Anticipating ocean acidification's economic consequences for commercial fisheries

Sarah R Cooley^,2 and Scott C Doney

Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

² Address for correspondence: Woods Hole Oceanographic Institution, Clark, MS #25 Woods Hole, MA 02543, USA

E-mail: scooley@whoi.edu

Received 14 January 2009
Accepted 8 May 2009
Published 1 June 2009

Contents

• 1. Introduction
• 2. Ocean acidification and marine organisms
• 3. Economic consequences for US commercial fisheries
• 4. Management implications
• Acknowledgments
• References

1. Introduction

Intensive fossil-fuel burning and deforestation over the last two centuries have increased atmospheric CO₂ by almost 40% above preindustrial values to levels higher than at any time over the past 800 000 years or longer (Doney and Schimel 2007). Future projections suggest even more rapid CO₂ accumulation unless dramatic actions are taken to curb human CO₂ emissions. The global ocean currently absorbs  ~ 30% of the released anthropogenic CO₂ (Sabine et al 2004, Denman et al 2007), fundamentally altering ocean chemistry by acidifying surface waters (Caldeira and Wickett 2003) and shrinking ocean regions hospitable to calcium carbonate (CaCO₃) shells and skeletons (Orr et al 2005, Feely et al 2008). Ongoing ocean acidification thus may harm a wide range of marine organisms and the food webs that depend on them, thereby degrading entire marine ecosystems (Fabry et al 2008, Doney et al 2009). Laboratory studies suggest that mollusks, including species that support valuable marine fisheries such as mussels and oysters (Gazeau et al 2007), and especially their juveniles (Kurihara et al 2007, 2009, Cohen 2008, Barton 2009), are particularly sensitive to these changes. Societies dependent on marine calcifiers could consequently experience significant economic losses and even social disruptions over the next several decades. In this study, we begin to constrain the potential economic effects of ocean acidification using US commercial fishery revenues from 2007 as a case study, focusing especially on mollusks. We also identify implications for marine resource management and review possible adaptation strategies designed to support fisheries and marine-resource-dependent communities.

2. Ocean acidification and marine organisms

The oceanic uptake of anthropogenic CO₂ occurs through a series of well-known chemical reactions that increase aqueous CO₂, lower seawater pH, and lower carbonate ion levels. To date, anthropogenic CO₂ has reduced average surface ocean pH to 8.1 from a preindustrial value of 8.2, a 30% increase in acidity (Caldeira and Wickett 2003). Equally important for marine life, acidification decreases carbonate concentration and thus the saturation state of CaCO₃ minerals in the upper ocean (Ω). The projected increase in anthropogenic CO₂ emissions over the next 50 years, primarily associated with industrial growth in developing nations, will accelerate ocean chemistry changes to rates unprecedented in the recent geological record (figure 1; Doney et al 2009, Doney and Schimel 2007). Model-predicted atmospheric CO₂ trajectories increase from  ~ 385 ppm in 2008 to 450–650 ppm by 2060 (IPCC 2001), which would decrease average ocean surface pH by an additional 0.2–0.3 units (to an average of 7.9–7.8) and reduce the saturation states of calcite (Ω_ca) and aragonite (Ω_ar) by  ~ 25% (figure 1), further shrinking optimal regions for biological carbonate formation (Steinacher et al 2009). Seasonal acidification events are already appearing; water with Ω_ar < 1 (undersaturated or corrosive conditions) upwells along the California coastline in summer, decades earlier than models predict (Feely et al 2008). Also, some high-latitude polar and subpolar waters may see Ω_ar ~ 1 by mid-century or earlier (Orr et al 2005, Steinacher et al 2009). Worse, average forecasts may even be somewhat conservative; estimated fossil-fuel CO₂ emissions in 2005 exceeded those predicted by the most extreme scenario from the 1990s (A1FI in figure 1; Raupach et al 2007), implying that future atmospheric CO₂ levels may exceed current model predictions, and the oceans may acidify faster than presently forecast.

Organisms' net responses to rising CO₂ will vary depending on often opposing sensitivities to decreased seawater pH, carbonate concentration, and carbonate saturation state, and to elevated oceanic total inorganic carbon and gaseous CO₂. Shell-forming marine organisms create carbonate structures using one of two approaches. Detailed reviews can be found in Fabry et al (2008), Doney et al (2009). Briefly, organisms that exert low biological control over calcification directly deposit CaCO₃ along their inner shell walls, and consequently, they depend on a sufficient ambient carbonate concentration to accumulate shells successfully. Commercially valuable mollusks such as bivalves (e.g., scallops, oysters) and some gastropods (e.g., conchs) use this method to build shells. Shells deposited in this manner are more likely to contain aragonite, a more soluble mineral form of CaCO₃. Corals form aragonite skeletons extracellularly, while coralline algae secrete aragonite or magnesian calcite, a moderately soluble form of CaCO₃. Organisms that exert high biological control over calcification typically accumulate intracellular stocks of carbonate ions gradually and harden their chitin and protein exoskeletons by depositing CaCO₃ from within, usually in the less soluble form of calcite. Sea urchins and crustaceans, including lobsters, shrimp, and crabs, follow this model and therefore require less specific seawater chemistry to form shells. Animals' ultimate responses may also depend on less easily quantified factors such as individual history or genetic variability (Doney et al 2009).

Ocean acidification and declining carbonate concentration could directly damage organisms, specifically corals and mollusks, by decreasing calcification rates. Reduced calcification is observed in response to rising CO₂ and declining carbonate concentration even in waters that are thermodynamically supersaturated for calcium carbonate (Ω decreasing but still above 1). Many organisms, some commercially valuable, also exhibit a range of negative consequences for metabolism, reproduction, development, intracellular chemistry, and immunity (e.g., Fabry et al 2008, Holman et al 2004, Burgents et al 2005, and references therein) (table 1). Acidification's effects on fishes' ability to grow internal carbonate structures for feeding and migration such as otoliths, statoliths, and gastroliths are still unknown. On the other hand, some planktonic organisms, crabs, lobsters, shrimp, and other organisms increase calcification or photosynthesis in high- CO₂ seawater (Ries et al 2008a, 2008b, Doney et al 2009). Whether the observed examples of increased calcification or photosynthesis under high- CO₂ conditions result in enhanced species fitness is not yet known. But decreases in calcification and biological function seem very capable of decreasing fitness of commercially valuable groups, like mollusks, by compromising early development and survival (e.g., Kurihara et al 2007, 2009) or by directly damaging shells (e.g. Gazeau et al 2007).

Ocean acidification's total effects on the marine environment will depend also on ecosystem responses. Even if carbonate-forming organisms can form shells and skeletons in elevated- CO₂ conditions, they may pay a high energetic cost (Wood et al 2008) that could reduce survival and reproduction (Kleypas et al 2006). Losses of plankton, juvenile shellfish, and other prey also would alter or remove trophic pathways and intensify competition among predators for food (Richardson and Schoeman 2004), potentially reducing harvests of economically important predators. At the same time, acidic conditions will damage coral and prevent its regrowth, destroying crucial benthic habitats and disrupting hunting and reproduction of an array of species (Kleypas et al 2006, Lumsden et al 2007). Ecological shifts to macroalgal overgrowth and decreased species diversity sometimes follow after coral disturbances (Norström et al 2009), creating stable new ecosystem states (Scheffer et al 2001) dominated by herbivores (Hoegh-Guldberg et al 2007) and less commercially valuable species. Ocean acidification has been implicated in similar ecological shifts from calcifying organisms to seagrasses and algae in wild benthic communities with decreasing pH (Hall-Spencer et al 2008, Wootton et al 2008).

3. Economic consequences for US commercial fisheries

Ocean acidification may affect humans through a variety of socio-economic connections, potentially beginning with reduced harvests of commercially important species. The total ex-vessel or primary value of US commercial harvests from US waters and at-sea processing was nearly $4 billion in 2007 (all monetary values given in US dollars) (figure 2; NMFS statistics, http://www.st.nmfs.noaa.gov/st1/index.html, and Andrews et al 2008). Of the total, mollusks provided 19% (red tones), crustaceans yielded 30% (yellows), and finfish generated 50% (greens); 24% of total US ex-vessel revenue was from harvesting fish that prey directly on calcifiers. The supplementary information lists the NMFS-tracked species included in each category. Different groups dominate regional revenues; mollusks are more important in the New England and mid to south Atlantic regions (figure 2), crustaceans contribute greatly to New England and Gulf of Mexico fisheries, and predators dominate the Alaskan, Hawaiian, and Pacific-territory fisheries.

Nationwide, income and jobs generated by US fisheries multiply dramatically from catch to retail sale. In 2007, domestic commercial fisheries, harvest from outside US territories, and aquaculture provided a primary sale value of $5.1 billion (table 2; all dollar values in this paper are in 2007 dollars unless otherwise indicated). Processing, wholesale, and retail activities led to sales of $68.3 billion, contributing $34.2 billion in value added to the US gross national product in 2007 (Andrews et al 2008). The number of individuals employed directly and indirectly by commercial fishing is difficult to quantify, because fishermen are frequently self-employed; furthermore, middlemen who do not handle solely ocean products are not counted in industry surveys. In the United States, commercial fish processing and wholesaling together supported 63 000 jobs in 2007 (Andrews et al 2008). For perspective, in 1999, commercial fishing employed 10 500 people in New York State, wholesale and processing supported 5060 jobs, and retail sales supported an additional 10 100 jobs. Seafood sales at New York restaurants supported the equivalent of 70 000 full-time jobs. In total, the seafood industry supported nearly 100 000 jobs in New York State (New York Sea Grant 2001).

Supplementing the economic benefit from commercial fishing, US recreational fishing encourages spending on permits, equipment, and travel, and in support industries, thereby generating jobs, profits, tax revenues, and business-to-business revenue. In 2000 (the latest date for which data is available), recreational saltwater fishing generated $12 billion of income in the United States (Steinback et al 2004) and supported almost 350 000 jobs, for a total economic benefit of $43 billion that year (table 2).

Ocean acidification's impact is not yet known for every commercially and recreationally valuable species, but emerging data suggest that the number or quality of many high-value, aragonite-forming mollusks could decrease, and declining economic revenues in that fishery sector may follow. This possibility is supported by findings such as decreased mollusk populations in acidified ecosystems (Wootton et al 2008, Hall-Spencer et al 2008), malformation of juvenile oyster shells in aragonite-undersaturated laboratory studies (Cohen 2008), and decreased survival of oyster larvae in upwelling Oregon seawater with decreased pH and altered biogeochemistry (Barton 2009). Mollusks and crustaceans comprise the bottom or middle trophic levels of many ecosystems, implying that acidification-related damage to either of these groups also may negatively impact their primary and secondary predators (Fredriksen et al 2007, Richardson and Schoeman 2004). Effects of prey losses on predator numbers are poorly quantified at present, however, and the total ecosystem impact will depend on whether alternative prey species are available and whether predators can switch among prey. Currently, predictions of ex-vessel losses from declining mollusk harvests must depend on translating laboratory experiments showing damage to individual organisms into population losses in nature. To our knowledge, there have been no experimental results published in the literature to date that quantitatively link calcification decreases or organism mortality to decreasing saturation state in a natural environment. Nevertheless, existing data do permit estimating potential first-order losses associated with ocean acidification.

To provide a starting point for discussing ocean acidification's economic impact on mollusks, we assume a simple one-to-one correspondence between reduced calcification for a particular atmospheric CO₂ level and reduced commercial mollusk harvests. We construct future harvest trends using IPCC atmospheric CO₂ trajectories and the laboratory results of Gazeau et al (2007), who observed 10–25% decreases in mollusk calcification rates at CO₂ ~ 700 ppm (pH ~ 7.9–8.0, Ω_ar ~ 2, and Ω_ca ~ 3). Atmospheric CO₂ of 700 ppm occurs by 2060 in a high-CO₂ emissions world (A1FI; figure 1) and after 2100 in a low- CO₂ emissions world (B1). This assumed relationship, although certainly imperfect and preliminary, generates results broadly consistent with the limited available field data. Here, harvest decreases of 6%–25% (B1, low rate–A1FI, high rate) accompany 0.1–0.2-unit pH decreases over 50 years (2010–2060), whereas Wootton et al (2008) observed a 10%–40% decrease in calcifying organism cover associated with a 0.4-unit pH decrease over just 8 years in a natural coastal lagoon environment.

As is clear from the temporal mismatch between our model and field observations, our assumptions cannot completely address the complexity that will dictate ocean acidification's total economic effects. We assume no regional variations in acidification, and we neglect potentially significant changes in commercial fishing from consequences for crustaceans, trophic cascade changes involving predators and finfish, finfish larvae damage, or coral reef habitat losses. By highlighting just mollusk fisheries, our projections may in fact underestimate fisheries impacts if the effects of acidification occur more broadly across ecosystems. These ecosystem-scale responses are outside the scope of this study, yet are expected to greatly shape outcomes by guiding individual species responses; Wootton et al (2008) note that the significant community shift they observed was likely a function of multiple ecosystem factors and not just declining calcification or organism health. Furthermore, biological studies have not yet quantitatively identified ameliorative long-term processes that could offset losses, like natural selection of resistant species or strains, or initiation of self-defensive strategies. For the economic projections, we also make no assumptions about changes in fishing intensity or the effects of supply and demand on marine resource prices.

Here, we calculate potential revenue losses from decreased mollusk harvests in the future, adjust to present-day values using a range of net discount rates (0%, 2% and 4%), and integrate over time to provide estimates of net present value (NPV); anticipated future revenue losses are worth less than losses today because of the compounding effects of interest and capital return rates. Mollusks accounted for $748 million (19%) of 2007 US domestic ex-vessel revenues, with an NPV (assuming no changes from present ecological and economic conditions from today) integrated to mid-century (2007–2060) of roughly $17–40 billion depending on the applied discount rate. If just a 10–25% decrease in US mollusk harvests from 2007 level were to occur today, $75–187 million in direct revenue would be lost each year henceforth, with a net NPV loss of $1.7–10 billion through mid-century.

A more realistic scenario would involve more gradual annual revenue declines with increasing atmospheric CO₂ and acidification. Table 3 provides estimates of the NPV of revenue losses for the US mollusk fishery through 2060 for varying discount rates, high- CO₂ and low-CO₂ atmospheric trajectories, and the upper/lower bounds from Gazeau et al (2007) experiments to constrain the range of biological responses (–10% to –25% for Ω_ar ~ 2 or  ~ 700 ppm CO₂). For a moderate net discount rate of 2%, the NPV of US ex-vessel revenue losses are substantial: $0.6–2.6 billion through 2060. The NPV or revenue loss is also sensitive to future atmospheric CO₂ trajectories and thus to decisions about CO₂ emissions; the high-CO₂ scenario losses are almost 1.7 times larger than those for the low- CO₂ scenario, and this factor continues to grow with longer time horizons. These revenue losses would be unevenly distributed, being nearly four times higher in mollusk-dependent New England than in the Pacific.

The broader economic effects of reduced mollusk harvests due to ocean acidification are more difficult to quantify, but we may be able to illustrate the potential effects through some simple economic comparisons and calculations. Economic losses from harmful algal blooms (HABs), whose damage to lower trophic levels and cascading economic consequences may resemble those of ocean acidification, cost the United States an average of $12 million each year (in 2000 dollars) by causing human sickness, fish mortality, decreased demand for fish products, habitat loss, damage to fisheries valuable in the future, and depressed recreation and tourism (Hoagland et al 2002). In certain well-studied markets, broader shellfish economic losses resulting from HABs have been estimated with an economic multiplier of 2.0–3.0 (Hoagland et al 2002). Multiplying the NPV of declining mollusk ex-vessel revenues associated with ocean acidification estimated above by an intermediate value of 2.5 indicates that the time-integrated NPV of ocean acidification's broader economic losses for the United States would range from $1.5–6.4 billion through 2060 for a 2% discount. However, the magnitude of economic multipliers may change in the future if market conditions vary significantly from those used to develop the multiplier (Hoagland et al 2002); net present value also neglects the effects of supply and demand on marine resources. Fishery losses due to ocean acidification will drive job losses in affiliated industries through economic linkages that are also difficult to quantify.

Uncertainties in biological responses to ocean acidification also contribute to the range of anticipated economic impacts. Calcification rates of some calcifiers, like corals, decrease much more dramatically than those reported by Gazeau et al (2007) for oysters and mussels, causing noticeable degradation at lower CO₂ levels than assumed above; populations or ecosystems may also exhibit collapses or shifts above a CO₂ threshold rather than undergo a slow decline (e.g., Norström et al 2009). Alternatively, our calculations may be overestimates if species can adapt to gradual change (Boyd et al 2008) and commercial harvests shift to more abundant or acidification-resistant species over time. Studies of ecological shifts on perturbed coral reefs, for example, suggest that herbivorous species like parrotfish (e.g., Hoegh-Guldberg et al 2007) may thrive in future non-coral-dominated reef communities. Currently the US commercial market for parrotfish is quite small—in 2007 ex-vessel revenues were only $161 000 (NMFS statistics)—but future abundance does not necessarily imply increased market interest. Refining economic loss estimates depends on better understanding marine responses to ocean acidification, accounting for adaptation or conservation measures enacted in the next 50 years, and correctly predicting market responses to fishing changes (Hoagland et al 2002).

Secondary economic losses following decreased fishery harvests will be concentrated in specific regions, many of which have less economic resilience for enduring losses of fishing revenues. For example, New Bedford, MA, has historically relied on fishing income and currently hosts a large scallop fleet. In 2007, its mollusk-dominated ex-vessel revenues were $268 million, making New Bedford the top American port in terms of landing revenues (NMFS statistics). A 25% loss from ocean acidification would decrease landing revenues by $67 million a year or cause an NPV loss of $2.2 billion through 2060 (2% net discount); the more conservative acidification scenario presented above would result in an NPV of direct revenue losses of $546–916 million (table 3), followed by spiraling costs associated with indirect socio-economic losses. Already, the seafood products employment sector in New Bedford decreased 25% from 1992–1999; fishing-related declines also affect wholesale, some retail sales, and transportation (Center for Policy Analysis 2001). Certainly, any economic losses could harm this region, where 20% of the population in 1999 fell below the poverty line (compared to 9% statewide and 11% nationwide that year; US Census data) and where the income gap separating the highest- and lowest-income families is growing at the sixth fastest rate nationwide (Gittell and Rudokas 2007a, 2007b, Center for Policy Analysis 2001). Economic changes resulting from fishery losses in a city like New Bedford could continue to alter its dominant economic activities and demographics, and further accelerate the income gap's development.

4. Management implications

The only true solution or mitigation option for ocean acidification is limiting fossil-fuel CO₂ emissions to the atmosphere (Pacala and Socolow 2004), a long-term goal that requires a fundamental reorganization of energy and transportation infrastructures worldwide. Climate geoengineering approaches that do not control atmospheric CO₂ will not address acidification (Zeebe et al 2008). Because ocean acidification's seawater chemistry changes are already apparent and will grow over the next few decades (e.g., Feely et al 2008), short-term responses intended to conserve sustainable marine environmental resources should also focus on adaptation to the inevitable near-future CO₂ increases. Addressing the global problem of ocean acidification with the goal of preserving commercially valuable fisheries resources will require regional solutions. Some local-scale strategies, like enhanced electrochemical weathering (House et al 2007), directly combat seawater ocean acidification by increasing alkalinity, but such methods would likely be expensive and energy intensive for a small benefit. Other strategies, like updating fishery management plans to include acidification, are less costly and can be regionally tailored as needed to accommodate biological, economic, and social variations.

Designing new policies must begin with comprehensive research targeted towards regional needs (Doney et al 2009). First, expanded time series studies of coastal and open-ocean seawater chemistry are needed to monitor ocean acidification's progress and place it in context with historical data. Second, basic studies at the organism level are required to enhance our currently limited knowledge of commercial and keystone species' responses to decreased pH and elevated CO₂. Topics of particular interest include the roles that life history and population variability may play in shaping acidification responses and the sensitivity of mollusk, crustacean, and finfish larvae, juveniles, and adults to changing seawater chemistry. Third, ecosystem-wide studies are needed to shed light on secondary effects from habitat and prey losses; such information will be particularly useful for fisheries dominated by predatory finfish, like the US Pacific regions, where the relative effects of prey switching, keystone species change, benthic and habitat degradations, and overall biomass reduction must be understood for long-term planning. Biological research results will enable managers to identify and aid regionally valuable species better; for example, research might suggest adjustments to fishery quotas or marine protected areas, show that aquaculture of juvenile mollusks is warranted along some coastlines, or that preservation of a particular keystone predator would keep some crustacean fisheries robust. Fourth, economic and social science studies are needed to understand better how markets, prices, and communities will respond to declining fishery harvests and how best to mitigate potential socio-economic impacts.

For improved long-range planning, quantitative assessments of marine organisms' responses to ocean acidification and climate change must be explicitly incorporated into fishery management plans. Mathematical fisheries models should be enhanced with chemistry and temperature-driven climate change and acidification terms, based on species-specific observational studies, to help determine appropriate harvest levels for many fisheries. Such model refinement would help ensure that catch levels remain sustainable despite ongoing environmental changes. However, the likelihood of complex secondary effects resulting from ocean acidification emphasizes the need for developing and using ecosystem-based management models. More accurate predictions of ocean acidification's regional economic effects would arise from bioeconomic models adjusted for ocean acidification and climate change, enabling timely implementation of fiscally sound responses.

Fishery management and conservation should also enable sufficient proportions of non-commercial species to survive changing ocean chemistry and any ensuing ecological shifts so that fundamental ecosystem function and services are preserved (Costanza et al 1997). Following a precautionary approach to management, fishing pressure reduction and environmental stress minimization should therefore begin before ocean acidification's effects on marine resources become obvious and perhaps irreversible. The consequences of a precautionary approach could decrease fishery revenues in the short term, but such a conservation strategy may in fact result in greater fish stocks and higher revenues in the long run when economic discounting and sustainable yields are included (Costanza et al 1997). Adjusting fishery management plans must take into account not only economic considerations, but also biological or conservation goals and social outcomes, like community preservation (Charles 2007).

An `objectives-based' approach to addressing ocean acidification can help balance both ecosystem and social objectives through adjusting fishing pressure (Charles 2007). Decreasing fishery capacity by reducing external pressures and conserving the marine environment may involve license or vessel buyouts, or regional fishery closures of varying durations. Increasing fishery capacity could involve encouraging multi-species fishing, developing new markets, minimizing waste, increasing aquaculture, or supporting research to select for less pH- and Ω-sensitive species or strains. However, shifting fishing activities via these methods while avoiding widespread unemployment also requires coupled labor market adjustments such as retraining fishers and rewarding job transitions. Furthermore, social measures must be pursued to support marine-resource-dependent communities, which may experience changes in demographics, community organization, livelihoods, local economies, generational roles, and government involvement during the shift.

A particular difficulty that managers face in addressing ocean acidification is its long timescale, creating the illusion that this very urgent problem can be handled later. On the contrary, the slow recovery of the earth system from rapid atmospheric CO₂ increases (Andrews et al 2008) means that CO₂ emissions to date will continue to alter ocean chemistry in the foreseeable future. Ocean acidification meanwhile will drive biological changes apparent over  ~ 50 years and economic effects that will compound over time; note the potential for time-integrated NPV of ex-vessel revenue losses to increase 30–300%, depending on discount rate, from 2060 to 2100 (table 3). Reducing CO₂ emissions over the next few decades, despite incurring small up-front costs, could consequently provide noticeable economic benefits over the next several generations (Stern Review 2006).

The worldwide political, ethical, social, and economic ramifications of ocean acidification, plus its capacity to switch ecosystems to a different state following relatively small perturbations, make it a policy-relevant `tipping element' of the earth system (Lenton et al 2008). Because the fate of this tipping element will be decided within the century, policies should address ocean acidification quite soon. Complicating the development of comprehensive responses is the intermediate timescale over which ocean acidification operates: longer than multiyear adaptive fishery management plans, but shorter than decades-to-centuries CO₂ mitigation plans. The uncertainty of whether ocean acidification's effects will appear incrementally or after dramatic ecosystem reorganizations also hinders planning. Despite these drawbacks, regional-scale marine resource management plans must begin now to estimate the scope of ocean acidification's consequences, and these short-term efforts must be followed by long-term CO₂ mitigation plans to continue progress.

The present assessment only focuses on the United States and excludes economic consequences for coral ecosystems (see treatments in, e.g., Cesar et al 2002, Burke et al 2004), but the effects of ocean acidification will be global. Marine resources are important food supplies that provide 20% of the world's protein (FAO 2007), distributed unevenly around the world. Some developing island and coastal nations that depend heavily on marine and coral ecosystems for food, tourism, and exportable natural resources stand to suffer the most economically (Stern Review 2006) from the consequences of ocean acidification and climate change. As rising sea levels physically endanger these communities, ocean acidification may decrease their food supplies. Additionally, coral damage will expose low-lying coastline communities and diverse mangrove ecosystems to storm and wave damage, increasing the potential for economic and social disruption following severe weather events. Fortunately, the chemistry of ocean acidification is predictable, which allows us to anticipate its effects and enact management plans that will protect the United States' economic interests and provide strategies helpful for other nations.

Acknowledgments

We thank P Hoagland, D Jin, and H Kite-Powell for helpful discussions, and we are grateful for the insightful suggestions of J Guinotte, E Miles, A Murawski, A Solow, and an anonymous reviewer. This work was supported by NSF grant ATM-0628582.

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