surface layer, other species such as the dominant bivalve Mysella sp. and the gastropod Hyala sp. were not confined to a specific depth level and the majority of the populations occurred deeper than 5 cm into the sediment. Bioturbation, based on the occurrence of macrofauna, extended to at least 20 cm. Nematodes and foraminifera together formed 80 to 90% of the meiofaunal community in the upper 5 cm of the sediment. Annual mean densities ranged from 3.40 to 6.07 x 10(6) ind. m(-2). Maximum abundance of meiofauna was not encountered at the station where maximum macrofaunal activity was recorded, and this could reflect the negative effect of biological interaction on meiofaunal densities in areas that have a high food supply. [KEYWORDS: northwestern Adriatic Sea; eutrophication; sediment oxygen consumption; carbon flux; benthic-pelagic coupling; bioturbation; macrofauna; meiofauna; biotic interactions Long-term eutrophication; northeastern north-sea; east china sea; continental-shelf; marine-sediments; organic-matter; respiration rates; margin sediments; nutrient fluxes; amazon shelf]