Conclusions
As extreme events caused by climate change are increasing in frequency and duration, it is important to develop a mechanistic understanding of how ecosystems respond to temperature changes. Here we use a trait- and size-structured model to study the effect of seasonal heatwaves on plankton organisms. In the model, the plankton functional diversity is represented by the traits of cell/body size, energy uptake (auto-, mixo- and heterotrophy) for protists, and the life cycle of copepods with two feeding modes (active, passive). The model showed that heatwave effects on biomass, diversity, and community composition are present not only during the heatwave but for up to six years after the temperature perturbation. Autumn and summer heatwaves have the most profound anomalies and longest-lasting effects, followed by winter and spring heatwaves. Our results indicate that temperature can alter the dominance of size groups, but temperature alone cannot lead to fundamental changes in the community size structure and more environmental factors need to be taken into consideration. In our study, we found a variety of population and community alterations during the heatwave and different recovery times to the pre-heatwave state. Two factors drive those results: the heatwave temperature anomaly compared to the mean seasonal temperature fluctuation and plankton functional diversity. Communities have longer recovery times when experiencing seasonal heatwaves with temperature anomalies outside the pre-heatwave seasonal temperature fluctuation. Including functional diversity is crucial for exploring ecosystem changes as protists, active, and passive copepod feeders have dissimilar responses to the heatwaves, as well as recovery periods. Our model provides a mechanistic framework with ecological realism, flexible enough to scale up and down in complexity and test hypotheses for future studies.