This paper studies seasonal variability of phytoplankton photosynthetic parameters in the Black Sea coastal waters near the Crimean Peninsula. Primary production was estimated using a full spectral approach that took into account phytoplankton spectral light absorption coefficient, spectral downwelling irradiance and quantum yield of photosynthesis. In the coastal waters near the village of Katsiveli, the annual dynamics of chlorophyll a concentration was characterized by maximal values in winter and minimal(half as many) in summer, while in the waters near Sevastopol, the maximum was recorded in early October and March, which is likely due to the “bloom” of phytoplankton. High annual variability of both the phytoplankton spectrally weighted chlorophyll a specific absorption coefficient(~ 3 times) and maximum quantum yield of photosynthesis(~ 7 times) was noted, with maximal values in summer and winter, respectively. In the vertical profile, the minimal values of the quantum yield were observed in the sea surface layer associated with the high photosynthetically active radiation incident on the sea surface. The variability in photosynthetic parameters, caused by phytoplankton adaptation to changing environmental factors, resulted in a strong annual variability of primary production, which varied ~8-fold over the study period. The obtained patterns of variability of the basic photosynthetic parameters of phytoplankton(the ability to absorb light quanta and use them in photochemical reactions) are necessary for understanding the mechanism of formation of primary production in the studied water region.
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