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Coccolithophore succession in the coastal waters of Rovinj, north-east Adriatic

Coccolithophores are unicellular calcifying eukaryotes and important primary producers in the world oceans. However, little is known about their roles in the coastal ecosystems. Main objective of this study was to determine coccolithophore diversity and species succession in the coastal waters of Rovinj. Coccolithophore flora of Rovinj and the northern Adriatic was well studied in the early 20th century by Schiller (1913, 1925) and Kamptner (1941), in those taxonomic studies they described about 50 coccolithophore species. Afterwards, species lists were produced by Revelante (1985/1986) and Viličić (2002), both of which were only based on literature data, and contained many synonyms and taxonomic inaccuracies. Moreover, there are only scarce records of diversity and ecology of coccolithophores in the Adriatic. Thus, this study also considers coccolithophore dynamics in relation to variable environmental conditions. This is particularly important in marginal seas such as the Adriatic where the small water body, with at times restricted circulation, can result in amplified responses to external changes. The research was completed over a one year period (2008–2009) every ten days in the coastal area 1 nm in front of Rovinj (45°4'40"N, 13°36'29"E) using microscopic examination, both light and electron scanning, as well as pigment analysis by HPLC. A total of 60 coccolithophore morphospecies were recorded. Dominating genus was Syracosphaera, represented by 20 species. Coccolithophores of both HET and HOL phases were present throughout the investigated period (Figure 4), while seasonality in HET/HOL phases was observed for Coronosphaera mediterranea (autum)/ HOL Calyptrolithina wettsteini (spring) and Syracosphaera pulchra (summer)/ HOL Calyptrosphaera oblonga (spring). Pigment analysis pointed to a clear domination of haptophytes in the investigated area. High concentrations of 19’-hexanoyloxyfucoxanthin were recorded throughout the year with a distinct peak in the late spring. This late spring period (March- June) was characterized by a high species diversity and higher contribution of coccolithophorids to the total phytoplankton assemblage (>60%). The typical summer coccolithophores, Rhabdosphaera clavigera and Syracosphaera pulchra, were related to high temperatures and low nitrate concentrations. Calciosolenia murrayi and Algirosphaera robusta were related to elevated nutrient concentrations, and were characteristic for the autumn assemblage. They were able to find favourable living conditions despite the abundant occurrence of diatoms and low light transmission values. Highest abundances of the species Emiliania huxleyi (106 cells L-1) were recorded in January during a monospecific bloom (92% of whole phytoplankton community). E. huxleyi was the most frequently recognized species and was related to low temperature and nutrient rich waters, present in high numbers both during winter and summer.

coccolithophores; northern Adriatic; coastal waters

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