Probing Human Vulnerability to Ocean Acidification Uncovers Mitigation and Adaptation Opportunities

Ocean acidification has recently elbowed its way onto the list of wicked problems that coastal communities need to plan for.

Sarah Cooley, Ocean Conservancy
Julia Ekstrom, U. California Davis
Lisa Suatoni, Natural Resources Defense Council

Ocean acidification has recently elbowed its way onto the list of wicked problems that coastal communities need to plan for. Coastal communities depend on a variety of oceanic goods and services, often led by marine harvests [1]. However, ocean acidification is poised to disrupt this dependence: for example, it jeopardized the Pacific Northwest United States’ shellfish industry for multiple years when upwelling waters soured by ocean acidification killed millions of oyster larvae [2]–[4]. Carbon dioxide released into the atmosphere by burning fossil fuels dissolves in seawater, adding even more carbon dioxide to what’s naturally in the water. This extra carbon dioxide changes seawater’s acidity and carbonate ion balance [5].

Pacific oysters are not the only organism harmed by ocean acidification, though. Many types of mollusks, corals, crustaceans, and coralline algae grow more slowly or die [6]–[10] due to ocean acidification, and squid [11]–[13], crustaceans [14]–[16] , and finfish and sharks [17]–[21]  experience changes in metabolism, immunity, olfaction, or behavior that are likely to affect the animals’ chances of survival.

Coastal human communities also are threatened by ocean acidification. Communities dependent on shellfish harvests may be harmed most by the loss of shellfish. Some people will have more capacity than others to prevent or deal with economic hardship from such losses.  In recent studies, we have focused on these factors to explore the risk that ocean acidification poses to human communities via shellfish harvests [22], [23]. Combining what we know about the biological response of shellfish, the dependency of coastal communities on shellfish and the capacity of these communities, we can start to show which communities might feel effects via harvests sooner and worse than others. “Hotspots” are high risk areas where ocean acidification overlaps with other oceanographic and coastal factors that exacerbate it, where humans harvest a great deal of shellfish for income or nutrition, and where communities are less equipped to deal with a shock to the system that disrupts this productivity [22], [23]. This approach is commonly used at early stages of climate adaptation processes worldwide for assessing vulnerabilities and risks from climate change [24]. There is currently no way to forecast with high accuracy exactly when or where acute harm from ocean acidification will hit next. Instead, we must rely on risk-based assessments that use information about current patterns of human dependence on harvests of vulnerable species and that assume future dependence will be similar, even though oceanic conditions are changing.

Applying this approach has already shown us that census areas and boroughs in southeastern and southwestern Alaska are at greater risk than other areas in the state [22] (Figure 1). This overall risk comes from the regions’ high number of rural communities that get both commercial harvesting income and subsistence-based nutrition from shellfish harvests, yet do not have many alternatives for other jobs or foods. These factors make overall risks higher for southeastern and southwestern Alaska even though ocean acidification is changing water chemistry faster near Bering Strait and North Alaska communities. This study’s results showed that examining oceanographic factors alone is not enough to grasp how human communities could be harmed by ocean acidification.

Figure 1:  Vulnerability of Alaska census areas and boroughs (reddish tones) to ocean acidification. Top panel shows how economic impacts from shellfish harvesting vary across the state, and bottom panel shows how subsistence harvesting of shellfish varies across the state, both superimposed over the total vulnerability measure. The total vulnerability measure takes into account economic and nutritional dependence, as well as oceanographic and social details that vary statewide. Reprinted from NOAA Climate.gov, based on analysis by Mathis et al. [22].

Figure 1: Vulnerability of Alaska census areas and boroughs (reddish tones) to ocean acidification. Top panel shows how economic impacts from shellfish harvesting vary across the state, and bottom panel shows how subsistence harvesting of shellfish varies across the state, both superimposed over the total vulnerability measure. The total vulnerability measure takes into account economic and nutritional dependence, as well as oceanographic and social details that vary statewide. Reprinted from NOAA Climate.gov, based on analysis by Mathis et al. [22].

In a second study examining shellfish harvests and ocean acidification, we assessed the risk of coastal areas across the entire United States. In this study we included additional oceanographic factors and different economic and cultural information [23]. In addition to mapping how ocean acidification from atmospheric carbon dioxide is likely to proceed, we also noted locations of upwelling currents, eutrophication (algal overgrowth linked to nutrient runoff, which can die, rot, and intensify ocean acidification) and acidification-enhancing river runoff (where large river discharge provides low-pH, low-carbonate-ion water to the coastal zone and adds to ocean acidification’s effects). We combined information showing where communities depend on shellfish harvests with indicators of a region’s depth of resources for handling a disruption (e.g., presence of alternative local shellfish species, access to scientific information about ocean acidification). When mapped, these data showed that there is no single place in the United States at risk from all of the factors we evaluated (Figure 2). Instead, many coastal communities are exposed to and exhibit a unique combination of risk factors that make them susceptible to harm from ocean acidification via lost shellfish harvests.

Figure 2: Overall vulnerability of U.S. regions to ocean acidification. Social vulnerability is shown on land, in red tones, and severity of ocean acidification (purple) and its local amplifiers (algal overgrowth, in yellow stars  and “E( x/y)”; low-pH river discharge, yellow triangles and “R (x/y)”; upwelling, “U”) is shown over the water. E(x/y) notes the number of highly eutrophic estuaries (x) relative to the total number of estuaries evaluated in each region (y), while R(x/y) notes the number of rivers with low carbonate ion levels and high annual discharge volume (x) relative to the total number of rivers in a region (y). Darker colors indicate higher vulnerability or hazard. Purple scale indicates the year at which average ocean chemistry will reach a lethal level for larval shellfish. Reprinted from Ekstrom et al. [23] with permission of Nature Climate Change.

Figure 2: Overall vulnerability of U.S. regions to ocean acidification. Social vulnerability is shown on land, in red tones, and severity of ocean acidification (purple) and its local amplifiers (algal overgrowth, in yellow stars and “E( x/y)”; low-pH river discharge, yellow triangles and “R (x/y)”; upwelling, “U”) is shown over the water. E(x/y) notes the number of highly eutrophic estuaries (x) relative to the total number of estuaries evaluated in each region (y), while R(x/y) notes the number of rivers with low carbonate ion levels and high annual discharge volume (x) relative to the total number of rivers in a region (y). Darker colors indicate higher vulnerability or hazard. Purple scale indicates the year at which average ocean chemistry will reach a lethal level for larval shellfish. Reprinted from Ekstrom et al. [23] with permission of Nature Climate Change.

Despite the discouraging news that so many regions in the U.S. are vulnerable to ocean acidification, we see the study’s results as hopeful. A wider range of solutions may exist than anyone previously expected to prepare coastal communities for a future including ocean acidification. One approach is to reduce the local contributors that are increasing acidification. Communities seeking to address other coastal environmental problems such as nutrient pollution have more incentive to do so. Another approach may be to reduce economic dependency on susceptible species. Communities seeking to sustain or diversify local fisheries may choose to explore aquaculture that boosts populations of native shellfish species or restores key habitats supporting local shellfish populations. Yet another approach may seek to increase people’s capacity to adapt to or mitigate the impacts of ocean acidification. Communities wishing to deepen knowledge about ocean acidification and innovative solutions may choose to strengthen links between local shellfish industries and researchers. In every community, though, a different combination of adaptation options is likely to be most suitable, given cultural, environmental, and economic factors [23].

Vulnerability studies have great promise for shedding light on the regionally variable relationships that coastal communities have with each other and with their coastal zones. For an issue like ocean acidification, where  acute impacts have yet to be felt in most locations, risk and vulnerability assessments including social and ecological factors can suggest potential opportunities for preventative action. Effective actions will reduce current vulnerabilities and thus help avoid potentially disastrous impacts. Planning ahead is key. As the old saying goes, “forewarned is forearmed.” Vulnerability studies offer powerful guidance for decision-makers thinking about ocean acidification to assess the issue and its local implications. With these types of results in hand, taking targeted, preventive action is now possible.

Author Bios

Sarah Cooley, Ph.D., is the science outreach manager in the ocean acidification program at Ocean Conservancy. Originally a carbon cycle scientist, her research focuses most recently on the human implications of ocean acidification and policy opportunities to address the issue.

Julia Ekstrom, Ph.D., is the climate adaptation program director at University of California, Davis. As a social scientist, she conducts social vulnerability assessments and research related to communities preparing for, coping with and adapting to climate change.

Lisa Suatoni, Ph.D., is a senior scientist in the oceans program at the Natural Resources Defense Council, and she specializes on the intersection of science and policy, as it applies to ocean conservation. She has been working on the science and policy of ocean acidification over the past five years.

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