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 Tunne l' was used on sublittoral marine sediment substrate. Our test organism was the ascidian Microcosmus sulcatus. Particle and chlorophyll a reduction we re recorded. The correlation of seasonal fluctuations of chlorophyll a conc entrations with chlorophyll a reduction by M. sulcatus indicates the potent ial for Microcosmus to control local phytoplankton input to the subtidal ne pheloid layer. However, the relatively low density of Microcosmus at the st udy site, the nature of the sediment surface and the susceptibility of asci dians to high turbidity (i.e., high sedimentation rates of total particular matter (TPM) causing frequent periods of siphon closure and inactivity) ma kes it unlikely that M. sulcatus is an important element controlling the co mposition of the nepheloid layer on a large scale.