The ocean is becoming more acidic worldwide as a result of increasing atmos-pheric concentrations of carbon dioxide (“CO2”) and other pollutants. This fundamen-tal change is likely to have substantial ecological and economic consequences globally.In this Article, we provide a toolbox for understanding and addressing the drivers ofocean acidification. We begin with an overview of the relevant science, highlightingknown causes of chemical change in the coastal ocean. Because of the difficulties asso-ciated with controlling diffuse atmospheric pollutants such as CO2, we then focus oncontrolling smaller-scale agents of acidification, discussing ten legal and policy toolsthat state government agencies can use to mitigate the problem. This bottom-up ap-proach does not solve the global CO2 problem, but instead offers a more immediatemeans of addressing the challenges of a rapidly changing ocean. States have amplelegal authority to address many of the causes of ocean acidification; what remains is toimplement that authority to safeguard our iconic coastal resources.

What is Ocean Acidification?

Ocean acidification is a reduction in the pH1 of seawater for an extended period of time due primarily to the uptake of carbon dioxide from the atmosphere by the ocean. Local sources of acidification such as nitrogen oxides and sulfur oxide gases, or nutrients and organic carbon from wastewater discharges and runoff from land-based activities, can also contribute to ocean acidification in marine waters.

As the level of atmospheric carbon dioxide (CO₂) continues to rise, so too does the amount of CO₂ in the ocean (1, 2), which increases the ocean's acidity. This affects marine ecosystems on a global scale in ways we are only beginning to understand: for example, impairing the ability of organisms to form shells or skeletons, altering food webs, and negatively affecting economies dependent on services ranging from coral reef tourism to shellfish harvests to salmon fisheries (3–5). Although increasing anthropogenic inputs drive acidification at global scales, local acidification disproportionately affects coastal ecosystems and the communities that rely on them. We describe policy options by which local and state governments—as opposed to federal and international bodies—can reduce these local and regional “hot spots” of ocean acidification.

Marine calcifiers, especially those in their larval and juvenile stages, are thought to be most vulnerable to ocean acidification (OA) due to the effects of carbon dioxide (CO2) on growth and shell mineralogy. However, recent evidence is contradictory. We monitored molting activity, length and weight in early benthic phase (EBP, Wahle 1992) American lobster Homarus americanus (Milne-Edwards 1837) under elevated CO2 conditions (500 μatm, 1100-1300 μatm, and 2000-2700 μatm) to determine how OA affects growth at this life stage. Molted shells were analyzed for magnesium (Mg2+) and calcium (Ca2+) content by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Exposure to higher CO2 partial pressures over a 90-120 day period affected intermolt period length and caused decreased length and weight growth increments. The higher concentrations of CO2 also changed the magnesium to calcium (Mg:Ca) ratio present in the mineralized shell. Shells from lobsters in the medium and high CO2 treatments had an overall higher Mg:Ca than lobsters in the control CO2 treatment, which can have consequences for shell dissolution in higher CO2 conditions. Lobsters in the medium and high CO2 treatments were also more susceptible to shell disease compared to those in the low CO2 treatments. Taken together, these results suggest juvenile EBP lobsters may remain smaller for a longer period of time, which could make them more vulnerable to disease and/or shell dissolution in a high CO2 ocean.

An organism’s physiological processes form the link between its life-history traits and the prevailing environmental conditions, especially in species with complex life cycles. Understanding how these processes respond to changing environmental conditions, thereby affecting organismal development, is critical if we are to predict the biological implications of current and future global climate change. However, much of our knowledge is derived from adults or single developmental stages. Consequently, we investigated the metabolic rate, organic content, carapace mineralization, growth, and survival across each larval stage of the European lobster Homarus gammarus, reared under current and predicted future ocean warming and acidification scenarios. Larvae exhibited stage-specific changes in the temperature sensitivity of their metabolic rate. Elevated Pco₂ increased C∶N ratios and interacted with elevated temperature to affect carapace mineralization. These changes were linked to concomitant changes in survivorship and growth, from which it was concluded that bottlenecks were evident during H. gammarus larval development in stages I and IV, the transition phases between the embryonic and pelagic larval stages and between the larval and megalopa stages, respectively. We therefore suggest that natural changes in optimum temperature during ontogeny will be key to larvae survival in a future warmer ocean. The interactions of these natural changes with elevated temperature and Pco₂ significantly alter physiological condition and body size of the last larval stage before the transition from a planktonic to a benthic life style. Thus, living and growing in warm, hypercapnic waters could compromise larval lobster growth, development, and recruitment.

Trends of increasing temperatures and ocean acidification are expected to influence benthic marine resources, especially calcifying organisms. The European lobster (Homarus gammarus) is among those species at risk. A project was initiated in 2011 aiming to investigate long-term synergistic effects of temperature and projected increases in ocean acidification on the life cycle of lobster. Larvae were exposed to pCO2 levels of ambient water (water intake at 90 m depth, tentatively of 380 μatm pCO2), 727 and 1217 μatm pCO2, at temperatures 10 and 18 °C. Long-term exposure lasted until 5 months of age. Thereafter the surviving juveniles were transferred to ambient water at 14 °C. At 18 °C the development from Stage 1 to 4 lasted from 14 to 16 days, as predicted under normal pH values. Growth was very slow at 10 °C and resulted in only two larvae reaching Stage 4 in the ambient treatment. There were no significant differences in carapace length at the various larval stages between the different treatments, but there were differences in total length and dry weight at Stage 1 at 10 °C, Stage 2 at both temperatures, producing larvae slightly larger in size and lighter by dry weight in the exposed treatments. Stage 3 larvae raised in 18 °C and 1217 μatm pCO2 were also larger in size and heavier by dry weight compared with 727 μatm. Unfortunate circumstances precluded a full comparison across stages and treatment. Deformities were however observed in both larvae and juveniles. At 10 °C, about 20% of the larvae exposed to elevated pCO2were deformed, compared with 0% in larvae raised in pH above 8.0. At 18 °C and in high pCO2 treatment, 31.5% of the larvae were deformed. Occurrence of deformities after 5 months of exposure was 33 and 44% in juveniles raised in ambient and low pCO2, respectively, and 20% in juveniles exposed to high pCO2. Some of the deformities will possibly affect the ability to find food, sexual partner (walking legs, claw and antenna), respiration (carapace), and ability to swim (tail-fan damages).

Ocean acidification resulting from the global increase in atmospheric CO2 concentration is emerging as a threat to marine species, including crustaceans. Fisheries involving the American lobster (Homarus americanus) are economically important in eastern Canada and United States. Based on ocean pH levels predicted for 2100, this study examined the effects of reduced seawater pH on the growth (carapace length) and development (time to molt) of American lobster larvae throughout stages I–III until reaching stage IV (postlarvae). Each stage is reached after a corresponding molt. Larvae were reared from stage I in either acidified (pH = 7.7) or control (pH = 8.1) seawater. Organisms in acidified seawater exhibited a significantly shorter carapace length than those in control seawater after every molt. Larvae in acidified seawater also took significantly more time to reach each molt than control larvae. In nature, slowed progress through larval molts could result in greater time in the water column, where larvae are vulnerable to pelagic predators, potentially leading to reduced benthic recruitment. Evidence was also found of reduced survival when reaching the last stage under acidified conditions. Thus, from the perspective of larval ecology, it is possible that future ocean acidification may harm this important marine resource.

Global warming and increased atmospheric co 2 are causing the oceans to warm, decrease in pH and become hypercapnic. These stressors have deleterious impacts on marine inver-tebrates. Increasing temperature has a pervasive stimulatory effect on metabolism until lethal levels are reached, whereas hypercapnia has a narcotic effect. ocean acidification is a major threat to cal-cifying larvae because it decreases availability of the carbonate ions required for skeletogenesis and also exerts a direct pH effect on physiology. Marine invertebrate propagules live in a multistressor world and climate change stressors are adding to the mix. ocean pH, pco 2 and caco 3 covary and will change simultaneously with temperature, challenging our ability to predict future outcomes for marine biota. To address questions of future vulnerabilities, data on the thermo-and pH/pco 2 tolerance of fertilization and development in marine invertebrates are reviewed in the context of the change in the oceans that are forecast to occur over the next 100–200 years. Gametes and fertilization in many invertebrates exhibit a broad tolerance to warming and acidification beyond stressor values projected for 2100. Available data show that all development stages are highly sensitive to warming. larvae may be particularly sensitive to acidification/hypercapnia. Embryos that develop through the bottleneck of mortality due to warming may succumb as larvae to acidification. Early juveniles may be vulnerable to skeletal dissolution, although warming may diminish the negative impact of acidifi-cation on calcification. The effects of climate change stressors and their interaction differ among life history stages and species. Multistressor experiments show that if thermal thresholds are breached, embryos may not reach the calcifying stage. If the bottleneck for species persistence is embryonic thermotolerance, then the question of compromised calicification due to acidification may not be relevant. our limited knowledge of the interactive effects of climate change stressors is a major knowledge gap. Although climate change is deleterious for development in a broad range of marine invertebrates, some species and regional faunas will be more resilient than others. This has implica-tions for persistence, faunal shifts, species invasions and community function in a changing ocean.

Oceanic uptake of anthropogenic CO2 results ina reduction in pH termed “Ocean Acidification” (OA). Com-paratively little attention has been given to the effect of OAon the early life history stages of marine animals. Conse-quently, we investigated the effect of culture in CO2-acidifiedsea water (approx. 1200 ppm, i.e. average values predictedusing IPCC 2007 A1F1 emissions scenarios for year 2100)on early larval stages of an economically important crus-tacean, the European lobster Homarus gammarus. Culture in CO2-acidified sea water did not significantly affect carapacelength of H. gammarus. However, there was a reduction incarapace mass during the final stage of larval development in CO2-acidified sea water. This co-occurred with a reductionin exoskeletal mineral (calcium and magnesium) content ofthe carapace. As the control and high CO2treatments were not undersaturated with respect to any of the calcium carbon-ate polymorphs measured, the physiological alterations werecord are most likely the result of acidosis or hypercapnia interfering with normal homeostatic function, and not a di-rect impact on the carbonate supply-side of calcification perse. Thus despite there being no observed effect on survival,carapace length, or zoeal progression, OA related (indirect) disruption of calcification and carapace mass might still ad-versely affect the competitive fitness and recruitment successof larval lobsters with serious consequences for population dynamics and marine ecosystem function.