The A.O. Kovalevsky Institute of Marine Biological Research of RAS, RF, Sevastopol, Nachimov av., 2
Based on the field studies conducted in the Black Sea from 2005 to 2013, the assessment of the impact of phytoplankton adaptation to environmental conditions on the distribution of its biomass and chlorophyll a concentration in the surface layer of water (0–1 m) in the warm season was made. As an indicator reflecting adaptation processes in the phytoplankton community, we used the ratio between organic carbon and chlorophyll a (C/Chl a). This structural parameter of phytoplankton responds quickly to changes in abiotic environmental factors and above all such factors as light and nutrients.
It has been established that in various regions of the Black Sea during the warm period of the year the C/Chl a ratio was, as a rule, unequal. Its values reached differences by a factor of 2,5–10. They are maximal under the conditions of the greatest variability over the water area of the average intensity of light in the upper mixed layer (IUML) and the concentration of mineral forms of nitrogen in water, as well as the average cell volume of the phytoplankton community and its taxonomic structure. With a decrease in the variability of abiotic parameters and an increase in taxonomic differences in the phytoplankton of the studied waters, due to the unequal contribution of dinophyta algae to its total biomass, the C/Chl a ratio variability reached 5 times. It determined different distribution patterns of phytoplankton biomass and chlorophyll a concentration over the water area.
With insignificant changes in the values of IUML and the concentration of mineral forms of nitrogen and practically the same size structure of phytoplankton, in which small algal cells prevailed, the C/Chl a ratio differed no more than 2,5 times. Therefore, the nature of the distribution of phytoplankton biomass and chlorophyll a concentrations was almost the same.
Our results suggest that phytoplankton biomass estimation by chlorophyll a concentration should be carried out taking into account the C/Chl a ratio.
Keywords: phytoplankton biomass, chlorophyll a, nutrients, solar radiation intensity, the Black Sea.
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