Samenvatting

Seagrass meadows hold significant value for local coastal communities and many different organisms by providing essential ecosystem services. However, due to anthropogenic stressors (e.g. coastal development, eutrophication etc.) seagrass meadows have been declining rapidly worldwide. In Lake Grevelingen (The Netherlands), these pressures led to asevere loss of Zostera marina meadows and the disappearance of important key species, like the grazer Littorina littorea, which are crucial for regulating epiphyte growth on seagrass.Eutrophication and the loss of this grazer further reduced Zostera marina health and resilience in Lake Grevelingen. Although several restoration attempts have been implemented in the area, success remained limited. Recently, the non-native grazer Haloa japonica has become invasive in Lake Grevelingen and could potentially fulfil Littorina littorea’s functional ecological role. This study investigated the impact of the native grazer Littorina littorea and the non-native grazer Haloa japonica on Zostera marina (by regulating epiphyte growth) under both ambient and nutrient-enriched conditions, to get a better understanding of their potential role in supporting seagrass restoration in Lake Grevelingen.