Impact of Ocean Warming and Ocean Acidification on Larval Development and Calcification in the Sea Urchin Tripneustes gratilla

Background

As the oceans simultaneously warm, acidify and increase in P _CO2, prospects for marine biota are of concern. Calcifying species may find it difficult to produce their skeleton because ocean acidification decreases calcium carbonate saturation and accompanying hypercapnia suppresses metabolism. However, this may be buffered by enhanced growth and metabolism due to warming.

Methodology/Principal Findings

We examined the interactive effects of near-future ocean warming and increased acidification/P _CO2 on larval development in the tropical sea urchin Tripneustes gratilla. Larvae were reared in multifactorial experiments in flow-through conditions in all combinations of three temperature and three pH/P _CO2 treatments. Experiments were placed in the setting of projected near future conditions for SE Australia, a global change hot spot. Increased acidity/P _CO2 and decreased carbonate mineral saturation significantly reduced larval growth resulting in decreased skeletal length. Increased temperature (+3°C) stimulated growth, producing significantly bigger larvae across all pH/P _CO2 treatments up to a thermal threshold (+6°C). Increased acidity (-0.3-0.5 pH units) and hypercapnia significantly reduced larval calcification. A +3°C warming diminished the negative effects of acidification and hypercapnia on larval growth.

Conclusions and Significance

This study of the effects of ocean warming and CO₂ driven acidification on development and calcification of marine invertebrate larvae reared in experimental conditions from the outset of development (fertilization) shows the positive and negative effects of these stressors. In simultaneous exposure to stressors the dwarfing effects of acidification were dominant. Reduction in size of sea urchin larvae in a high P _CO2 ocean would likely impair their performance with negative consequent effects for benthic adult populations.     

The stunting effect of a high CO2 ocean on calcification and development in sea urchin larvae,a synthesis from the tropics to the poles

The stunting effect of ocean acidification on development of calcifying invertebrate larvae has emerged as a significant effect of global change. We assessed the arm growth response of sea urchin echinoplutei, here used as a proxy of larval calcification, to increased seawater acidity/pCO₂ and decreased carbonate mineral saturation in a global synthesis of data from 15 species. Phylogenetic relatedness did not influence the observed patterns. Regardless of habitat or latitude, ocean acidification impedes larval growth with a negative relationship between arm length and increased acidity/pCO₂ and decreased carbonate mineral saturation. In multiple linear regression models incorporating these highly correlated parameters, pCO₂ exerted the greatest influence on decreased arm growth in the global dataset and also in the data subsets for polar and subtidal species. Thus, reduced growth appears largely driven by organism hypercapnia. For tropical species, decreased carbonate mineral saturation was most important. No single parameter played a dominant role in arm size reduction in the temperate species. For intertidal species, the models were equivocal. Levels of acidification causing a significant (approx. 10–20+%) reduction in arm growth varied between species. In 13 species, reduction in length of arms and supporting skeletal rods was evident in larvae reared in near-future (pCO₂ 800+ µatm) conditions, whereas greater acidification (pCO₂ 1000+ µatm) reduced growth in all species. Although multi-stressor studies are few, when temperature is added to the stressor mix, near-future warming can reduce the negative effect of acidification on larval growth. Broadly speaking, responses of larvae from across world regions showed similar trends despite disparate phylogeny, environments and ecology. Larval success may be the bottleneck for species success with flow-on effects for sea urchin populations and marine ecosystems.     

The Response of Antarctic Sea Ice Algae to Changes in pH and CO2

Ocean acidification substantially alters ocean carbon chemistry and hence pH but the effects on sea ice formation and the CO₂ concentration in the enclosed brine channels are unknown. Microbial communities inhabiting sea ice ecosystems currently contribute 10–50% of the annual primary production of polar seas, supporting overwintering zooplankton species, especially Antarctic krill, and seeding spring phytoplankton blooms. Ocean acidification is occurring in all surface waters but the strongest effects will be experienced in polar ecosystems with significant effects on all trophic levels. Brine algae collected from McMurdo Sound (Antarctica) sea ice was incubated in situ under various carbonate chemistry conditions. The carbon chemistry was manipulated with acid, bicarbonate and bases to produce a pCO₂ and pH range from 238 to 6066 µatm and 7.19 to 8.66, respectively. Elevated pCO₂ positively affected the growth rate of the brine algal community, dominated by the unique ice dinoflagellate, Polarella glacialis. Growth rates were significantly reduced when pH dropped below 7.6. However, when the pH was held constant and the pCO₂ increased, growth rates of the brine algae increased by more than 20% and showed no decline at pCO₂ values more than five times current ambient levels. We suggest that projected increases in seawater pCO₂, associated with OA, will not adversely impact brine algal communities.     

Responses of the Metabolism of the Larvae of Pocillopora damicornis to Ocean Acidification and Warming

Ocean acidification and warming are expected to threaten the persistence of tropical coral reef ecosystems. As coral reefs face multiple stressors, the distribution and abundance of corals will depend on the successful dispersal and settlement of coral larvae under changing environmental conditions. To explore this scenario, we used metabolic rate, at holobiont and molecular levels, as an index for assessing the physiological plasticity of Pocillopora damicornis larvae from this site to conditions of ocean acidity and warming. Larvae were incubated for 6 hours in seawater containing combinations of CO₂ concentration (450 and 950 µatm) and temperature (28 and 30°C). Rates of larval oxygen consumption were higher at elevated temperatures. In contrast, high CO₂ levels elicited depressed metabolic rates, especially for larvae released later in the spawning period. Rates of citrate synthase, a rate-limiting enzyme in aerobic metabolism, suggested a biochemical limit for increasing oxidative capacity in coral larvae in a warming, acidifying ocean. Biological responses were also compared between larvae released from adult colonies on the same day (cohorts). The metabolic physiology of Pocillopora damicornis larvae varied significantly by day of release. Additionally, we used environmental data collected on a reef in Moorea, French Polynesia to provide information about what adult corals and larvae may currently experience in the field. An autonomous pH sensor provided a continuous time series of pH on the natal fringing reef. In February/March, 2011, pH values averaged 8.075±0.023. Our results suggest that without adaptation or acclimatization, only a portion of naïve Pocillopora damicornis larvae may have suitable metabolic phenotypes for maintaining function and fitness in an end-of-the century ocean.     

Hypoxia and Acidification Have Additive and Synergistic Negative Effects on the Growth,Survival, and Metamorphosis of Early Life Stage Bivalves

Low oxygen zones in coastal and open ocean ecosystems have expanded in recent decades, a trend that will accelerate with climatic warming. There is growing recognition that low oxygen regions of the ocean are also acidified, a condition that will intensify with rising levels of atmospheric CO₂. Presently, however, the concurrent effects of low oxygen and acidification on marine organisms are largely unknown, as most prior studies of marine hypoxia have not considered pH levels. We experimentally assessed the consequences of hypoxic and acidified water for early life stage bivalves (bay scallops, Argopecten irradians, and hard clams, Mercenaria mercenaria), marine organisms of significant economic and ecological value and sensitive to climate change. In larval scallops, experimental and naturally-occurring acidification (pH, total scale  = 7.4–7.6) reduced survivorship (by >50%), low oxygen (30–50 µM) inhibited growth and metamorphosis (by >50%), and the two stressors combined produced additively negative outcomes. In early life stage clams, however, hypoxic waters led to 30% higher mortality, while acidified waters significantly reduced growth (by 60%). Later stage clams were resistant to hypoxia or acidification separately but experienced significantly (40%) reduced growth rates when exposed to both conditions simultaneously. Collectively, these findings demonstrate that the consequences of low oxygen and acidification for early life stage bivalves, and likely other marine organisms, are more severe than would be predicted by either individual stressor and thus must be considered together when assessing how ocean animals respond to these conditions both today and under future climate change scenarios.     

鱼类对海洋升温与酸化的响应

自工业革命以来,空气中人为排放CO₂量增加,引起温室效应,导致地球表面温度升高和海水升温;同时,由于海-气界面气体交换,大气中CO₂部分溶解于海洋,引起海洋酸化。海洋升温加快鱼体内生化反应和代谢速率,并通过影响生长、觅食和繁殖等生命过程中能量供给,间接影响到鱼类种群分布、群落结构及生态系统的功能。而海水酸化会干扰海洋鱼类仔稚鱼的感觉和行为,增加其被捕食率,并削弱其野外生存能力,可能威胁自然种群补给量。综述了海洋升温、海洋酸化及其两者共同作用对海洋鱼类的影响,为预测鱼类响应全球海洋环境变化的响应趋势提供相关依据。     

Ocean Warming,More than Acidification,Reduces Shell Strength in a Commercial Shellfish Species during Food Limitation

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day⁻¹). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO₃ saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.     

End of the Century pCO2 Levels Do Not Impact Calcification in Mediterranean Cold-Water Corals

Ocean acidification caused by anthropogenic uptake of CO₂ is perceived to be a major threat to calcifying organisms. Cold-water corals were thought to be strongly affected by a decrease in ocean pH due to their abundance in deep and cold waters which, in contrast to tropical coral reef waters, will soon become corrosive to calcium carbonate. Calcification rates of two Mediterranean cold-water coral species, Lophelia pertusa and Madrepora oculata, were measured under variable partial pressure of CO₂ (pCO₂) that ranged between 380 µatm for present-day conditions and 930 µatm for the end of the century. The present study addressed both short- and long-term responses by repeatedly determining calcification rates on the same specimens over a period of 9 months. Besides studying the direct, short-term response to elevated pCO₂ levels, the study aimed to elucidate the potential for acclimation of calcification of cold-water corals to ocean acidification. Net calcification of both species was unaffected by the levels of pCO₂ investigated and revealed no short-term shock and, therefore, no long-term acclimation in calcification to changes in the carbonate chemistry. There was an effect of time during repeated experiments with increasing net calcification rates for both species, however, as this pattern was found in all treatments, there is no indication that acclimation of calcification to ocean acidification occurred. The use of controls (initial and ambient net calcification rates) indicated that this increase was not caused by acclimation in calcification response to higher pCO₂. An extrapolation of these data suggests that calcification of these two cold-water corals will not be affected by the pCO₂ level projected at the end of the century.     

Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

Ocean acidification threatens organisms that produce calcium carbonate shells by potentially generating an under‐saturated carbonate environment. Resultant reduced calcification and growth, and subsequent dissolution of exoskeletons, would raise concerns over the ability of the shell to provide protection for the marine organism under ocean acidification and increased temperatures. We examined the impact of combined ocean acidification and temperature increase on shell formation of the economically important edible mussel Mytilus edulis. Shell growth and thickness along with a shell thickness index and shape analysis were determined. The ability of M. edulis to produce a functional protective shell after 9 months of experimental culture under ocean acidification and increasing temperatures (380, 550, 750, 1000 μatm pCO ₂, and 750, 1000 μatm pCO ₂ + 2°C) was assessed. Mussel shells grown under ocean acidification conditions displayed significant reductions in shell aragonite thickness, shell thickness index, and changes to shell shape (750, 1000 μatm pCO ₂) compared to those shells grown under ambient conditions (380 μatm pCO ₂). Ocean acidification resulted in rounder, flatter mussel shells with thinner aragonite layers likely to be more vulnerable to fracture under changing environments and predation. The changes in shape presented here could present a compensatory mechanism to enhance protection against predators and changing environments under ocean acidification when mussels are unable to grow thicker shells. Here, we present the first assessment of mussel shell shape to determine implications for functional protection under ocean acidification.     

Temperature,but not pH,compromises sea urchin fertilization and early development under near-future climate change scenarios

Global warming is causing ocean warming and acidification. The distribution of Heliocidaris erythrogramma coincides with the eastern Australia climate change hot spot, where disproportionate warming makes marine biota particularly vulnerable to climate change. In keeping with near-future climate change scenarios, we determined the interactive effects of warming and acidification on fertilization and development of this echinoid. Experimental treatments (20–26°C, pH 7.6–8.2) were tested in all combinations for the ‘business-as-usual’ scenario, with 20°C/pH 8.2 being ambient. Percentage of fertilization was high (>89%) across all treatments. There was no difference in percentage of normal development in any pH treatment. In elevated temperature conditions, +4°C reduced cleavage by 40 per cent and +6°C by a further 20 per cent. Normal gastrulation fell below 4 per cent at +6°C. At 26°C, development was impaired. As the first study of interactive effects of temperature and pH on sea urchin development, we confirm the thermotolerance and pH resilience of fertilization and embryogenesis within predicted climate change scenarios, with negative effects at upper limits of ocean warming. Our findings place single stressor studies in context and emphasize the need for experiments that address ocean warming and acidification concurrently. Although ocean acidification research has focused on impaired calcification, embryos may not reach the skeletogenic stage in a warm ocean.     

Warming and Ocean Acidification Effects on Phytoplankton—From Species Shifts to Size Shifts within Species in a Mesocosm Experiment

While the isolated responses of marine phytoplankton to climate warming and to ocean acidification have been studied intensively, studies on the combined effect of both aspects of Global Change are still scarce. Therefore, we performed a mesocosm experiment with a factorial combination of temperature (9 and 15°C) and pCO₂ (means: 439 ppm and 1040 ppm) with a natural autumn plankton community from the western Baltic Sea. Temporal trajectories of total biomass and of the biomass of the most important higher taxa followed similar patterns in all treatments. When averaging over the entire time course, phytoplankton biomass decreased with warming and increased with CO₂ under warm conditions. The contribution of the two dominant higher phytoplankton taxa (diatoms and cryptophytes) and of the 4 most important species (3 diatoms, 1 cryptophyte) did not respond to the experimental treatments. Taxonomic composition of phytoplankton showed only responses at the level of subdominant and rare species. Phytoplankton cell sizes increased with CO₂ addition and decreased with warming. Both effects were stronger for larger species. Warming effects were stronger than CO₂ effects and tended to counteract each other. Phytoplankton communities without calcifying species and exposed to short-term variation of CO₂ seem to be rather resistant to ocean acidification.     

Antagonistic effects of ocean acidification and warming on hunting sharks

Ocean warming and acidification alter the physiological performance and behaviour of many small‐bodied fishes, yet the potential interactive effects of these stressors on larger predators remains poorly understood. In particular, the combined effects of elevated temperature on metabolism and of elevated CO₂ on the behaviour of large predators may not only affect their foraging behaviour, but also the communities in which their prey live. We used a factorial design to assess how projected warming and acidification create synergies or antagonisms between physiological and behavioural processes, such as swimming activity and feeding behaviour through odour tracking and vision. Temperature increased swimming activity during feeding, independent of CO₂. Although temperature also increased motivational drive to locate and accept prey, elevated CO₂ negated chemical and visual behavioural responses that enable effective hunting. Fundamental to these effects was the negligible effect of high CO₂ in isolation, but its power to negate the positive effects of temperature when brought in conjunction. The reduced potential to locate prey due to the interactive effects of ocean acidification and warming, in combination with increases in energetic demand, suggests that energetic tradeoffs will be needed for sharks to sustain themselves at an individual and population level in a future ocean.     

Signals of resilience to ocean change: high thermal tolerance of early stage Antarctic sea urchins (Sterechinus neumayeri) reared under present-day and future pCO2 and temperature

We tested the hypothesis that development of the Antarctic urchin Sterechinus neumayeri under future ocean conditions of warming and acidification would incur physiological costs, reducing the tolerance of a secondary stressor. The aim of this study is twofold: (1) quantify current austral spring temperature and pH near sea urchin habitat at Cape Evans in McMurdo Sound, Antarctica and (2) spawn S. neumayeri in the laboratory and raise early developmental stages (EDSs) under ambient (?0.7 °C; 400 µatm pCO₂) and future (+2.6 °C; 650 and 1,000 µatm pCO₂) ocean conditions and expose four EDSs (blastula, gastrula, prism, and 4-arm echinopluteus) to a one hour acute heat stress and assess survivorship. Results of field data from 2011 to 2012 show extremely stable inter-annual pH conditions ranging from 7.99 to 8.08, suggesting that future ocean acidification will drastically alter the pH-seascape for S. neumayeri. In the laboratory, S. neumayeri EDSs appear to be tolerant of temperatures and pCO₂ levels above their current habitat conditions. EDSs survived acute heat exposures >20 °C above habitat temperatures of ?1.9 °C. No pCO₂ effect was observed for EDSs reared at ?0.7 °C. When reared at +2.6 °C, small but significant pCO₂ effects were observed at the blastula and prism stage, suggesting that multiple stressors are more detrimental than single stressors. While surprisingly tolerant overall, blastulae were the most sensitive stage to ocean warming and acidification. We conclude that S. neumayeri may be unexpectedly physiologically tolerant of future ocean conditions.     

Threatened Caribbean Coral Is Able to Mitigate the Adverse Effects of Ocean Acidification on Calcification by Increasing Feeding Rate

Global climate change threatens coral growth and reef ecosystem health via ocean warming and ocean acidification (OA). Whereas the negative impacts of these stressors are increasingly well-documented, studies identifying pathways to resilience are still poorly understood. Heterotrophy has been shown to help corals experiencing decreases in growth due to either thermal or OA stress; however, the mechanism by which it mitigates these decreases remains unclear. This study tested the ability of coral heterotrophy to mitigate reductions in growth due to climate change stress in the critically endangered Caribbean coral Acropora cervicornis via changes in feeding rate and lipid content. Corals were either fed or unfed and exposed to elevated temperature (30°C), enriched pCO₂ (800 ppm), or both (30°C/800 ppm) as compared to a control (26°C/390 ppm) for 8 weeks. Feeding rate and lipid content both increased in corals experiencing OA vs. present-day conditions, and were significantly correlated. Fed corals were able to maintain ambient growth rates at both elevated temperature and elevated CO₂, while unfed corals experienced significant decreases in growth with respect to fed conspecifics. Our results show for the first time that a threatened coral species can buffer OA-reduced calcification by increasing feeding rates and lipid content.     

Differential Responses of Calcifying and Non-Calcifying Epibionts of a Brown Macroalga to Present-Day and Future Upwelling pCO2

Seaweeds are key species of the Baltic Sea benthic ecosystems. They are the substratum of numerous fouling epibionts like bryozoans and tubeworms. Several of these epibionts bear calcified structures and could be impacted by the high pCO₂ events of the late summer upwellings in the Baltic nearshores. Those events are expected to increase in strength and duration with global change and ocean acidification. If calcifying epibionts are impacted by transient acidification as driven by upwelling events, their increasing prevalence could cause a shift of the fouling communities toward fleshy species. The aim of the present study was to test the sensitivity of selected seaweed macrofoulers to transient elevation of pCO₂ in their natural microenvironment, i.e. the boundary layer covering the thallus surface of brown seaweeds. Fragments of the macroalga Fucus serratus bearing an epibiotic community composed of the calcifiers Spirorbis spirorbis (Annelida) and Electra pilosa (Bryozoa) and the non-calcifier Alcyonidium hirsutum (Bryozoa) were maintained for 30 days under three pCO₂ conditions: natural 460±59 µatm, present-day upwelling1193±166 µatm and future upwelling 3150±446 µatm. Only the highest pCO₂ caused a significant reduction of growth rates and settlement of S. spirorbis individuals. Additionally, S. spirorbis settled juveniles exhibited enhanced calcification of 40% during daylight hours compared to dark hours, possibly reflecting a day-night alternation of an acidification-modulating effect by algal photosynthesis as opposed to an acidification-enhancing effect of algal respiration. E. pilosa colonies showed significantly increased growth rates at intermediate pCO₂ (1193 µatm) but no response to higher pCO₂. No effect of acidification on A. hirsutum colonies growth rates was observed. The results suggest a remarkable resistance of the algal macro-epibionts to levels of acidification occurring at present day upwellings in the Baltic. Only extreme future upwelling conditions impacted the tubeworm S. spirorbis, but not the bryozoans.     

The reef-building coral Siderastrea siderea exhibits parabolic responses to ocean acidification and warming

Anthropogenic increases in atmospheric CO₂ over this century are predicted to cause global average surface ocean pH to decline by 0.1–0.3 pH units and sea surface temperature to increase by 1–4°C. We conducted controlled laboratory experiments to investigate the impacts of CO₂-induced ocean acidification (pCO₂ = 324, 477, 604, 2553 µatm) and warming (25, 28, 32°C) on the calcification rate of the zooxanthellate scleractinian coral Siderastrea siderea, a widespread, abundant and keystone reef-builder in the Caribbean Sea. We show that both acidification and warming cause a parabolic response in the calcification rate within this coral species. Moderate increases in pCO₂ and warming, relative to near-present-day values, enhanced coral calcification, with calcification rates declining under the highest pCO₂ and thermal conditions. Equivalent responses to acidification and warming were exhibited by colonies across reef zones and the parabolic nature of the corals'' response to these stressors was evident across all three of the experiment''s 30-day observational intervals. Furthermore, the warming projected by the Intergovernmental Panel on Climate Change for the end of the twenty-first century caused a fivefold decrease in the rate of coral calcification, while the acidification projected for the same interval had no statistically significant impact on the calcification rate—suggesting that ocean warming poses a more immediate threat than acidification for this important coral species.     

Adaptation to simultaneous warming and acidification carries a thermal tolerance cost in a marine copepod

The ocean is undergoing warming and acidification. Thermal tolerance is affected both by evolutionary adaptation and developmental plasticity. Yet, thermal tolerance in animals adapted to simultaneous warming and acidification is unknown. We experimentally evolved the ubiquitous copepod Acartia tonsa to future combined ocean warming and acidification conditions (OWA approx. 22°C, 2000 µatm CO₂) and then compared its thermal tolerance relative to ambient conditions (AM approx. 18°C, 400 µatm CO₂). The OWA and AM treatments were reciprocally transplanted after 65 generations to assess effects of developmental conditions on thermal tolerance and potential costs of adaptation. Treatments transplanted from OWA to AM conditions were assessed at the F1 and F9 generations following transplant. Adaptation to warming and acidification, paradoxically, reduces both thermal tolerance and phenotypic plasticity. These costs of adaptation to combined warming and acidification may limit future population resilience.     

Effect of ocean acidification on growth and otolith condition of juvenile scup,Stenotomus chrysops

Increasing amounts of atmospheric carbon dioxide (CO₂) from human industrial activities are causing changes in global ocean carbonate chemistry, resulting in a reduction in pH, a process termed “ocean acidification.” It is important to determine which species are sensitive to elevated levels of CO₂ because of potential impacts to ecosystems, marine resources, biodiversity, food webs, populations, and effects on economies. Previous studies with marine fish have documented that exposure to elevated levels of CO₂ caused increased growth and larger otoliths in some species. This study was conducted to determine whether the elevated partial pressure of CO₂ (pCO₂) would have an effect on growth, otolith (ear bone) condition, survival, or the skeleton of juvenile scup, Stenotomus chrysops, a species that supports both important commercial and recreational fisheries. Elevated levels of pCO₂ (1200–2600 μatm) had no statistically significant effect on growth, survival, or otolith condition after 8 weeks of rearing. Field data show that in Long Island Sound, where scup spawn, in situ levels of pCO₂ are already at levels ranging from 689 to 1828 μatm due to primary productivity, microbial activity, and anthropogenic inputs. These results demonstrate that ocean acidification is not likely to cause adverse effects on the growth and survivability of every species of marine fish. X‐ray analysis of the fish revealed a slightly higher incidence of hyperossification in the vertebrae of a few scup from the highest treatments compared to fish from the control treatments. Our results show that juvenile scup are tolerant to increases in seawater pCO_2, possibly due to conditions this species encounters in their naturally variable environment and their well‐developed pH control mechanisms.     

An Integrated Assessment Model for Helping the United States Sea Scallop (Placopecten magellanicus) Fishery Plan Ahead for Ocean Acidification and Warming

Ocean acidification, the progressive change in ocean chemistry caused by uptake of atmospheric CO₂, is likely to affect some marine resources negatively, including shellfish. The Atlantic sea scallop (Placopecten magellanicus) supports one of the most economically important single-species commercial fisheries in the United States. Careful management appears to be the most powerful short-term factor affecting scallop populations, but in the coming decades scallops will be increasingly influenced by global environmental changes such as ocean warming and ocean acidification. In this paper, we describe an integrated assessment model (IAM) that numerically simulates oceanographic, population dynamic, and socioeconomic relationships for the U.S. commercial sea scallop fishery. Our primary goal is to enrich resource management deliberations by offering both short- and long-term insight into the system and generating detailed policy-relevant information about the relative effects of ocean acidification, temperature rise, fishing pressure, and socioeconomic factors on the fishery using a simplified model system. Starting with relationships and data used now for sea scallop fishery management, the model adds socioeconomic decision making based on static economic theory and includes ocean biogeochemical change resulting from CO₂ emissions. The model skillfully reproduces scallop population dynamics, market dynamics, and seawater carbonate chemistry since 2000. It indicates sea scallop harvests could decline substantially by 2050 under RCP 8.5 CO₂ emissions and current harvest rules, assuming that ocean acidification affects P. magellanicus by decreasing recruitment and slowing growth, and that ocean warming increases growth. Future work will explore different economic and management scenarios and test how potential impacts of ocean acidification on other scallop biological parameters may influence the social-ecological system. Future empirical work on the effect of ocean acidification on sea scallops is also needed.