Algal blooms in surface waters of the Sinop bay in the Black Sea, Turkey

During the investigation period of August-1995 and July-1996, 22 algal species reached numerical densities exceeding 1.0x105 cells L-1 and it has been produced 17 mono-specific blooms by 11 of them reached values of the order of 1.0 x 106 cells L-1 (one of them exceeding 1.0 x 107 cells L-1) in surface waters of the Sinop Bay. A monthly average of cell number has been estimated as 7.1 x 106 cells L-1 in the surface waters. In the diatom communities, subsequent blooms were dominated by Nitzschia longissima (5.2 x 106 cells L-1) and Cheatoceros danicum (2.7 x 106 cells L-1) in January, Ditylum brightwelli (7.6 x 105 cells L-1) in March, Pseudo-nitzschia delicatissima (9.0 x 107 cells L-1) in April, Cylindrotheca closterium (7.4 x 106 cells L-1) in early July, Rhizosolenia calcar-avis (1.7 x 106 cells L-1) and Pseudo-nitzschia pungens (1.2 x 106 cells L- 1) in late July and mid-August. Subsequent blooms in the dinoflagellate communities were dominated by Heterocapsa triquedra (1.0 x 106 cells L-1) and Protoperidinium depressum (1.0 x 105 cells L-1 ) in March , Protoperidinium granii (4.8 x 105 cells L-1) and Scripsiella trochoidea (7.8 x 105 cells L-1) in June, Prorocentrum balticum (9.0 x 106 cells L-1) and Prorocentrum compressum (4.6 x 105 cells L-1) in mid- July, Gonyaulax polyedra (1.4 x 105 cells L-1) in June, Prorocentrum micans (7.2 x 105 cells L-1), Prorocentrum minimum, Protoceratium aerolatum, Protoperidinium longipes (2.0 x 105 cells L-1) in mid- August and Prorocentrum aporum (1.0 x 106 Cells L-1) in December. The highest cell numbers of prymnesiophyte Emiliania huxleyi (5.9 x 106 cells L-1) was observed in mid-July. Results showed that the declines of diatoms were followed by increases of dinoflagellates. Dinoflagellates began to increase in late-March, reached a maximum in Mid-July and gradually declined towards October. In contrast to the diatom, dinoflagellates dominated mid-spring, late summer and mid-winter populations, dinoflagellate blooms showed more pronounced in late spring and mid-summer. The mean of cell numbers of total phytoplankton in surface waters was high in April (3.4 x 107 cells L-1) and July (1.3 x107 cells L-1), while was low in February (9.0 x 105 cells L-1), respectively. A list of excessive and potential excessive phytoplankton species together with numerical densities were prepared. Changes in number and density of algal blooms during the year were also discussed in relation to the physico-chemical features of the water column.