Aquaculture is one of the human activities that has accelerated the most in the last half of the century. However, climate change and other constraints will undoubtedly challenge future growth of marine aquaculture. It is, therefore, critical to anticipate new opportunities and challenges in marine aquaculture production during the Anthropocene.
The environmental effect of human activity is increasing at unprecedented rates and at a global scale. At a conference in Mexico in 2000, Paul Crutzen, winner of the Nobel Prize in Chemistry, expressed the idea that we have entered a new geological epoch driven by the impact of human activities on the Earth System: the Anthropocene.
Marine aquaculture, which is focused mainly on aquatic plants, mollusks, and to a lesser extent fish, now accounts for almost half of global aquaculture production, recently exceeding wild capture fisheries.
Temperature and sea-level rise, shifts in precipitation, freshening from glacier melt, changing ocean productivity and circulation patterns, increasing occurrence of extreme climatic events, eutrophication, and ocean acidification (OA) are some of the stressors that will influence the potential of marine aquaculture production.
In this context, the ICES Journal of Marine Science (IJMS) solicited contributions to the themed article set (TS), “Marine aquaculture in the Anthropocene”. The objective of this TS was to bring together contributions on the broad theme of the potential impacts, adaptation, and mitigation strategies of marine aquaculture in an era of rapid change.
Impacts of climate change-related factors on aquaculture production and spatial distribution of species-specific aquaculture activities
Human activities are estimated to have caused ~1ºC of global warming above pre-industrial levels. The oceans are not only absorbing a large amount of heat, leading to ocean warming, but also about 25% of anthropogenic CO2 emissions. Increasing CO2 concentrations in the atmosphere lower the pH of the oceans, a process referred to as OA.
The pH in the ocean’s surface waters has already decreased by 0.1 units since the beginning of the Anthropocene. Simultaneously, aqueous CO2 concentrations are increasing, and carbonate ion concentrations are decreasing, possibly impacting the growth, physiological rates, immune
responses, behavior, and survival of some marine organisms.
“Scientists have conducted many OA experiments, usually exposing organisms to experimental conditions based on scenarios modelled for oceanic waters, typically simulating present and near-future ocean pCO2 levels.”
However, most marine organisms are cultivated in coastal areas such as intertidal and upwelling zones, estuaries, fjords, and salt marshes where pH/ pCO2 levels vary far more dramatically than in the open ocean. Such variability in coastal environments limits the relevance of applying predictions of CO2 in the open ocean to these situations. Also, coastal aquaculture is likely to be affected by OA in different ways than open-ocean aquaculture. Our knowledge of the variability in pH and carbonate chemistry in coastal areas is relatively poor and predictions are lacking.
In bivalves, embryonic and larval development are generally sensitive to OA, with reductions in size and survival of larvae and increases in the number of abnormal larvae. On an industrial scale, the most striking illustration of possible OA effects is the correlation between the pH of seawater and the survival of oyster larvae, clearly linking the pHT/ pCO2 of seawater to hatchery failures Phenotypic plasticity and adaptation potential of farmed species under climate change, including selective breeding for resilience. Carryover effects can occur between development stages, but also between generations (intergenerational effects). For instance, exposure of adults to OA can produce positive or negative carryover effects in their progeny that influences survival under conditions of lower pH.
Adaptation to OA will ultimately depend on trade-offs that occur when a relationship between two traits prevents them from being simultaneously optimized. For example, a population might possess genetic variation for tolerance to both OA and disease, but if there is a negative correlation between these two traits it may not be possible to evolve substantially increased tolerance to OA and disease simultaneously.
The effect of climate change-related drivers on species interactions: the intricate cases of parasitism and predation
Climate change can alter host–pathogen interactions and, therefore, the likelihood of disease outbreaks. For instance, interactions between hosts, pathogens, and the environment govern disease outbreaks, and a change in any of these components can shift the balance towards or away from a highintensity disease state. Temperature is the most well-studied climate-related driver of marine disease because it profoundly influences host and pathogen metabolism. Although there are reports of the exacerbating effects of temperature on the risk of disease, it is difficult to attribute a causal link between climate change and the occurrence of disease.
Salmon farms act as reservoirs of sea lice that are a source of transmission from farmed to wild salmon. Considering that temperature increases the epidemic potential of the parasite. Rapid increase in salmon
farming has dramatically altered the disease dynamics between farmed and wild salmon. In Norway, new restrictions on fish farming have been enforced in the south due to the impacts of sea lice on wild salmonids.
“In northern areas, the effects of pathogens on wild salmonids are lower, reflecting relatively low density of fish farms and low temperatures. However, both factors are now increasing. These areas contain habitats supporting some of the largest remaining wild salmonid populations in the world.”
Temperature can differentially influence species within a community, significantly affecting the outcome of trophic interactions. For example, ocean warming is predicted to strengthen plant–herbivore interactions and potentially impact seaweed production. Warming increases the consumption rate of herbivores and also, the palatability of macroalgae. This effect might be tempered by other factors such as nutrient availability.
Adaptive measures for mitigate the impacts of climate change on marine resources
The combined accelerated footprint of climate change and anthropogenic pressures on marine life raise the need for restoration programs worldwide.
Rinkevich (2021) analyzes the recent literature on coral reef restoration from an ecological engineering perspective, linking biology, ecology, and engineering to improve and rehabilitate damaged ecosystems. He concludes that ecological engineering should consider creating new ecosystems that did not exist before rather than seeking to recreate historic ecosystem states.
In a literature review, Daly et al. (2021) investigated the implications of phenotypic plasticity for enhancement of crustacean stocks. The main idea is that there are behavioral and morphological differences between hatchery-raised and wild individuals that reflect adaptive responses to an unnatural rearing environment, and this phenotypic plasticity could be used to improve stock enhancement.
Sustainable development of aquaculture and its contribution to climate change
Concerns over the footprint of the ever-expanding aquaculture industry have motivated a range of approaches focusing on aquaculture impact analysis.
Kluger and Filgueira (2021) argue that carrying capacity should be viewed as multidimensional, iterative, inclusive, and just. Hence, the scope of carrying capacity needs to move from industry-driven towards an inclusive vision taking into consideration historical, cultural, and socio-economic concerns of all stakeholders.
The cultivation and use of seaweeds have high potential to support sustainable jobs and growth, providing biomass for human food, animal feed, and other applications like climate remediation. Although the large majority of seaweed production is located in Asia, interest in Europe is on the rise.
Van den Burg et al. (2021) show that, from a people, planet and profit perspective, the focus is not on producing large volumes of seaweed but on producing the right amount of the right seaweeds, considering the carrying capacity of European seas.
“Finally, Froehlich et al. (2021) ask how the 20 International Council for the Exploration of the Sea (ICES) member nations will sustainably meet the increasing demand for seafood, considering that the majority of these nations have not developed robust aquaculture industries.”
They found that the majority of ICES nations lack long- term strategies for aquaculture, with few plans accounting for climate change and an increasing gap between future production and consumption.
This work highlights the need to prioritize aquaculture policy to set more ambitious domestic production goals and improve sustainable sourcing of seafood from other parts of the world, with a more explicit incorporation of climate change into decision-making.
Summary and forward look
From all these articles and the associated scientific literature, it seems that three types of action are possible for adapting aquaculture operations to climate change. First, we must anticipate the biogeographical changes in the distribution of species. Species are indeed distributed over geographic areas where physical and biotic conditions fit their physiological range and any changes in these conditions may locally alter the potential for aquaculture production. Second, we must determine whether species can adapt to a variety of stressors through evolution.
Then, the selection of robust phenotypes, which are resistant or tolerant to these stressors would be an option for the aquaculture industry, although trade-off with other traits and maintaining the genetic diversity need to be carefully considered. Third, we must consider ecosystem conservation, restoration, or remediation strategies to foster resilience to climate change stressors. Biodiversity indeed limit disease risk, an upcoming threat under climate change.
“Macroalgae and plant act as a carbon sink and create local refugia against acidification for calcifying organisms. These examples suggest that the combination of species that interact favorably with each other can mitigate the effects of climate change. These three options are not mutually exclusive and should be considered together.”
Not all aquaculture productions are created equal. For example, intensive culture of shrimp or carnivorous fish is highly energy demanding, while production of omnivorous fishes, bivalve mollusks or macroalgae have a low or even negative carbon footprint. Therefore, aquaculture will undoubtedly contribute to the low carbon economy of tomorrow. Development choices should be based on carbon footprint and product LCAs in addition to traditional profitability analyses. Aquaculture can help make our planet great again, this is a matter of choice.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “THE FUTURE IS NOW: MARINE AQUACULTURE IN THE ANTHROPOCENE” developed by: FABRICE PERNET, AND HOWARD I. BROWMAN.
The original article was published on FEBRUARY 2021, through INTERNATIONAL COUNCIL FOR THE EXPLORATION OF THE SEA under the use of a creative commons open access license.