The role of the diatom Cylindrotheca closterium in a mucilage event in the northern Adriatic Sea:: coupling with high salinity water intrusions

The temporal and spatial distribution of mucilaginous aggregates, during the mucilage event of 2002 in the northern Adriatic, was studied in relation to waters of different salinity considering the aggregate's age and proportion of Cylindrotheca closterium in its microphytoplankton community. The results showed that this epipelic diatom is a dominating species in the microphytoplankton community of freshly formed aggregates, in spite of its negligible abundance in the water column. The appearance and distribution of these aggregates in the water column was associated with water of higher salinity. The same pattern was observed in the summer of 2001, when a shorter and limited mucilage event occurred. These results suggest the importance of oligotrophic high salinity water intrusions from the central Adriatic for a selective accumulation of C. closterium cells. Coupling between the increased number and minimum growth state of C. closterium-accumulated cells might result in a hyperproduction of its own mucilage in these accumulation zones formed under the influence of high salinity water intrusions. In contrast, in the upper lower salinity water layers, under the influence of a freshwater input, the phytoplankton community of the freshly formed aggregates was similar to that of the surrounding water.