The results of investigations of spatial and temporal variability of C/chl a ratio in phytoplankton of the surface layer (0–1 m) in the shallow waters of the Black Sea are presented. The work was carried out in the north-western part of the sea and near Crimean coast in different months during 2005–2013 in expeditions on research vessels "Professor Vodyanitsky" and "Vladimir Parshin". Bacillariophyta, Dinophyta and Haptophyta produce the main biomass of phytoplankton in the Black Sea. The variability of abiotic environmental conditions leads to a variability of the structural and functional parameters of phytoplankton. Early studies on cultures of microalgae has been shown that the ratio between organic carbon and chlorophyll a (C/chl. a) in the algal cells depends on environmental conditions, taxonomy and cell size of algae. It is logical to assume that in the Black Sea ratio between organic carbon and chl. a will change on the background of spatial and temporal variability of environmental conditions, as well as the heterogeneity of the cell size and taxonomic structure of phytoplankton. To confirm this hypothesis, we conducted a study on the variability of the C/chl. a ratio, species and size structure of phytoplankton and associated parameters of the environment in the sea surface in different months of the warm season. Organic carbon content was calculated from the mean cell volume for each type of algae on equations (Strathmann, 1967; Menden-Deuer, 2000). Chlorophyll a concentration was measured using fluorimetric technique (Protocol JIGOFS, 1994). Studies have shown that the degree of spatial and temporal variability of the C/chl. a ratio was not the same in the different periods of the year. The minimum values of this parameter (30–72) have been observed usually in the coastal zone dominated by smaller species of Bacillariophyta and Haptophyta. The maximum values (240–330) marked in the areas farthest from the coast, dominated by Dinophyta and larger species of Bacillariophyta. Quantitative estimates show that 65 to 78 % of the variability of this parameter due to differences in light conditions in the upper quasi-homogeneous layer, as well as the heterogeneity of taxonomic and size structure of phytoplankton. The results suggest the need to consider the variability of the C/chl. a ratio for the assessment of phytoplankton biomass on concentration of chlorophyll a.

Keywords: carbon to chlorophyll a ratio, phytoplankton, the Black Sea

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