What are the seasonal changes in eukaryotic plankton communities and their trophic relationships in three Mediterranean coastal lagoons?

Coastal lagoons are systems threatened by anthropogenic pressures. In order to develop and apply adapted management strategies, it is essential to understand their ecological functioning. In particular, eukaryotic plankton communities play a fundamental role in sustaining the entire trophic network and functioning of the ecosystem. We used DNA-metabarcoding to study seasonal diversity and trophic interactions of plankton communities in three Corsican coastal lagoons with contrasting morphologies and functioning. The main results demonstrate the influence of seasonal and morphological factors on community structure and trophic relationships among these planktonic communities. Biguglia favors an herbivorous food web but is dominated by mixoplankton, Urbino is distinguished by a high diversity of heterotrophic protists, and Santa Giulia by the development of picophytoplankton and the emergence of a protozooplankton community. This study also shows the emergence of mixoplankton including potentially harmful dinoflagellates present in the three lagoons, and sometimes dominant, linked to anthropogenic pressure, and highlights their integration into the trophic networks in relation to the lagoon characteristics. This is a fundamental step towards understanding plankton succession and ecological network functioning in different coastal lagoon configurations, and thus towards the thoughtful management of these ecosystems under current and future pressures.