Dinoflagellate cyst production at a coastal Mediterranean site

Abstract

To assess the diversity and seasonality of dinoflagellate cyst production, surface sediment and trap samples were studied in the Gulf of Naples (Mediterranean Sea). A total of 59 different cyst morphotypes were recorded. At the stations within the 70 m isobath, sediment assemblages were dominated by calcareous Peridiniales (66-79%), while at the deepest stations non-calcareous Peridiniales attained the highest percentages (40-49%). The sediment trap sampling, carried out fortnightly over two annual cycles, revealed high production rates (up to 1.7 x 106 cysts m-2 day-1) from spring to late autumn of both years, with a distinct seasonal production pattern. Although rather similar in species composition, the total cyst flux differed markedly between the 2 years (1.26 and 0.55 x 108 cysts m-2 year-1, respectively). Species-specific production patterns were observed: some species formed cysts over several months, others in restricted periods of the year. Cyst-forming species constituted a small part of the planktonic dinoflagellate populations recorded in the area. A coupling between the trap material and surface water plankton was observed for calcareous Peridiniales. This sampling approach allowed the detection of some species never recorded before in the gulf, including two potentially toxic species: Alexandrium andersoni and Gymnodinium catenatum-like species.