Ecological restoration of European flat oysters in the German Bight

Several marine ecosystems currently face severe degradation, in the form of habitat loss. As a consequence, humans are undertaking initiatives to restore species and habitats to restore and preserve ecosystem services and functions. Although there have been many initiatives to restock commercial marine species for fisheries and aquaculture, the restoration of marine habitats is a relatively new discipline. To recover ecosystem conditions that maintain their structure and function, ecological restoration was conducted and implemented by the Alfred-Wegener-Institut Helmholtz Zentrum für Polar- und Meeresforschung (AWI) and the Bundesamt für Naturschutz (BfN) for re-establishing lost and ecologically relevant biogenic oyster reefs in the frame of marine conservation measures in the German North Sea. From 2016 to 2019, the AWI-led and BfN-funded RESTORE project actively investigated the technical and biological feasibility of restoration, from which this thesis originates. In this context, three key topics (and their associated subtopics), relevant for the development of a successful restoration programme, are addressed in this thesis: I) Oyster supply - How can we provide ecological restoration efforts with substantial amounts of appropriate Ostrea edulis seeds (i.e. gametes, larvae and spat)? Which production techniques and knowledge exist? Which are appropriate for restoration? II) Supply of essential settlement substrate for the oyster life cycle - Which types of substrate to use in accordance with biological traits of O. edulis? Which types of substrate to use in accordance with legislative restrictions? III) Biosecurity aspects of oyster restoration - How to avoid the transfer of pathogens or invasive species during ecological restoration projects (focusing on seed production and substrate transfer)