Seasonal and interannual variations of the abundance of the dinoflagellate Noctiluca scintillans in the northern Black Sea

Abstract

ABSTRACT Noctiluca scintillans (Macartney) Kofoid and Swezy, 1921 contributes ∼ 85% of the total biomass of heterotrophic plankton in Crimean coastal waters. Data for the retrospective analysis come from a 20-year sampling (in 2000s) across the Crimean shelf and in adjacent open sea waters. Samples were collected onboard research vessels, in the upper 150 m layer, by Juday nets (vertical hauls) fitted with 145 µm mesh. These data were compared to field surveys of the 1960s. Seasonal blooms of Noctiluca were pronounced during summer time, with the peak of abundance in June. The mesoscale spatial distribution of Noctiluca abundance was most heterogeneous in June as well. The annual concentration of cells in coastal waters exceeded that of the open sea by four times. The coefficient of Noctiluca seasonal abundance variation in coastal waters was 1.5 times higher than that of the open sea. The Principal Component Analysis implied that the seasonal variation of the Noctiluca abundance offshore was modulated by coupling of the atmospheric precipitation, sea surface temperature, photosynthetically active radiation, euphotic depth, chlorophyll-a concentration, Noctiluca abundance in coastal waters, mesoscale eddies and wind stress. A general decline of Noctiluca abundance and biomass was observed in coastal waters, from the 1960s to the present.