Winter bloom of coccolithophore Emiliania huxleyi and environmental conditions in the Dardanelles

Following a summer bloom of coccolithophore Emiliania huxleyi (Lohmann) Hay & Mohler, 1967, in 2003, a winter bloom was observed for the first time between late December 2003 and early January 2004 in the Dardanelles. Microscopic observations showed that the cell dimensions of E. huxleyi (Ehux) varied from 9.85 to 13.50 μm in diameter (mean: 11.20±1.38 μm). While Ehux revealed a relatively small population density (1.60 × 10⁴ cells L⁻¹) in early December 2003, the bloom started in middle December 2003 (7.86 × 10⁶ cells L⁻¹) and then peaked in early January 2004 (5.03 × 10⁷ cells L⁻¹) in the superficial layer. The peak dramatically decreased in late January 2004 (7.50 × 10⁶ cells L⁻¹). Ehux was the dominant species and represented about 90.0% of the phytoplankton assemblage. The bloom started flourishing after the diatom and dinoflagellate blooms under nitrogen depletion and moderate light, temperature and salinity conditions. Water temperature (10.31±1.14°C) and salinity values (27.05±0.88 ppt) were usually stabile. Surface chlorophyll-a concentrations ranged from 1.23 to 2.32 μg L⁻¹ during the bloom. The ratios of N:P (mean: 4.12±2.22) and Si:P (40.35±16.25) of the bloom period were lower than those of the non-bloom periods.