Climate change effects on phytoplankton depend on cell size and food web structure
We investigated the effects of warming on a natural phytoplankton community from the Baltic Sea, based on six mesocosm experiments conducted 2005–2009. We focused on differences in the dynamics of three phytoplankton size groups which are grazed to a variable extent by different zooplankton groups. While small-sized algae were mostly grazer-controlled, light and nutrient availability largely determined the growth of medium- and large-sized algae. Thus, the latter groups dominated at increased light levels. Warming increased mesozooplankton grazing on medium-sized algae, reducing their biomass. The biomass of small-sized algae was not affected by temperature, probably due to an interplay between indirect effects spreading through the food web. Thus, under the higher temperature and lower light levels anticipated for the next decades in the southern Baltic Sea, a higher share of smaller phytoplankton is expected. We conclude that considering the size structure of the phytoplankton community strongly improves the reliability of projections of climate change effects.
KeywordsPhytoplankton Phytoplankton Community Nutrient Depletion Heterotrophic Dinoflagellate Copepod Biomass
This work was funded by the Deutsche Forschungsgemeinschaft (DFG) within the priority program 1162 ‘The impact of climate variability on aquatic ecosystems’ (AQUASHIFT). Francisco de Castro is acknowledged for advice on computational issues. T. Klauschies also thanks Aleksandra Lewandowska for help in technical questions.
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