Coccolithophore diversity in open waters of the middle Adriatic Sea in pre- and post-winter periods

This research describes coccolithophore assemblages in open middle Adriatic waters, in relation to in-situ environmental parameters measured during the pre-winter (December 2015) and post-winter (April 2016) periods. The study is part of a larger campaign focused on characterising the marine environment before and after the winter dense water formation in the Adriatic. Coccolithophores represented the major component of the phytoplankton community, prevailing over diatoms during the entire investigation period, while their abundance in December was significantly lower than in April. Regarding coccolithophore diversity, 76 taxa were recorded, with the majority being heterococcolithophores (HET). A greater incidence of holococcolithophores (HOL) were recorded in April 2016. Emiliania huxleyi was predominant in the assemblages. During the entire study period, eight coccolithophore species were observed in two life stages (HET and HOL phase): Acanthoica quattrospina, Calcidiscus leptoporus, Coronosphaera mediterranea, Syracosphaera anthos, Syracosphaera pulchra, Syracosphaera bannockii, Syracosphaera histrica and Syracosphaera molischii. Among these, A. quattrospina, S. histrica, S. molischii and S. pulchra appeared in a rare combination HET/HOL phase. The 810 ENV analysis indicated that the heterococcolithophore community is best related to pH value, while the holococcolithophore community is significantly affected by more than one environmental variable.