Soutenance de thèse de Benjamin Misteli (ECOBIO, Université de Rennes 1, OSUR)
Reviewers: Jean-Nicolas BEISEL, Professor, Ecole Nationale du Génie de l’Eau et de l’Environnement de Strasbourg Iris STIERS, Professor, Vrije Universiteit Brussel Examiner: Karl Matthias WANTZEN, Professor, Université du Tour Supervisor: Gabrielle THIÉBAUT, Professeure, Université de Rennes 1 Christophe PISCART, Directeur de recherche, CNRS Alexandrine PANNARD, Maître de conférences, Université de Rennes 1 Keywords: macrophyte removal, plant type, biodiversity, macroinvertebrates, zooplankton, phytoplankton Abstract: Rapid mass development of native and invasive macrophytes is causing global concerns. Dense mats of macrophytes can negatively affect activities like boating, fishing, etc., and one of the measures often applied is mechanical removal. Nonetheless, they provide habitats and thereby potentially support biodiversity. The effects of dense mats of macrophytes and their removal on biodiversity remain unclear. We hypothesize that dense mats of macrophytes have a positive impact on the richness and abundance of zooplankton, phytoplankton, and macroinvertebrates. Thus, the removal of macrophytes is expected to reduce biodiversity in comparison to sites where macrophytes remain. We find that dense mats of macrophytes are overall beneficial for the three studied groups, but results are site-dependent. Different community structures inside and outside of macrophytes affect the sampling efficiency. A greater sampling effort is needed within macrophytes to reach comparable sampling coverage as in the open water. We also show that different plant types affect zooplankton to a different extent though in a similar way. The mechanical removal of macrophytes negatively affects the overall biodiversity, especially of zooplankton and macroinvertebrate assemblages. In contrast, plant removal has positive effects on the phytoplankton assemblages. Effects are most pronounced one week after removal and decline over time, and they differ among sites. This thesis highlights the importance of considering impacts on ecosystem services like the provision of habitats for biodiversity in sustainable management practices of macrophytes in the future. [https://univ-rennes1-fr.zoom.us/j/85920127958](https://univ-rennes1-fr.zoom.us/j/85920127958) Meeting ID: 859 2012 7958 Passcode: 915431
