Description: The dataset compiles counts of larvae of the European flat oyster Ostrea edulis, settled on various substrates under three different experimental conditions. The data was collected within the AWI-RESTORE project (Alfred-Wegener-Institute, Germany), examining basic preconditions for successful restoration of the European flat oyster within the German Bight. The data is separated in three experimental setups: the columns for experiment 1 (hatchery/laboratory) include date stamp in ISO format, Latitude, Longitude, abiotic factors (Flow rate, temperature, salinity, pH, dissolved oxygen), substrate types, area and orientation as well as the count of settled larvae for each set-up. Data for experiment 2 (hatchery) include date stamp in ISO format, Latitude, Longitude, abiotic factors (Flow rate, temperature, salinity, pH), reef number, specifics of examined area and orientation as well as the count of settled larvae for each reef. Columns for experiment 3 (field) include date stamp in ISO format, Latitude, Longitude, abiotic factors (depth, temperature, salinity), chlorophyll concentration, substrate types, specifics and orientation as well as the count of settled larvae for each submerged substrate.

Description: Growth is an important biological trait and monitoring metric for the assessment of the success and progress of restoration projects with the European oyster (Ostrea edulis). However, sampling time and frequency are often limited, as well as the ability to survey individual growth. Chemical dyes, such as calcein, can be used to create incremental markings for measuring growth in shell cross-sections, especially in bivalves. However, potential negative effects and limits for successful staining have not been assessed for O. edulis, yet. In this study, three different calcein concentrations (100-mg l-1, 150-mg l-1, 200-mg l-1) with three different immersion times (6-h, 12-h, 24-h) were tested for potential negative effects, the best incremental marking result and their potential to be used in growth measurements. Furthermore, the deposition of an annual growth line was investigated. Results showed that calcein is a reliable in situ fluorescence marker that produced sufficient growth lines in the cross-section of O. edulis. At a concentration of 100-mg l-1 or higher and immersion times of 6-h or more, no negative effects on growth and survival were observed after five months. Applications include the possibility for long-term, individual growth data for a large number of oysters for restoration monitoring as well as the option of marking restored oysters from aquaculture production to distinguish them from existing wild stock populations or natural offspring.

Description: Against the background of the UN decade on ecosystem restoration and the new EU Biodiversity Strategy for 2030, and in the context of marine spatial planning and complex maritime user conflicts, reliable information on habitat suitability for large-scale restoration is an important prerequisite for implementing conservation management and for supporting successful, sustainable, and ecologically efficient restoration measures. In this study, habitat suitability was assessed using multicriteria decision analysis (MCDA) for the restoration of the European oyster, Ostrea edulis, in marine protected areas (MPAs) of the German Bight in the North Sea: Borkum Reef Ground (Borkum Riffgrund, BRG) and Sylt Outer Reef – Eastern German Bight (Sylter Außenriff, SAR). Based on site selection criteria, exclusion and suitability factors for the MCDA were defined. Results were integrated with the available geodata to produce habitat suitability maps for oyster restoration in the area of interest. Suitable as well as unsuitable habitats have been successfully identified for both MPAs: several hundred square kilometres (≥97.2% of BRG) or several thousand square kilometres (≥74.5% of SAR) were classified as ecologically and logistically suitable for oyster restoration measures in the respective MPAs. As oyster restoration is significantly limited by human activities (e.g. bottom trawl fisheries), the management of fisheries is an important prerequisite for successful oyster restoration in both MPAs. Results show that designated fishery management measures will increase the possibilities for oyster restoration. In BRG, our results correspond to the known historical distribution. In SAR, our results significantly exceed the historically known distribution. The habitat suitability analysis will facilitate decision-making regarding ocean use, and will reduce restoration costs through targeted management activities in areas of high suitability and expand species recovery by improving the survival of reintroduced individuals. The habitat suitability analysis procedure is easily adaptable for application to other areas, other species, or other habitat restoration projects, or to other conservation management settings. The software applied is open source and the suitability calculation is described in detail to inform wider applications.

Description: The European flat oyster, Ostrea edulis, is a habitat-forming bivalve which was historically widespread throughout Europe. Following its decline due to overfishing, pollution, sedimentation, invasive species, and disease, O. edulis and its beds are now listed as a threatened and/or declining species and habitat by OSPAR. Increasing recognition of the plight of the oyster, alongside rapidly developing restoration techniques and growing interest in marine restoration, has resulted in a recent and rapid growth in habitat restoration efforts. O. edulis seed supply is currently a major bottleneck in scaling up habitat restoration efforts in Europe. O. edulis has been cultured for centuries, however, research into its culture declined following the introduction of the Pacific oyster, Crassostrea gigas to Europe in the early 1970 s. Recent efforts to renew both hatchery and pond production of O. edulis seed for habitat restoration purposes are hampered by restoration project timelines and funding typically being short, or projects not planning appropriately for the timescales required for investment, research-and-development and delivery of oyster seed by commercial producers. Furthermore, funding for restoration is intermittent, making long-term commitments between producers and restoration practitioners difficult. Long-term, strategic investment in research and production are needed to overcome these bottlenecks and meet current ambitious restoration targets across Europe.

Description: The European flat oyster, Ostrea edulis, once formed extensive reef habitats throughout European seas and estuaries. These reefs are now largely functionally extinct, yet interest and support for their restoration is rapidly growing. A major bottleneck to scaling up oyster reef restoration is the lack of available oysters to supply the growing demand. This study aimed to identify the ten questions which, if answered, would increase the consistency and success in hatchery production of O. edulis for habitat restoration. Candidate questions were submitted by representatives from twelve commercial and research hatcheries across Europe. The list of 98 candidate questions were collaboratively discussed by experts from nine research hatcheries across eight countries in Europe, to identify the top ten questions via an iterative and open process. Questions were grouped into the following themes: Conditioning and feeding, larval rearing, disease and water quality, hatchery protocol, genetics, and hatchery management. There were several overarching topics spanning these themes, including diet optimisation, maximising the effective population size, and developing the technical skillbase in order to increase hatchery production to meet the projected increase in demand for oyster seed for habitat restoration efforts. We anticipate this list will provide a starting point for collaborative research efforts across Europe, as well as assisting policy makers and funders in identifying key knowledge gaps.

Description: Ecological restoration includes specific technical phases over the course of an ecosystem recovery process. In the marine environment and for oyster reef restoration, the installation and implementation of pilot reefs close the gap between feasibility studies with small-scale experiments and designated upscaling for marine conservation measures. Against this background, this study presents the design, planning and installation of the first pilot oyster reef in offshore sublittoral regions of the North Sea. The work was conducted as part of marine protected area management in the Natura 2000 site Borkum Reef Ground in the German Bight, in the area of historical offshore oyster grounds. It includes logistical considerations, material selection, methodology for reef base construction and deployment of European flat oysters Ostrea edulis as spat-on-shell, young and adult single seed oysters, and spat-on-reef, as well as the development of an efficient monitoring approach for reef-associated biodiversity. Native Oyster Restoration Alliance monitoring methodologies, such as underwater visual census and seabed images were selected, tested and successfully adapted for the pilot oyster reef and study site. The evaluation and optimization of offshore sublittoral oyster reef monitoring are presented here, and biodiversity metrics are put into perspective with data from recent and historical studies. Results show a few mobile fauna species (e.g., fish and decapods) as first colonizers after reef construction. One year later, biodiversity increased due to a larger number of invertebrate and fish species. However, the pilot oyster reef community still represents an early recolonization stage, with lower biodiversity than historical records. This study presents a proof of concept for the design, planning and construction of an offshore oyster reef and indicates stages in the recovery process. Strategies to optimize and to complement reef-monitoring in challenging environments are discussed, emphasizing additional molecular and functional analyses for future assessments.