Farming the High Seas: Biological performance of the offshore cultivated oysters Ostrea edulis and Crassostrea gigas in the North Sea.

Aquaculture production plays an increasingly important role to meet the global demand for aquatic products and expands continuously. Most mariculture organisms are produced in coastal areas, where space is scarce and stakeholder conflicts exist. For extensive cultures farming off the coast at offshore sites could be a solution to eliminate these problems and facilitate further expansion of environmentally friendly and sustainable aquaculture. The aim of this study was to examine the biological adequacy of two candidate species for such an offshore ostreiculture, the European flat oyster Ostrea edulis and the Pacific oyster Crassostrea gigas. Research focused on growth, condition and survival. Oyster spat of both species was transferred to different offshore sites in the North Sea in 2004 and 2007 and cultivated for six month during growing season. Samples were taken every six to eight weeks from April to October and growth rates, condition indices and survival rates were measured. To enable a deeper insight in oyster condition, elemental (carbon, nitrogen) and biochemical compositions (protein, glycogen and lipid levels) as well as lipid class and fatty acid compositions were investigated. Furthermore, the macroparasitic infestation of oysters at offshore cultivation sites and for comparison, at nearshore wild banks, was investigated. Low infestation rates or even a complete absence of such parasites would be a major advantage for shellfish production activities and would therefore play an important role in the list of site-selection criteria for a certain region. Results showed that both oyster species grow successfully in high-energy offshore environments. Mean growth rates were similar to those measured in individuals from coastal habitats (wild banks and cultures) and the condition index revealed normal seasonal variations in both species. Survival rates of both species were extremely high. However, at one single site a high mortality rate was observed for O. edulis at the end of the experiment. Differences in the increase of shell length and dry mass were observed between sites and size classes. Taking these results into account site selection criteria for different offshore locations are presented. Biochemical results showed an increase in glycogen from spring to early summer for both species, which is related to high food abundance during spring phytoplankton bloom. However, during summer, glycogen storage revealed clear differences between O. edulis and C. gigas: glycogen levels decreased substantially in C. gigas, eventually owing to reproductive activity only of the Pacific oyster. Total protein did not show significant seasonal variations, while lipids were accumulated during growing season, more pronounced in C. gigas, and decreased in autumn. Phospholipids and triacylglycerols were the main lipid classes in both species. Fatty acids resembled the compositions of nearshore grown oysters. This indicates that oysters exhibited a natural biological performance during offshore cultivation. Additionally, no macroparasites have been found in oysters from offshore cultivation sites, which provides a high-potential advantage for aquaculture activities in the open ocean. It can be summarized that oysters are successful candidates for offshore aquaculture operations, e.g. as a multi-use of offshore wind farming areas. As oysters are bioextractive organisms, oyster cultivation as an essential component of integrated multi-trophic aquaculture (IMTA) approaches in offshore areas is recommended in particular

Return of the native: Survival, growth and condition of European oysters reintroduced to German offshore waters

The European oyster (Ostrea edulis) is under significant threat across its natural distribution range and even functionally extinct in some regions, such as in the German North Sea. Due to its ecological significance in terms of biodiversity and other ecosystem services, the species, and the habitat it provides, are defined as highly endangered by the OSPAR Convention. Restoration measures are gaining momentum in Europe and conclusive recommendations for large‐scale biogenic reef restoration are relevant for example within the Marine Strategy Framework Directive and the Habitats Directive. This study examined whether present‐day environmental conditions of sublittoral offshore waters are ecologically suitable for the return of European oysters. Seed oysters (shell length ~2 mm) were deployed in cages in offshore field experiments in 10–26 m water depth. Survival, growth, and condition were investigated over the course of 2 years. Survival was high, even over winter. Growth was excellent, with oysters reaching a mean length of 55.0 ± 7.2 mm shell length and 19.2 ± 6.1 g wet weight after 2 years. The formation of firmly aggregated oysters was observed and confirms O. edulis as a reef‐building species. The overall condition of oysters in the field was excellent, identified by high condition indices and early reproductive activity. These findings are highly relevant for future restoration measures in the North Sea as they confirm that present‐day environmental conditions and small, hatchery‐produced seed oysters are suitable of supporting sustainable and successful restoration efforts even in sublittoral offshore waters

Die Wiederansiedlung der Europäischen Auster

Bodenschleppnetz-Fischerei und die nicht nachhaltige Entnahme der heimischen Europäischen Auster Ostrea edulis führten dazu, dass die einst weit verbreitete Art in einigen Regionen als in- zwischen ausgestorben gilt. Als ökologische Schlüsselart hat sie jedoch viele positive Effekte für andere Pflanzen und Tierarten und leistet wichtige Ökosystemleistungen für ihre gesamte Umwelt. Nun tüfteln Wissenschaftler*innen daran, wie sich diese biogenen Strukturen, die Aus- tern nach und nach bilden, bestmöglich wieder ansiedeln lassen. Auch die kontinuierliche Nachzüchtung der dafür nötigen Larven ist geplant

Direct multiplex PCR-NALFIA to inform marine conservation: Use of an innovative diagnostic tool for the detection of Ostrea edulis larvae

The European oyster Ostrea edulis played a key role in the North Sea by providing several ecosystem functions and services. Today, O. edulis is classified as severely degraded or functionally extinct in Europe. Marine conservation is focusing on biogenic reef restoration, namely the restoration of O. edulis in Natura 2000 sites of the North Sea. The identification of oyster larvae related to natural spatfalls of restored reefs and monitoring of larval drift is a key aspect of marine protected area management. Morphological identification and distinction from other abundant bivalve larvae using microscopy is difficult. Existing molecular biological methods are expensive and bound to stationary laboratory equipment, or are inadequate in the visualization. In this study, we identified nucleic acid lateral flow immunoassay (NALFIA), a well-established tool in human pathogen diagnostics, as an efficient approach for point-of-care (POC) testing in marine monitoring. Based on the genetic sequence of the mitochondrial cytochrome b of O. edulis, forward and reverse primers were developed. The reverse primer was labelled with fluorescent dye FITC, forward primer with biotin. Reaction on the lateral flow stripe could be realized with a single O. edulis larva in direct PCR with multiplex primers in a portable PCR-cycler. The established NALFIA system can distinguish O. edulis larvae from Crassostrea gigas and Mytilus edulis larvae, respectively. This method offers new approaches in POC testing in marine research and monitoring. It gives quick and clear results, is inexpensive, and could be easily adapted to other species of interest

Site selection for biogenic reef restoration in offshore environments: The Natura 2000 area Borkum Reef Ground as a case study for native oyster restoration

1. 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). 2. 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. 3. 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. 4. 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

Potential of calcein staining as growth monitoring marker in Ostrea edulis

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

The Native Oyster Restoration Alliance (NORA) and the Berlin Oyster Recommendation: bringing back a key ecosystem engineer by developing and supporting best practice in Europe

Efforts to restore the native oyster Ostrea edulis and its associated habitats are gaining momentum across Europe. Several projects are currently running or being planned. To maximize the success of these, it is crucial to draw on existing knowledge and experience in order to design, plan and implement restoration activities in a sustainable and constructive approach. For the development of best practice recommendations and to promote multidimensional knowledge and technology exchange, the Native Oyster Restoration Alliance (NORA) was formed by partners from science, technology, nature conservation, consultancies, commercial producers and policy-makers. The NORA network will enhance scientific and practical progress in flat oyster restoration, such as in project planning and permitting, seed oyster production, disease management and monitoring. It also focuses on joint funding opportunities and the potential development of national and international regulatory frameworks. The main motivation behind NORA is to facilitate the restoration of native oyster habitat within its historic biogeographic range in the North Sea and other European seas along with the associated ecosystem services; services such as enhancing biodiversity, including enhanced fish stocks, nutrient cycling and sediment stabilization. NORA members agreed on a set of joint recommendations and strongly advise that any restoration measure should respect and apply these recommendations: The Berlin Oyster Recommendation is presented here. It will help guide the development of the field by developing and applying best practice accordingly. NORA also aims to combine the outreach activities of local projects for improved community support and awareness and to provide educational material to increase knowledge of the key ecological role of this species and increase awareness among regulators, permit providers and stakeholders. A synthesis of O. edulis restoration efforts in Europe is provided and underlines the general significance in the field

The benefits of bivalve reef restoration: a global synthesis of underrepresented species

This is the final version. Available on open access from Wiley via the DOI in this recordBivalve habitat restoration is growing in geographic extent and scale globally. While addressing the wide‐scale loss of these biogenic habitats is still a key motivation behind restoration efforts, stakeholders and funders are increasingly drawn to shellfish restoration for the many ecosystem services these habitats provide. There is clear evidence for the provision of ecosystem services from species targeted for restoration in the USA, in particular Crassostrea virginica. Ecosystem services, however, remain largely unquantified or even undescribed for the majority of other species targeted for restoration. A structured review of the literature was undertaken and supplemented by expert knowledge to identify which ecosystem services are documented in the following other bivalve species targeted for restoration: Ostrea edulis, Ostrea angasi, Crassostrea rhizophorae, Perna canaliculus, Modiolus modiolus, Mytilus edulis, Mytilus platensis, Crassostrea gigas, Ostrea denselamellosa, Crassostrea ariakensis, and Crassostrea sikamea. Key knowledge gaps in quantifying ecosystem services and the ecosystem engineering properties of habitat‐building bivalves contributing to the provision of ecosystem services were identified. Ecosystem services with the potential to be widely applicable across bivalve habitat‐building species were identified. Though there is evidence that many of the ecosystem engineering properties that underpin the provision of ecosystem services are universal, the degree to which services are provided will vary between locations and species. Species‐specific, in situ, studies are needed in order to avoid the inappropriate transfer of the ecosystem service delivery between locations, and to further build support and understanding for these emerging targets of restoration.Glenmorangie DEEP projectHWU EGISEuropean Unionerman Federal Agency for Nature ConservationEuropean Union Horizon 202

NORA moving forward: Developing an oyster restoration network in Europe to support the Berlin Oyster Recommendation

1. 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. 2. 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. 3. 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. 4. 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