By moving away from coastal waters and hence reducing pressure on nearshore ecosystems, offshore aquaculture can be seen as a possible step towards the large-scale expansion of marine food production. Integrated multi-trophic aquaculture (IMTA) in nearshore water bodies has received increasing attention and could therefore play a role in the transfer of aquaculture operations to offshore areas. IMTA holds scope for multi-use of offshore areas and can bring environmental benefits from making use of waste products and transforming these into valuable co-products. Furthermore, they may act as alternative marine production systems and provide scope for alternative income options for coastal communities, e.g., by acting as nodes for farm operation and maintenance requirements. This paper summarizes the current state of knowledge on the implications of the exposed nature of offshore and open ocean sites on the biological, technological and socio-economic performance of IMTA. Of particular interest is improving knowledge about resource flows between integrated species in hydrodynamic challenging conditions that characterize offshore waters.

Shifting environmental conditions resulting from anthropogenic climate change have recently garnered much attention in the aquaculture industry; however, ocean acidification has received relatively little attention. Here, we provide an overview of ocean acidification in the context of North American aquaculture with respect to potential impacts and mitigation strategies. North American shellfish farms should make ocean acidification an immediate priority, as shellfish and other calcifying organisms are of highest concern in an increasingly acidifying ocean and negative effects have already been felt on the Pacific coast. While implications for various finfish have been documented, our current understanding of how acidification will impact North American finfish aquaculture is limited and requires more research. Although likely to benefit from increases in seawater CO 2 , some seaweeds may also be at risk under more acidic conditions, particularly calcifying species, as well as non-calcifying ones residing in areas where CO 2 is not the primary driver of acidification. Strategies to mitigate and adapt to the effects of acidification exist on the regional scale and can aid in identifying areas of concern, detecting changes in seawater carbonate chemistry early enough to avoid catastrophic outcomes, and adapting to long-term shifts in oceanic pH. Ultimately, ocean acidification has already imposed negative impacts on the aquaculture industry, but can be addressed with sufficient monitoring and the establishment of regional mitigation plans.

The heavy reliance of most global aquaculture on the ambient environment suggests inherent vulnerability to climate change effects. This review explores the potential effects of climate change stressors on aquaculture biology and resources needed to support decision-making for vulnerability assessment, planned adaptation, and strategic research development. Climate change-mediated physiochemical outcomes important to aquaculture include extreme weather, precipitation and surge-based flooding, water stress, ocean acidification, sea-level rise, saltwater intrusion, and changes to temperature, salinity, and dissolved oxygen. Culture practices, environment, and region affect stressor exposure, and biological response between species or populations are not universal. Response to a climate change stressor will be a function of where changes occur relative to optimal ranges and tolerance limits of an organism's life stage and physiological processes; the average magnitude of the stressor over the production cycle; stressor rate of change; variation, frequency, duration, and magnitude of extremes; epigenetic expression, genetic strain, and variation within and between populations; health and nutrition; and simultaneous stressor occurrence. The effects of simultaneous stressors will frequently interact, but may not be fully additive or synergistic. Disease is a major aquaculture limiter, and climate change is expected to further affect plant and animal health through the host and/or infectious agents. Climate change may introduce further complexity to the aquaculture−wild fishery relationship, with over two-thirds of animal aquaculture production dependent on external feed inputs. Higher production costs could be an economic outcome of climate change for many aquaculture sectors. Some aquaculture practices may inadvertently reduce resiliency to climate change, such as a reduction of coastal vegetation, coastal ground-water pumping, and reduction of population variability in pursuit of consistent production traits. Information from the largest aquaculture producers such as China and the top 3 global culture species is still sparse in the literature. This potentially limits thorough understanding of climate change effects on some regional aquaculture sectors.

Qualifying and quantifying nutrient flows within open‐water Integrated Multi‐Trophic Aquaculture (IMTA) systems is necessary to determine transfer efficiencies and to assess overall system performance. There are numerous empirical performance metrics, such as spatially defined growth and nutrient sequestration, which may have application. When used in combination with modelling techniques, empirical approaches can be a powerful tool for system assessment or prediction. Simple empirical growth models, such as the thermal‐growth coefficient (TGC) and scope for growth (SFG), are applicable to aquatic animals and can include nutritional mass‐balance approaches to estimate nutrient loads. Comparable empirical growth models exist for seaweeds. Mechanistic‐based dynamic growth and reproduction models, such as Dynamic Energy Budget (DEB), are more complex, but have application beyond site‐specific empirical models and can, therefore, be included into larger ecosystem models for application to IMTA. Proximity, ecological transfer efficiencies, particle dynamics, species culture ratios and the timing of multi‐species production cycles can have profound implications for IMTA effectiveness and require careful consideration for system assessment. This review provides a pragmatic evaluation of performance measures and models to assess nutrient transfer and growth in open‐water IMTA systems.

Increases in global population and seafood demand are occurring simultaneously with fisheries decline in an era of rapid climate change. Aquaculture is well positioned to help meet the world's future seafood needs, but heavy reliance of most global aquaculture on the ambient environment and ecosystem services suggests inherent vulnerability to climate change effects. There are, however, opportunities for adaptation. Engineering and management solutions can reduce exposure to stressors or mitigate stressors through environmental control. Epigenetic adaptation may have the potential to improve stressor tolerance through parental or early life stage exposure. Stressor-resistant traits can be genetically selected for, and maintaining adequate population variability can improve resilience and overall fitness. Information at appropriate time scales is crucial for adaptive response, such as real-time data on stressor levels and/or species' responses, early warning of deleterious events, or prediction of longer-term change. Diet quality and quantity have the potential to meet increasing energetic and nutritional demands associated with mitigating the effects of abiotic and biotic climate change stressors. Research advancements in understanding how climate change affects aquaculture will benefit most from a combination of empirical studies, modelling approaches, and observations at the farm level. Research to support aquaculture adaptation requires an increasing amount of environmental data to guide biological response studies for regional applications. Increased experimental complexity, resources, and duration will be necessary to better understand the effects of multiple stressors. Ultimately, in order for aquaculture sectors to move beyond short-term coping responses, governance initiatives incorporating the changing needs of stakeholders, users, and culture ecosystems as a whole are required to facilitate planned climate change adaptation and mitigation.