Spring seasonal pattern of primary production in the Gulf of Riga (Baltic Sea) after a mild winter

ABSTRACT: Spring phytoplankton production was estimated by a light and dark bottle oxygen technique in the southern part of the Gulf of Riga during spring 2014. The main study objective was to determine factors that define the spring primary productivity by analyzing the pattern of primary production and changes in succession of phytoplankton species along with environmental factors. Spring phytoplankton production was estimated by a light and dark bottle oxygen technique in the southern part of the Gulf of Riga during spring 2014. The main study objective was to determine factors that define the spring primary productivity by analyzing the pattern of primary production and changes in succession of phytoplankton species along with environmental factors. The productivity was measured after an untypically mild winter without ice-cover on the Gulf of Riga and spring flooding, which resulted in large amounts of terrestrial nutrients retained in the catchment area. At that time precipitation played a major role in riveroriginated nutrient inflow in the study area. A vague diatom bloom was stretched throughout April, followed by increase in biomass of dinoflagellate Peridiniella catenata and autotrophic ciliate Mesodinium rubrum. The total amount of spring primary production (MarchMay) reached 116.3 to 127.2 g C m–2 in the southern region of the Gulf of Riga. Our results suggest that diatoms contributed most to the “new” production and net primary production, whereas dinoflagellate P. catenata and autotrophic ciliate M. rubrum vernal production was mostly based on regenerated nutrients, although showing also the highest respiration rates.