To predict the response of the European flat oyster (Ostrea edulis) and Pacific cupped oyster (Crassostrea gigas/Magallana gigas) populations to environmental changes, it is key to understand their life history traits. The Dynamic Energy Budget (DEB) theory is a mechanistic framework that enables the quantification of the bioenergetics of development, growth and reproduction from fertilization to death across different life stages. This study estimates the DEB parameters for the European flat oyster, based on a comprehensive dataset, while DEB parameters for the Pacific cupped oyster were extracted from the literature. The DEB parameters for both species were validated using growth rates from laboratory experiments at several constant temperatures and food levels as well as with collected aquaculture data from the Limfjorden, Denmark, and the German Bight. DEB parameters and the Arrhenius temperature parameters were compared to get insight in the life history traits of both species. It is expected that increasing water temperatures due to climate change will be beneficial for both species. Lower assimilation rates and high energy allocation to soma explain O. edulis’ slow growth and low reproductive output. Crassostrea gigas’ high assimilation rate, low investment in soma and extremely low reserve mobility explains the species’ fast growth, high tolerance to starvation and high reproductive output. Hence, the reproductive strategies of both species are considerably different. Flat oysters are especially susceptible to unfavourable environmental conditions during the brooding period, while Pacific oysters’ large investment in reproduction make it well adapted to highly diverse environments. Based on the life history traits, aquaculture and restoration of O. edulis should be executed in environments with suitable and stable conditions.

1. The European native oyster (Ostrea edulis) is a threatened keystone species which historically created extensive, physically complex, biogenic habitats throughout European seas.2. Overfishing and direct habitat destruction, subsequently compounded by pollution, invasive species, disease, predation and climate change have resulted in the functional extinction of native oyster habitat across much of its former range.3. Although oyster reef habitat remains imperilled, active restoration efforts are rapidly gaining momentum. Identifying appropriate sites for habitat restoration is an essential first step in long-term project success.4. In this study, a three-round Delphi process was conducted to determine the most important factors to consider in site selection for European native oyster habitat restoration projects.5. Consensus was reached on a total of 65 factors as being important to consider in site selection for European native oyster habitat restoration projects. In addition to the abiotic factors typically included in habitat suitability models, socio-economic and logistical factors were found to be important. Determining the temporal and spatial variability of threats to native oyster habitat restoration and understanding the biotic factors present at a proposed restoration site also influence the potential for project scale-up and longevity.

Aquaculture is seen as a possible solution to meet the rising demand for fish but only if the sector reduces its use of wild fish in feed as well as its environmental impacts. The cultivation of extractive species along with fish farming (the integrated multi‐trophic aquaculture system) has a potential to mitigate the adverse environmental effects of fish farming. The dynamic energy budget (DEB) modelling is a powerful tool to be used in different aquaculture settings to achieve the Blue Growth goals set by the commission. This study explored the potential of mussel for bioremediation at finfish farms to develop environmentally sustainable finfish farming solutions in the eutrophic Baltic Sea region. The study integrated the DEB models of blue mussels Mytilus edulis/trossulus and rainbow trout Oncorhynchus mykiss and a regional hydrodynamic‐biogeochemical model to explore the potential of mussel farming to fully compensate nutrient discharges from finfish farms. The DEB models demonstrated that despite suboptimal mussel growth conditions (low salinity), mussel farming has a potential to fully compensate for the discharge of nutrients from fish farms and thereby provide a solution for sustainable fish farming in the Baltic Sea region. Synthesis and applications. As such fish farming may become a necessary enabler of economically sustainable mussel farming in the region. Mussel farming facilitates finfish farming licensing whereas finfish farming covers some costs of mussel farming thereby increasing the economic feasibility of this activity in the region.

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.

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