According to the EU Marine Strategy Framework Directive (2008/56/EC), marine protected areas (MPA) should contribute to a good environmental status of the Europeans seas. Measures maintaining or restoring a favourable conservation status of protected species and habitats are mandatory according to the EU Habitats Directive (92/43/EEC). Identification of suitable sites for ecological restoration measures within MPAs is a crucial step towards successful conservation and sustainable MPA management. In terms of species restoration, it is important to restore the respective species with the best possible environment for growth, survival, fitness, and successful recruitment. This study provides a comprehensive list of site‐selection criteria for ecological species restoration. Three general categories were chosen: (1) ecological history: evidence for the historical distribution; (2) feasibility of restoration: regulating framework and logistics; and (3) environmental conditions: quality of abiotic and biotic factors. A total of 16 site‐selection criteria were identified and applied to biogenic reef restoration, namely for reefs of the native European oyster Ostrea edulis, in the German Bight. The Natura 2000 area Borkum Reef Ground was identified as a suitable site for oyster restoration. It is one of three MPAs in the German Exclusive Economic Zone of the North Sea, which have been declared as Nature Conservation Areas according to national legislation. The conservation objectives include maintenance or, if necessary, restoration of the habitat type ‘reefs’. As a reef‐building species, the European oyster O. edulis is of particular importance for this habitat type in terms of nature conservation. The step by step approach for site selection presented here is applicable for biogenic reef restoration elsewhere. The selected Natura 2000 area showcases the potential role and future perspective of European MPAs with regards to active conservation measures.

Oyster reefs are among the most threatened marine habitats globally. In Europe, oyster reefs have been extirpated from most locations within their historical range. Active restoration of the native oyster (Ostrea edulis) in Europe has grown substantially in recent years. In sharing experiences between oyster restoration projects in Europe at the Native Oyster Restoration Alliance conference, NORA2, in Edinburgh in May 2019, it became apparent that a number of similar barriers are experienced. This study identified the top 40 questions, which, if answered, would have the greatest influence on the policy and practice of oyster restoration in Europe. Initially 71 people were consulted across 28 institutions and 11 European countries to generate 194 questions. An established process of one round of pre‐workshop voting followed by a one‐day online workshop and two post‐workshop rounds of voting resulted in the final 40 questions. Questions were broadly grouped into the following 10 themes: baselines, site selection, restoration methods, quantifying benefits, disease management, biosecurity, genetic diversity and population differentiation, policy and management, novel technologies, and current and future threats. We anticipate that this list will provide a starting point for developing collaborative projects across the NORA network, as well as assisting policy makers and funders with identifying key areas that need to be addressed in order to overcome existing barriers to scaling up oyster restoration in Europe.

The conservation and active restoration of European flat oyster (Ostrea edulis) populations are a major focus of ecological restoration efforts to take advantage of the wide-ranging ecosystem functions and services this species provides. Accordingly, additional and new demands for seed oysters have arisen. In commercial aquaculture (mariculture), the production of O. edulis is still largely based on natural seed collection. Considering the specific requirements, related to ecological restoration, such as the absence of pathogens and the preservation of high genetic diversity, the current supply is insufficient. Despite the development of breeding and controlled reproduction techniques for this species since the late 1930s, seed production today is mainly based on empirical concepts. Several of the issues that producers still face are already subjects of research; many others are still unanswered or even unaddressed. This review provides a summary of all available knowledge and technologies of O. edulis seed production. Furthermore, it provides a detailed reflection on implications for restoration, future challenges, open questions and it identifies relevant research topics for sustainable seed supply. The study covers the following aspects on (i) biology of the species, (ii) stressorsincluding pathogens and pollutants, (iii) genetics, (iv) history of production technologies, (v) seed production in polls, (vi) seed production in ponds and (vii) seed production in hatcheries. Future research needs on sex determinism, gametogenesis, cryopreservation, nutrition, selective breeding, pathogens and disease, and the development of reliable protocols for production are highlighted.

The Native Oyster Restoration Alliance (NORA) supports the protection and ecological restoration of the native European oyster, Ostrea edulis, and its habitat across its current and historical biogeographical range. NORA works to overcome barriers to the conservation, restoration, and recovery of the European oyster by providing a platform for the NORA community to collaborate and participate in knowledge exchange. NORA seeks to support responsible restoration practice, in compliance with biosecurity and sustainability. Against this background, the NORA community formulated a series of specific recommendations, the Berlin Oyster Recommendation, to support native oyster restoration by developing and applying best practice with the aim to recover healthy and resilient marine ecosystems. In combination with the Standards for Ecological Restoration (SER) and the Restoration Guidelines for Shellfish Reefs, the Berlin Oyster Recommendation is a relevant tool for successful and sustainable oyster restoration in Europe. The establishment of NORA working groups will support the implementation and further development of the six corresponding recommendations. Current NORA working groups cover site selection, biosecurity, production, and monitoring. The site selection working group will address the identification of suitable sites for oyster restoration to support policy relevant decision making and the conservation, reinforcement, or reintroduction of native oysters. The biosecurity working group will develop biosecurity guidelines for native oyster restoration in Europe. The production working group will assess the potential of standards for seed oyster production and supply in order to enhance production appropriate for restoration purposes. In close collaboration with the Native Oyster Network – UK & Ireland (NON), the monitoring working group will produce a monitoring guidelines handbook to provide metrics and methods that will be suitable across the range of O. edulis projects in Europe for the documentation of restoration success and ecosystem recovery. The Berlin Oyster Recommendation was examined and interpreted by NORA experts in the context of the further development of joint guidelines for the practice of successful and sustainable native oyster restoration.