Analysis and modelling of the interactive effects of temperature and light on phytoplankton growth and relevance for the spring bloom

Global climate change alters the relationship between temperatureand light in aquatic ecosystems, which is expected to affectthe success of different phytoplankton species. To examine this,the interactions between temperature, photoperiod and lightexposure (LE) (integral daily light supply) on specific growthrates were analysed for Limnothrix redekei, Planktothrix agardhii(cyanobacteria), Nitzschia acicularis and Stephanodiscus minutulus(diatoms). A model of factor interactions was developed basedon new (P. agardhii and St. minutulus) and previously publishedlaboratory studies. It describes the measured data with highprecision. Temperature and photoperiod affect the parametersof the light-growth response curve differently, but these effectsare the same for all species. The link between functions fortemperature and photoperiod is more species-specific. Usingmeteorological data, the model developed here was used to studythe interplay of these factors during a spring bloom in LakeMüggelsee (Berlin). It was found that while all three factorsinfluenced phytoplankton growth, temperature and photoperiodwere more important than LE. Both the intensities of the factorsand the interactions between them influenced each species toa different degree. The results may help improve our understandingand ability to predict shifts in phytoplankton communities causedby weather patterns and climate change.