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By: American Fisheries Society *
Unless urgent action is taken to reduce emissions, scientists predict catastrophic impacts to commercial, recreational, and subsistence fisheries and human health and global economies. This article summarizes key scientific findings highlighting the effect of climate changes on aquatic ecosystems. These findings provide evidence of what effects are currently happening and why world policymakers and all of humankind need to collaborate and launch concerted actions now to mitigate these impacts.
In an unprecedented statement released recently, the American Fisheries Society (AFS) joined forces with 110 aquatic scientific societies representing more than 80,000 scientists worldwide to sound a climate change alarm. The societies call for drastically curtailed global greenhouse gas emissions to avoid the worst impacts of human-made climate change to fish and aquatic ecosystems.
“Climate change is already altering marine and coastal ecosystems with significant implications for wild capture fisheries and marine economies.”
Projected increases in ocean temperature are expected to reduce the maximum catch potential in most areas in the U.S. Many harvested stocks will shift from one area to another, or even across international boundaries, with implications for seafood supply, ports, and associated businesses.
Loss of habitat from sea-level rise will lead to declines in the vast majority of commercially and recreationally harvested marine finfish and shellfish that are dependent on estuaries and coastal systems for some stage of their life cycle.
Increased carbon dioxide absorption is changing ocean chemistry, rendering some waters too acidic for marine organisms with calcium shells, such as oysters and clams, and threatening the base of the marine food web. The impacts of climate change especially threaten freshwater fish.
Forty percent of all in North America are today imperiled due to pollution, habitat loss, water withdrawals, and invasive species. Climate change, coupled with these existing stressors, will lead to significant declines in freshwater fish, with devastating consequences for the cultural, recreational, and economic value of freshwater systems.
“Across the globe, incomes, food security, and aquatic resource-dependent communities’ livelihoods are already at risk. Climate change threatens food security by endangering fish, an essential protein source for many across the globe.”
According to the Food and Agriculture Organization of the United Nations, fish accounts for 17% of animal protein consumed globally, fishing and aquaculture directly employ almost 60 million people, and global trade in fish products has reached US$152 billion per year, with 54% originating in developing countries.
In addition to reductions in emissions, aggressive policies and programs are required to mitigate the effects of climate change to freshwater fish and to preserve habitat essential for resilience.
If we are to avoid losing countless species that provide immeasurable benefits to society, we must also mitigate the impacts of climate change on fish and fisheries and plan for adaptation required to ensure the long-term health of our freshwater, coastal, and marine ecosystems and the many economies that depend upon them.
Intact, healthy habitats can help to provide resilience for fish and store carbon.
“Experts in environmental, social, and economic fields collectively point towards a severe envi-ronmental and humanitarian crisis, with repercussions at a global level, unless worldwide concerted climate actions are implemented urgently.”
This recently published analysis summarizes key scientific findings highlighting the effect of climate changes on aquatic ecosystems. These findings provide evidence of what effects are currently happening and why world policymakers and all of humankind need to act jointly and launch concerted actions if they wish to mitigate these impacts.
The Challenge
Thousands of peer-reviewed studies by scientists from authoritative institutions worldwide have documented evidence for climate effects on aquatic systems that are already occurring and are extensive.
Many globally respected sources, including the American Geophysical Union, National Academies of Science from dozens of countries, the Intergovernmental Panel on Climate Change, and the Fourth U.S. National Climate Assessment support findings that increased atmospheric concentrations of greenhouse gases from fossil fuels (i.e., emissions) and land use changes such as deforestation are driving current climate change.
Many of these changes are and will be irreversible. They will continue to worsen if we persist on our current trajectory.
Impacts already occurring range from increased frequency, intensification, and severity of droughts, heat waves, floods, wildfires, and storms; melting glaciers; destabilization of major ice sheets; shift ing ocean currents, rising sea level; ocean acidification and deoxygenation; shifts in species ranges, including expansion of alien-invasive species; aquatic plant and wildlife disease outbreaks; mass coral bleaching events; and more, with a mounting toll on vulnerable ecosystems, human societies, and local and global economies.
“These events are precursors of even more damages to fisheries, biodiversity, and human society at large. Delaying action to stop the underlying causes of climate change will increase the economic, environmental, and societal consequences.”
Suppose humanity wishes to avoid calamitous consequences for our aquatic ecosystems and humans that depend on them. In that case, the time to curb greenhouse gas emissions, sequester greenhouse gasses, and adapt to an already changing climate is now.
An intelligent, rapid movement toward such goals will provide significant benefits to aquatic ecosystems and the humans that depend on them. Fast global response and large-scale actions are possible if public and government commitment exists.
The Evidence: Effects on Marine Resources
• Shifts in species composition, behavior, abundance, and biomass production are now occurring.
• Lobster, cod, mackerel, coral reef fishes, and other species important to fisheries are either moving poleward to deeper waters or declining.
• Coastal ecosystems are being transformed, degraded, or lost, either largely or in part due to climate change, including seagrass meadows, mangroves, coral reefs, and kelp forests.
• Effects of altered species compositions are affecting entire ecosystems.
• Carbon emissions cause global ocean acidification, which is affecting the survival of organisms, especially shellfish, and accelerating coral reef erosion.
• Rising frequency and intensity of marine heatwaves has been documented and is projected to continue.
• Reductions in global ocean dissolved oxygen concentrations have occurred over the past five decades.
• Climate change is interacting with other stressors such as excess nutrient input, overharvesting, and novel species interactions to further suppress marine ecosystems.
• Climate change is linked to emerging and re-emerging disease outbreaks in marine wildlife and plant species.
• Global production of marine animals continues to decrease, and shifts in species composition will increase unless greenhouse gas emissions are reduced.
• Seabirds are recognized as indicators of long-term environmental change: nearly three out of four of the world’s seabirds have disappeared since 1950, and more than half the remaining species face substantial threats.
In North America alone, two-thirds (389/604) of bird species, including waterbirds, are moderately or highly vulnerable to climate change under a 3°C scenario.
The Evidence: Effects on Freshwater Resources
• Freshwater ecosystems are among the most threatened on Earth. Freshwater ecosystems cover less than 1% of the planet’s surface but support one-third of vertebrate species and 10% of all species.
• The capacity of all freshwater ecosystems to adapt is relatively low, given the nature of freshwater systems and the scale of climate change impacts.
• Climate change is altering abundance, predator-prey dynamics, expansion of invasive species, growth, recruitment of species, and novel species interactions, leading to declines in the number and diversity of freshwater aquatic organisms.
• Increased frequency, intensity, and length of drought affect the amount and quality of freshwater available for both aquatic ecosystems and humans.
• Climate change impacts on flow regimes, including both increased droughts and low-flow periods, and increased flooding impact native species with narrow ranges of flow requirements and allow expansion of alien-invasive species that affect recreational and commercial harvest of fishes and clog waterways.
• Geographic ranges of many plants and animals have moved poleward and to higher altitudes, while alieninvasive species expand with the increasingly warm conditions. Unlike marine systems, pathways to other habitats are often blocked, leading to localized extinctions.
• Temporal shifts in seasonal cues, such as spring runoff or monsoon seasons, affect fish’s spawning success, resulting in poor survival.
• Higher incidence of wildfires is affecting aquatic systems by making watersheds more susceptible to flooding and by reducing water quality, especially with post-fire ash and sediment deposition.
• Wetlands capacity for carbon storage and mitigation of climate change are being damaged by changes linked to climate shifts and other global change components, such as increased land development and fires.
• Higher temperatures and precipitation runoff have increased harmful algae blooms, which can hurt fish, mammals, birds, and even humans.
• Climate change may act synergistically with nutrients to magnify eutrophication and further degrade water quality and ecosystem services, including affecting drinking water.
• Organisms dependent on snowmelt and glacial streams are declining or shifting their distribution.
• Release of heavy metals such as mercury, currently stored in glaciers and the permafrost, is projected to affect freshwater organisms further.
• Climate change is linked to emerging and re-emerging disease outbreaks in freshwater wildlife and plant species.
• These seemingly diverse and smallscale changes combine to create multiple, cumulatively stressful challenges to aquatic species.
The Evidence: Effects on World Society Dependent on Aquatic Resources
• Clean and sufficient water is needed by all life forms.
• Fisheries provide quality protein sources not easily replaced by terrestrial sources. According to the Food and Agriculture Organization of the United Nations, fish accounts for 17% of animal protein consumed globally, fishing and aquaculture directly employ almost 60 million people, and global trade in fish products has reached US$152 billion per year, with 54% originating in developing countries.
• In the short term, new fisheries are appearing in some newly formed icefree areas; however, overall fisheries catch is projected to decline related to increasing declines in water quality and primary production as a result of climate change, with corresponding effects on food security.
Ocean warming and changes in primary productivity are related to changes in many fish stocks. Fish population reestablishment has declined 3% per decade, and maximum catch potential declined 4.1% over the 20th century.
Water temperature increases due to climate change are projected to exceed the tolerance limits of 10–60% of freshwater and marine species by 2100, depending on the amount of greenhouse gas emissions allowed.
• Climate change impacts on aquatic ecosystems affect incomes, food security, key cultural dimensions, and livelihoods of resource-dependent communities.
• Species shifts affect traditional fisheries from the tropics to the polar regions through reduced access to fish stocks, fishing areas, and loss of local knowledge.
• Climate change compounds the impact of other practices such as pollution, overfishing, and unsustainable coastal development. These combined impacts are projected to drive many small-scale fisheries and economies out of existence.
• Warming of waters affects seafood safety through elevated bioaccumulation of heavy metals and pollutants and an increased prevalence of waterborne pathogens affecting both human and animal health.
• Tourism and tourist sites are being affected in many areas that are dependent on local ecosystems. Sustainable diving, snorkeling, angling, marine mammal and bird watching, and other recreational activities and businesses depend on the maintenance of healthy aquatic resources.
• Climate change degrades coastal ecosystems such as mangroves, seagrasses, marshes, peatlands, and coral reefs that provide services to humans, such as protecting coasts from erosion, storms, and flooding, providing key wildlife habitat and sequestering carbon.
• Climate change damages riparian ecosystems that provide services to humans, such as protecting streams from flooding, intercepting pollutants, reducing erosion, providing shade and wildlife habitat, sequestering carbon, and storing water during high-flow events.
• Climate change contributes to harming wetlands, which provide many of the same services to humans, as stated above. Wetlands play a critical role in carbon storage and sequestration. In particular, peatlands, despite occupying on 3% of the land surface, store twice as much carbon as the world’s forests.
• The level of impacts will be governed by the level of protective limits our nations place on future emissions combined with riparian and coastal zoning; and changes in fisheries management practices.
The Needed Responses
We assert that rapid action is necessary to drastically curb release of greenhouse gas emissions and to remove and store CO2 from the atmosphere to prevent the most calamitous consequences of human-caused climate change to marine and freshwater ecosystems on which all humankind depends.
Global and national targets are necessary to protect and restore carbon-dense ecosystems, such as peat, seagrasses, and other wetlands to sequester carbon, prevent greenhouse gas emissions, and reduce climate change impacts.
“Governments, the public, industry, academia, and all other sectors of society must prioritize actions and act in a concerted way to halt humancaused climate change to prevent dire consequences.”
A rapid transition towards energy sources and other products and services that do not release greenhouse gases as well as research and policies that favor an efficient transition to a low carbon world is required to slow the degradation of aquatic systems, as above.
All governments could accomplish such a transition by immediately acting on the advice of specialists in green energy technology, carbon sequestration, marketing, education, socioeconomic principles, and related disciplines.
Robust adaptation measures; identification and easing of other environmental stressors that act synergistically with climate change; and additional resources for data collection, mapping, and research to better understand potential impacts and to arm natural resources agencies with the tools to mitigate these impacts are essential to better understand and plan for changes in aquatic ecosystems.
“Done intelligently, a movement to curtail human-caused climate change can result in advanced, novel technologies; strong economies; healthier aquatic ecosystems; greater food security; and human well-being.”
It is time to acknowledge the urgent need to act to address climate change. Delaying action to control greenhouse gas emissions is not an option if humankind wishes to conserve the world’s aquatic resources and environmental safety.
This is a summarized version of the recently published document from the American Fisheries Society.
References on all evidences found are included on the original article which is available for free at: https://doi.org/10.2989/16085914.2020.1824388 Founded in 1870, the American Fisheries Society (AFS) is the world’s oldest and largest fisheries science society.
The mission of AFS is to improve the conservation and sustainability of fishery resources and aquatic ecosystems by advancing fisheries and aquatic science and promoting the development of fisheries professionals.
With five journals and numerous books and conferences, AFS is the leading source of fisheries science and management information in North America and around the world.
