Relationship between seasonal variations of primary production, abiotic factors and phytoplankton composition in the coastal zone of the south-eastern part of the Baltic Sea

Seasonal variations in marine primary production (PP) in the coastal zone of the south-eastern part of the Baltic Sea were studied between April 2008 and April 2009. The spring PP maximum was observed to be limited by the concentration of nitrates. Following a decrease in photosynthetic consumption of nutrients, an increase in ammoniacal nitrogen due to the decomposition of organic matter and concomitant increase in the biomass of diazotrophic cyanobacterial species, the growth of phytoplankton was limited by phosphates. By the middle of summer, concentrations of nitrate and phosphates had reached the analytical minimum (0.07 mmol m(-3) and 0.06 mmol m(-3), respectively). Terrestrial runoff, whose maximum occurred during the spring-summer decline of phytoplankton growth, had a moderately positive influence on PP, with the annual rate reaching the eutrophic level (290 g C m(-2) yr(-1)); however, the seasonal cycle was typical for mesotrophic waters of temperate latitudes of the Northern Hemisphere. The most significant producers of phytoplankton biomass (PB) were representatives of the Dinophyta, Chlorophyta and Cyanophyta systematic divisions at the study site. 77% of carbon-to-chlorophyll a ratio variability was determined by the seasonal variations in green algae biomass. During the spring bloom, dinoflagellates provided the highest contribution in the total biomass in comparison with diatoms. (c) 2019 Elsevier B.V. All rights reserved.