An in-situ study on the influence of ascidian suspension feeding on the subtidal nepheloid layer in the northern Adriatic Sea

In order to evaluate the effect of epibenthic suspension-feeding organisms on nepheloid-layer processes, a novel flow-through 'Benthic Ecosystem Tunnel' was used on sublittoral marine sediment substrate. Our test organism was the ascidian Microcosmus sulcatus. Particle and chlorophyll a reduction were recorded. The correlation of seasonal fluctuations of chlorophyll a concentrations with chlorophyll a reduction by M. sulcatus indicates the potential for Microcosmus to control local phytoplankton input to the subtidal nepheloid layer. However, the relatively low density of Microcosmus at the study site, the nature of the sediment surface and the susceptibility of ascidians to high turbidity (i.e., high sedimentation rates of total particular matter (TPM) causing frequent periods of siphon closure and inactivity) makes it unlikely that M. sulcatus is an important element controlling the composition of the nepheloid layer on a large scale.