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Wasmund N, Nausch G, Gerth M, Busch S, Burmeister C, Hansen R, Sadkowiak B
Extension of the growing season of phytoplankton in the western Baltic Sea in response to climate change
The onset and duration of phytoplankton blooms in the western Baltic Sea are shifting. Assuming a threshold of 750 mg m–3 biomass for the phytoplankton growing season, Wasmund and colleagues detected an increase in the growing season by 125 d from 1988 to 2017. The onset of the phytoplankton spring bloom was 1.4 d yr–1 earlier across the study period, which correlated with the increase in observed sunshine hours. Similarly, the end of the autumn bloom was delayed by 3.1 d yr–1, due to increased water temperature. The summer biomass minimum was considerably lower in recent years (2014–2017) compared to earlier years (1988–1992). Shifts also occurred in the spring diatom Skeletonema marinoi bloom from May to February, as well as the Dactyliosolen fragilissimus diatom bloom, which shifted from summer to autumn. These findings may have considerable consequences for the western Baltic Sea food web.