The Journal of the World Aquaculture Society (JWAS) is a special publication among the aquaculture l...
Climate change: Response and role of global aquaculture
Climate change is a reality and both an immediate and future threat to global food security. A multitude of climatic aberrations are occurring in aquatic and terrestrial environments and are linked to the accumulation of greenhouse gases, much arising from human activity. Altered biotic and abiotic conditions of both terrestrial and marine‐based production systems are appearing at a much faster rate than earlier projected. Disruptions in the availability of food derived from these systems are inevitable consequences, and most probably will warrant changes in traditional eating habits of global ethnic populations.
Examples of the effects of climate change are extreme weather events causing water shortages and agricultural crop failures, ocean warming and acidification, sea level rise, adverse changes in water quality, sediment loading, or rapid fluctuations in salinity (Lesk, Rowhani, & Ramankutty, 2016; Rutkayova et al., 2018). A rapid halt to these changes is not realistic, yet passive acceptance is not an option. Policy and behavioral reality at national and international scales indicate that causes and adverse consequences of climate change are unlikely to be limited during the forthcoming decades and will ultimately require effective efforts devoted to mitigation and adaptation. The “political will to fight climate change is fading” as the UN Secretary General Guterres stated this past May, and the 31 years of inaction because of the phenomenon of climate change entered global knowledge would indicate that political will perhaps reflects a fading will of humankind. Public education and overwhelming advocacy for expeditious action are essential, but often difficult to inspire as the effects of the phenomenon develop and intensify gradually, and thus are not perceived as an immediate crisis, or a crisis at all. Global action requires the need to recognize the distressing consequences of the changes that are occurring, including impacts on traditional forms of economic development.
Aquaculture has been identified and welcomed as an important “remedy” to successfully address the challenges to global food security arising from climate change and intensified by the projected 2050 world population of 9.5 billion (National Research Council, 2015). Yet, the “solutions” applied to the rapid expansion of global aquaculture will most probably encounter setbacks and even impediments specific to the conditions caused by climate change itself (Callaway et al., 2012). Productivity of marine ecosystems is projected to decrease at mid and low latitudes and correspondingly increase at high latitudes (Barange et al., 2014). In fact, reductions of primary production of oceans are estimated to reach 6% by 2100, 11% in tropical areas (FAO, 2018). Populations of marine organisms will undergo changes in density and geographic distribution and fishery yields will fall (Perry, Low, Ellis, & Reynolds, 2005; Plaganyi, 2019). With potential declines in the rate of cultured seafood production and the annual volume of capture fisheries, efforts to provide sufficient seafood for human consumption will be tested.
During the first decade of the 21st century, published reports (FAO, 2009; Handisyde, Ross, Badjeck, & Allison, 2006) synthesized results of particular investigations to offer descriptions of scenarios arising, both directly and indirectly, from climate change. Potential impacts on physical and biological variables were described with emphasis on such topics as biodiversity, disease, and the availability of fishmeal. In addition, the carbon footprint contribution of aquaculture to global warming was evaluated and possible solutions toward its mitigation were presented.
Current sites of marine aquaculture locations will definitely be subject to continued changes in physical properties such as temperature, salinity, sea level rise, and increased storm activity, thereby affecting species growth and survival and even continued operational viability. Freshwater, on‐land production units, commonly ponds, will be subject to vagaries in the amount and quality of the freshwater resource (including flooding) as well as temperature extremes. In those production systems where manufactured feed is necessary, vacillations or absences of important feed ingredients derived from terrestrial production or marine capture fisheries may result, consequently requiring a change to the use of other ingredients as components of effective aquafeeds.
The control required to respond to climate change relative to providing the projected demand for seafood protein principally resides in culture rather than capture fisheries. If global aquaculture production is to be maintained and possibly increased, adaptive responses need to be defined, complete with detailed plans for possible future implementation. Currently used production systems will have to evolve, leading to new approaches to management practices that are based on possible changes in behavioral and other physiological responses as abiotic and biotic conditions become subject to change and resources decline. Long‐term studies that monitor environmental variables are critical to the development of responsive management strategies, and the assessment of long‐term changes in alkalinity of inland waters (Somridhivej & Boyd, 2017) is an excellent example. Complementary knowledge derived from investigations that specifically address physiological responses to changes are critical. For example, Realis‐Doyelle, Pasquet, Fontaine, and Teletchea (2018) evaluated the role of water temperature on early life stages of common carp based on projections of increasing water temperature of freshwater ecosystems caused by climate change. Thus, multiple paths that would contribute to aquaculture enterprise successfully meeting the challenges do exist.
Results of recent investigations have identified regions where marine aquaculture production is postulated to be positively and negatively affected, and accordingly the need to develop strategies to maintain or exceed production levels and thus meet the global seafood demands in 2050 was emphasized (Froehlich, Gentry, & Halpern, 2018). In concert with the global movement toward the predominant use of renewable energy in the future, what knowledge, derived from research, coupled with technological development, is needed to implement reactive and proactive management strategies to enhance sustainable production? What more might aquaculture contribute?
In the following sections, we address research and development requirements that will be the foundation of successful adaptation whereby current production levels can be maintained and hopefully increased. We also speculate about whether aquaculture can play an even greater role in mitigation, if appropriate political will and human endeavor prevail.
1 SPECIES THERMAL BIOLOGY
Precise understanding of thermal physiology of all major aquaculture species is essential to maintain growth and survival in warming seas. Energy allocation changes rapidly in response to increasing temperature, altering physiological responses such as growth, survival, behavior, and reproduction. Susceptibility to facultative pathogens increases as animals reach temperature limits. Reduced growth at a “stressful” temperature is less likely to capture headlines than mass die‐offs at extremes, but more likely to markedly reduce food production. Thus, there is a critical need for investigations that yield data to allow the prediction of expected changes in growth and survival in response to water temperature increases in key aquaculture regions. An understanding of performance changes under interactive stressors, such as temperature anomalies combined with salinity drops, is also required, particularly in application to risk management. Adaptive needs and strategies (new species selection, production period shifts, new site selection, technological/closed solutions) can then be appropriately assessed and implemented for the key species and identified site. This research must also encompass the qualitative and quantitative incidence of parasites and pathogens under future climate models, including temperature extremes (Oldham, Rodger, & Nowak, 2016).
2 SELECTIVE BREEDING AND SHIFTING SPECIES
Next‐generation sequencing, genotyping, and phenotyping allow rapid identification of desirable traits for most cultured species. Research seeking expanded tolerances (temperature, salinity, etc.) is necessary to select lines that will perform better under permanently altered growing conditions. For those situations where tolerances of all lines are exceeded, the solution may reside in the farming of alternative species at existing production sites. Applied research that identifies most favorable alternative species to replace excluded species is needed. This management approach has been successfully applied in many pond systems in the past, but commonly in response to populations of a given species being devastated by disease. Where possible, production methods for economically viable alternative species should be fully researched and established before species shifts are put into effect.
3 SHIFTING PRODUCTION PERIODS AND IMPLEMENTING ALTERNATIVE METHODS
For species with a short production cycle, a seasonal change in the production period may offer opportunity to produce animals before temperature extremes become limiting. This shifting requires complementary research to develop methods to reliably produce or collect larvae, spat, or fingerlings when they are commonly unavailable so that challenges posed by stocking under different grow‐out conditions are overcome. For species with production periods of 12 months or more, this option is not feasible, and if sites are to be maintained, then technological solutions must be developed to maintain production during periods of adverse, possibly lethal temperatures. Intricate solutions, such as transportable/temporary recirculating aquaculture systems that achieve water cooling in freshwater ponds or at nearshore sites, would require large‐scale investments and could possibly eliminate cost‐effectiveness. The option of emergency cooling systems for large‐scale ponds seems to be impractical and energy inefficient; however, such large‐scale technical solutions may prove viable if used to overcome short‐term extreme events. A less complex solution for marine species would be a mechanism whereby sea cages could be lowered to deeper and cooler water during periods of extreme temperature. Implementation of short‐term technological solutions for production systems must still constructively fulfill the ever‐present, underlying goal of minimizing the level of risk.
4 SHIFTING PRODUCTION SITES
Marked poleward movement of site selection for salmonid farming, particularly for new development in Chile and Norway, indicates that marine aquaculture producers are already heeding predicted polar shifts for marine species in response to increases in water temperature (Perry et al., 2005). This strategic action is risky as temperature shifts can be less predictable than expected, underscoring the need for accurate models derived from long‐term data collection in advance of the establishment of new production sites (Shears & Bowen, 2017). The complex nature of temperature and precipitation shifts under global warming scenarios highlight the importance of enhanced interaction with marine spatial planning and modeling, and confirms the need for specialist research dedicated to future optimization of aquaculture site selection. Having the luxury of maintaining multiple sites for a production cohort is unlikely; however, analysis of the potential value of “emergency cooling sites” for short‐term holding of animals during weather extremes is worthy of research. The continued development and testing of viable offshore solutions are key areas of research to ensure growth in the production of suitable species under conditions resulting from climate change. Offshore and deeper waters in the marine environment are less susceptible to temperature and salinity extremes than in nearshore sites. Nonetheless, success in offshore aquaculture enterprise will definitely require unique engineering applications to address the increased incidence of potentially catastrophic storm events.
5 OTHER POSSIBILITIES WITH POTENTIAL APPLICATION
Unique and unexplored strategies for adaptation and mitigation may evolve. Research focus may be directed to determine whether formulations of manufactured aquafeeds can be developed to aid animals in overcoming physiological challenges posed by a changing climate, co‐cultures or integrated multitrophic aquaculture (IMTA) systems that are more resilient to change, or the presence of certain species that can favorably protect others from environmental extremes.
6 THE ROLE OF AQUACULTURE IN MITIGATING CLIMATE CHANGE
Aquaculture already holds a substantive mitigating role in the struggle to cope with the adverse effects of climate change. If the appropriate species and production systems are applied, the protein derived from aquaculture animal products is commonly associated with the lowest carbon output with the added advantage of zero methane emissions and low land‐use cost (Flachowsky, Meyer, & Sudekum, 2018). Additionally, global macroalgae and bivalve farming already uptake nearly a million tons of carbon from the sea per annum (Turan & Neori, 2010). The open ocean offers the only available area for large‐scale sequestration of carbon as well as the natural capacity to uptake significantly more via macroalgae and other extractive species. If efficiently cultured en masse, the propagation of suitable extractive species, particularly macroalgae, has the potential to completely mitigate human CO2 emissions within an area of 35–50 million ha, a fraction of the 1,040 million ha currently used in agriculture (International Energy Agency, 2018). To remove that level of carbon will require a process for sequestration in the abyssal regions of the oceans. Such large‐scale undertakings may indeed prove successful, but may concomitantly result in unexpected and/or undetected modifications of the deep ocean or other marine environments.
7 THE QUANDARY ABOUT THE PATH TO SOLUTION
The research needs and alteration of management practices that we have proposed raise serious questions about whether aquaculture should support “geoengineering,” i.e., the deliberate manipulation of environmental systems to combat the effects of global warming. What has been presented should invoke serious contemplation about whether such extreme measures are a product of the mind‐set that sees these solutions as simply offering humankind the opportunity to continue to demand “everything for everyone until everything is simply gone” or whether the urgent threat of climate change truly warrants geoengineering. Open ocean farming, together with massive reforestation efforts, may offer realistic solutions to global atmospheric carbon excesses. Nonetheless, humankind may also be better served by answering more pressing questions about itself, individually and as a whole, to find long‐term solutions to climate change.
Regardless of ideology, aquaculture enterprise plays an integral role in contributing to global food security, human nutrition, international trade, and economic development and status. Agencies within those countries that predominantly contribute to the carbon footprint need to act wisely and duly fund education, training, and research that is founded in the pivotal role of aquaculture enterprise in mitigation of and adaptation to the disruptive effects of global climate change. Engagement and principled follow‐through at the level of international policy are essential. Funded research now and in the future must be a product of the recognition of the specific need for knowledge that can be successfully applied to aquaculture's reactive and proactive response. The Journal of the World Aquaculture Society welcomes submissions of research results of investigations that are relevant to the vital role of aquaculture in response to mitigation of the effects of climate change and adaptation as necessary. These investigations may include recommendations for assessment and contain or lead to allied plans of action.
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About Louis R. D'Abramo, Matthew J. Slater
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