A trait-based perspective on consequences of biodiversity loss in freshwater plankton communities

Changes in communities of planktonic organisms occur at small spatial and temporal scales, but can have consequences for entire aquatic ecosystems, their biodiversity, trophic interactions and biogeochemical cycles. The global biodiversity crisis affects in particular freshwater ecosystems. It is hence crucial to understand the consequences of a loss in functional diversity on phytoplankton-zooplankton interactions. In this context, trait-based approaches are particularly useful to investigate how the loss of specific functional traits (rather than taxa) impacts ecosystem functioning. We here used a combination of controlled laboratory and field mesocosm experiments to investigate the consequences of losses in phytoplankton trait diversity on the pelagic plant-herbivore interface. We demonstrate that phytoplankton trait distributions are affected by both physical (hydrodynamic disturbance) and biological (size-selective zooplankton grazing) factors. In turn, these alterations in phytoplankton trait distributions feed back on the algal nutritional quality for herbivorous zooplankton. This trait-based approach therefore allowed us to highlight the intricate regulation mechanisms between fitness-relevant phytoplankton and zooplankton traits of lakes in a changing world.