The world’s ever-growing population is eating more and more fish and the production of our oceans cannot keep up. The solution has so far been to complement fishing with farmed aquatic organisms, in large following the same development seen on land, i.e. moving from “hunting and gathering” to farming. Aquaculture is today considered the only viable option for meeting the increasing future demand for fish and seafood products. However, while aquaculture has provided economic and nutritional benefits to millions, there are concerns that unconstrained sectoral expansion and intensification, coupled with its ecological and social impacts, globalisation and fluctuation of markets and resources, climate change, etc. may have undesirable impacts on the resilience of social-ecological systems. For example, a significant part of the aquaculture expansion is expected to occur in coastal areas, where it directly affects natural resource systems already experiencing large pressure from human activities. Thus, depending on species, culture system and siting, there is a risk that anticipated benefits from aquaculture may come at the expense of increased pressure on ecosystem functions and services upon which poor people in particular depend for food security and livelihoods. Even if farming activities take place in offshore environments, intensification and the choice of aquaculture species that require condensed high-quality resource inputs (especially feeds) indirectly increases the dependence on provisioning services from both terrestrial and aquatic ecosystems at a global scale. It needs to be emphasised, however, that intensification may not in itself be negative, as it can be one way for aquaculture development to meet constraints on land/sea surface availability or the need to dissociate the farm system from the local environment to avoid negative effects from e.g. parasitic infestation.

The development of aquaculture has directly contributed to the loss of important ecosystem functions through land and seascape transformation, and also more indirectly through e.g. pollution. On the other hand, aquaculture has also enhanced provisioning services, both in the agriculture landscapes and in the seascape, thus leading to improved welfare. It also constitutes a substitute to today’s terrestrial animal production, which for some sectors can be highly resource consuming. The question then is how to balance the negative and positive consequences from an environmental integrity perspective.

Looking at the diversity of farming systems, it is easy to understand that the biophysical impacts of aquaculture activities, i.e. magnitude and spatial scale, will vary enormously. Impacts could vary with species, culture system, intensity of production method and quality of management, and include issues such as: nutrient enrichment or depletion, effects of chemicals, disturbance or replacement of local ecosystems, exotic species introductions, flow of exotic genetic material from farmed to wild populations, transmission of disease/parasites, consumption of capture fishery resources, energy dependency and associated greenhouse gas emissions. To identify direct and indirect environmental effects from aquaculture activities, a wider system perspective is needed. Thus, it is not enough to discuss the local effects of aquaculture production in an analysis of the sustainability of the industry, as trade in a globalised world connects farms to distant ecosystems (and markets). A value chain approach, which captures up- and downstream activities (seed and feed production, distribution, processing, transport, etc.), follows an “ecosystem perspective” that extends far beyond the farm border (regional to global). Trade of final products and resources also increasingly interlinks different food production systems at the global scale. This does not only have implications for supporting resource systems, but volatility spillovers from e.g. the agricultural or fishery market can also have significant effects on vertically related markets such as aquaculture, resulting in increased vulnerability.

To meet future expected demands for food (i.e. protein), it is argued that aquaculture production will have to continue to expand, maybe at an even higher rate than seen today, as global capture fisheries is in decline. A relevant question to ask then is “what kind of aquaculture should be developed considering environmental and social implications and boundaries?”; but maybe we also need to more closely compare aquaculture with competing alternatives to find out which are the most sustainable options. Aquaculture represents only one of many avenues for providing food, and its strengths and limitations must be carefully considered. Such comparisons should be made not only to fisheries and livestock, but also to non-animal food products as well. The local/regional/global “space” available for aquaculture expansion should then also be weighted against other stakeholders’ (sectors’) access right across the entire socio-economic spectrum. A challenge here is to improve our understanding about ecosystems functions and the services they provide, i.e. about complexity and what structures and processes support and create resilience of these systems. This perspective implies acknowledging that uncertainties and nonlinearities exist and that these must be considered in management.

It is clear that the expansion of aquaculture will face many different challenges over the next decades, ranging from environmental, socio-economic and technological to policy-related challenges. From a general global perspective, the development of sustainable feeds will be put high on the research agenda; this is especially relevant for mariculture and brackishwater culture but will also be important for some freshwater fish species. The intricate interconnectedness with capture fisheries needs to be carefully evaluated, as well as aquaculture’s role in food security and the equitable distribution of resources. Recent positive trends in feed development for i.e. carnivorous fish species show the decreased need for inclusion of fish products and the development of alternative sources for proteins and oils. It is, however, important that the feed development does not become a “problem shifting” development, i.e. that the pressure for protein-rich compounds is only being moved from the fishery sector to the agriculture sector. It is also important to acknowledge that maintenance of environmental integrity for sustainable development of aquaculture will require not only technical advances (e.g. ecotechnology) but also changes in the institutional framework (legal and policy frameworks, regulatory capacity, implementation mechanisms).

Aquaculture makes demands on, but also can provide a range of ecosystem services that are site, species, production system and culture method dependent. The question arises how best to guide the development of aquaculture in a region whose ecosystem services are increasingly under pressure from a combination of factors in order that it plays its part in developing and maintaining food production and/or a portfolio of livelihoods. Aquaculture systems practicing different forms of integrated techniques exist; both more extensive traditional systems and the more recently developed intensive systems. Integrated aquaculture is certainly not a panacea for aquaculture development but should be looked upon as one potential tool among many others facilitating sustainable development. These may improve performance with respect to local and regional impacts and from a global resource perspective, and also reduce the vulnerability associated with monoculture. Existing national and international “best management practices”, “codes of conduct”, “development criteria”, etc. developed to guide the industry and individual farmers towards sustainability seem to over-generalise and lead to qualitative goals, without specific means of measurement and monitoring. Sustainability is a broad concept, but even so it needs to be reduced to specific actions to be useful as an objective for ongoing development of aquaculture.

Aquaculture’s potential for development, i.e. its operational space, is rapidly shrinking due to other human activities that either directly or indirectly prevent its prospect (i.e. pollution, space availability, etc.). Some forms of aquaculture may not be fulfilling the many criteria for sustainability (i.e. characterised as “not perfectly responsible aquaculture”) but in some situations, the environmental costs of not developing aquaculture as an alternative livelihood or food provider may be quite high. This is not to say that quick fixes always should be allowed, but that the consequences from inactions need to be analysed from the broader systems perspective.