Seasonal changes in phytoplankton composition and nutrient limitation in a shallow Baltic lagoon

In this study we follow seasonal changes in the phytoplankton community composition in a shallow, mostly freshwater lagoon of the Baltic Sea.Nutrient enrichment effects on the quantitative and structural development of phytoplankton communities were also evaluated during short-term experiments in small-size enclosures.Different periods featuring alternate regulatory patterns of phytoplankton seasonal succession in the Curonian lagoon were derived.The spring phase is characterized by silica and phosphorus-limited conditions where nitrogen is a secondary limiting nutrient.Soluble inorganic phosphorus limits green algae, while silica limits diatoms, exclusively pennate species.In the enrichment experiments growth of centric diatom species was favoured by nitrogen addition, while pennates reaction was negative.Cyanobacteria dominated summer community is characterized by the nitrogen limitation, while phosphorus occurs as the secondary limiting factor.In general, inorganic nutrient concentrations in the hypereutrophic Curonian lagoon are too high to limit total plankton biomass, which is controlled mostly by the ambient physical factors.However, seasonal variation in nutrient concentrations could shape the phytoplankton community and, in combination with physical factors, force the seasonal succession.