Long-Term Changes in the Primary Production of Phytoplankton in the Ecosystem of the Vistula Lagoon of the Baltic Sea

The long-term (2001-2020) data of the primary production and abundance of phytoplankton (according to the concentration of chlorophyll a) in the Vistula Lagoon under significant ecosystem changes have been analyzed. The long-term dynamics is characterized by an increase in primary production to a hypertrophic level (>450 g C/(m(2) year) in 2006-2010. After the intensive development of the bivalve filter-feeding mollusk Rangia cuneata, the primary production in 2011-2020 remained at the hypertrophic level, despite significant changes in the structure and abundance of phytoplankton. Average annual primary production in 2001-2020 was 60% higher than in 1974-1976. Primary production exceeds the mineralization of organic matter in water by 60%, which leads to the secondary eutrophication of the Vistula Lagoon and pollution of the Baltic Sea.