Temperature-related timing of the spring bloom and match between phytoplankton and zooplankton

ABSTRACT

Global warming is causing changes in the food web structure and seasonal plankton dynamics. The Baltic Sea is one of the fastest-warming sea areas and warming consequently affects the timing and magnitude of phytoplankton blooms. Based on available Chlorophyll a data from nine years between 1979 and 2018, from the entrance to the Gulf of Finland, we studied the timing of the phytoplankton spring bloom in relation to spring seawater temperature. We found the peak of the bloom to occur earlier in years with higher spring seawater temperature. In warmer years, there was also a shorter time lag between phytoplankton and zooplankton biomass peaks. In addition, it seems as the spring bloom total biomass has decreased with time, with more extensive summer blooms during later years, in line with the general trend observed in the Baltic Sea. The spring bloom has traditionally been considered the most important part of the season, but we argue that the whole growth season should be investigated since summer blooms appear to increase with warming.

KEYWORDS:

• Baltic Sea
• climate change
• spring bloom
• timing
• vernal
• zooplankton

Acknowledgements

Funding was received from the Walter and Andrée de Nottbeck Foundation (A. K. A., T. T.) and the Swedish Cultural Foundation in Finland (T. T.). The authors appreciate the work of the authors of the articles from where historical data were obtained, and the Finnish Meteorological Institute and Tvärminne Zoological station for providing data on temperature. The authors kindly acknowledge Mirian Arellano for determining zooplankton biomass in 2016. Two anonymous reviewers are kindly acknowledged for comments that improved the quality of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Funding was received from the Walter and Andrée de Nottbeck Foundation (Walter ja Andrée de Nottbeckin Säätiö) (A. K. A., T. T.) and the Swedish Cultural Foundation in Finland (Svenska Kulturfonden) (T. T.).