Oceanographic cruises were carried out monthly from June 1999 to July 2002 to follow the mucilage formation process in the 14 Northern Adriatic Sea. Results show that in correspondence with these events the dinoflagellate Gonyaulax fragilis (Schu ̈ tt) Kofoid 15 was observed both in the water column and within mucilage aggregates. In the water column, increasing abundances were observed 16 from May until July, with values never exceeding 8500 cells l1. Much higher densities were observed within superficial 17 gelatinous aggregates (22800–3400000 cells l1). In mucilage samples, a large number of decomposing cells were present, 18 together with abundant alive cells, enveloped in exudates. G. fragilis isolated from mucilage samples was cultured in three different 19 culture media; it was characterized by a low growth rate but it produced a high amount of polysaccharides.
