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Bloom of coccolithophore Syracosphaera halldalii in the Middle Adriatic estuary

The analysis of the phytoplankton community in the Krka River estuary (the middle Adriatic Sea) revealed the increased abundance of coccolithophores in the phytoplankton community in August 2017 (5, 7x105 cells L-1) and October 2017 (to 2, 3 x106 cells L-1), dominating over usually prevailing diatoms. Analyzing samples with SEM, we found that coccolithophore Syracosphaera halldalii was occurring almost in monospecific bloom reaching densities up to 2.5x106 cells L-1. Bloom of S. halldalii was observed in extremely variable environmental conditions. In the upper two layers of the water column, high fluctuation in salinity was recorded ; from 38.8 to 14.3. The temperature varied from the highest 24.0 °C to the lowest 16.4 °C, and during the entire study period, high variability in nutrients input was also observed. Coccolithophore S. halldalii consists of only the heterococcolith life-cycle phase. Cell morphology was analyzed using SEM, showing similarities in the relative sizes of apical and body coccoliths and the presence of protruding teeth along the inner margin of apical coccoliths.

Bloom of coccolithophore Syracosphaera halldalii in the Middle Adriatic estuary

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