WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2016 3 Editor’s Note In papers published in Nature and Ecology and Society in 2009 (and since updated), scientists from the Stockholm Resilience Center and elsewhere defined global-scale “planetary boundaries” that establish a “safe operating space” for humanity. The group identified nine planetary boundaries and proposed quantitative limits for most of these. Beyond the planetary boundary is a zone of uncertainty where risks increase until a critical threshold or tipping point is reached. The Earth System processes considered include climate change, change in biosphere integrity (biodiversity), ocean acidification, stratospheric ozone depletion, atmospheric aerosol loading, biogeochemical flows of N and P, freshwater use, landuse change, and chemical pollution. For each process, a control variable is defined as the state of that variable (e.g. atmospheric CO2 concentration, aragonite saturation state, and stratospheric ozone concentration, percentage of cultivated land, maximum amount of annual fresh or blue water use, cumulative P loading to oceans) or the rate of change of the control variable (e.g. extinctions per million species per year, rate of N2 fixed from atmosphere for human use). Processes such as climate change and ocean acidification are systemic processes at a planetary scale, with global-scale thresholds. Others are aggregated from local or regional scales with no known global-scale threshold. Initial elaboration of the planetary boundary concept considered a global scale only, but recent iterations now include consideration of regional scales. Thus, boundaries are now considered at the level of biomes, river basins and areas of intensively developed agriculture. This is in recognition of unequal spatial distribution of contributions to the control variables for each boundary. Based on this framework, humanity has already passed at least three planetary boundaries: the rate of biodiversity loss and changes to biogeochemical flows of P and especially N. We are also rapidly approaching planetary boundaries for land-use change and climate change. Planetary boundaries have obvious implications for global aquaculture. Although aquaculture contributes to the control variable for each planetary boundary, aquaculture is still small relative to other human activities that impact global processes. Perhaps more importantly, aquaculture is being impacted by the anthropogenic changes that lead to transgression of planetary boundaries. Atmospheric CO2 concentration exceeded 400 ppm in 2015 and each month now seems to bring news of a new warmest month on record. The direct and indirect impacts of climate change on aquaculture are too numerous to review in this limited space, but include those related to sea level rise, increased temperature, increased frequency of weather extremes, and disruption in rainfall patterns. Coastal aquaculture infrastructure is highly vulnerable to the risks of climate change. Ocean acidification is considered a planetary boundary distinct from climate change, although the ultimate cause is the same. Currently humanity is below the threshold for serious impacts of ocean acidification, but it remains a matter of great concern for the future of shellfish production. Biogeochemical flows of nitrogen of phosphorus have been altered by fertilizer applications to support agricultural intensification. Relative to natural weathering, there has been a large increase in the flow of nutrients to the oceans, resulting in coastal eutrophication and dead zones of hypoxic water. Coastal aquaculture is impacted by these effects in positive and negative ways. For extractive species, such as bivalve shellfish, coastal eutrophication means that there is more food available to support shellfish production. On the other hand, the quality of water for coastal pond aquaculture has been degraded by eutrophication. The effect of changes in biodiversity on aquaculture is difficult to assess. Of the nine planetary boundaries assessed, this has been exceeded by the greatest extent. Extinction rates are thought to be weak metrics to evaluate the boundary of biodiversity loss. Alternative approaches include phylogenetic diversity leading to long-term resilience, functional diversity of traits in ecosystems and biome condition or security to avoid tipping points. Other planetary boundaries have a strong effect on biodiversity and this may be the importance of its role in maintaining a safe operating space for humanity. Beyond this, maintaining reservoirs of genetic diversity of the major (and emerging) culture species is an important reason to maintain biodiversity. The Blue Oceans report estimated that increasing aquaculture production to 100 million t by 2030 will increase environmental impacts by 2-2.5 times, compared to 2008 levels, with the greatest environmental footprint associated with carp production in ponds in China and elsewhere in Asia. The contributions of aquaculture to global CO2 emissions can be reduced by improving energy efficiency in production and across the value chain. The environmental impact of aquaculture can be improved by reducing dependence on fishmeal, increasing feed conversion efficiency and developing innovative feeding practices. Implementing better management practices can increase the efficiency of natural resources used to support aquaculture production. Some might look at the concept of planetary boundaries and ask what is new here? After all, we’ve had The Limits to Growth from 1972 and ecological footprint accounting from the early 1990s. The concept of carrying capacity is inherent in aquaculture production itself and in the Ecological Approach to Aquaculture advocated by the FAO. The planetary boundaries concept puts quantitative limits on global processes. The insight of this framework for aquaculture, and all human activity for that matter, is to establish priorities for high-level, global-scale institutions, governance and actions to stay within the safe space. Future growth in global aquaculture will need to take explicit limits of key processes at global, regional and local scales into account. — John A. Hargreaves, Editor-in-Chief Planetary Boundaries and Aquaculture
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