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Erica Evans EV128 Ocean Acidification and the impacts for Northeast Pacific fisheries in relation to the California Current System Introduction Our climate has been changing more rapidly in the past 200 years than it ever has during our presence as a species on earth (Karl & Trenberth 2003,1720). Humans, through the burning of fossil fuels and greenhouse gas emissions, have been the main driver of climate since the beginning of the industrial revolution (Karl & Trenberth 2003, 1720). Burning of fossil fuels has increased greenhouse gas emissions by more than a third when contrasted with pre-industrial levels (Barnosky et al 2012, 54). This increase is linked to rising temperatures, changing ocean chemistries, and shifts in terrestrial and marine ecosystems (Barnosky et al 2012, 56-57; Ainsworth et al 2011, 1217). Changes in ocean chemistry can have profound ecological and economic impacts. Oceans are one of the most important regulators in the earth’s biogeochemical cycle, and provide habitat for an enormous number and diversity of species. Ocean acidification is caused by the uptake of CO2 into marine ecosystems, and contributes to the impacts of climate change by decreasing pH and changing carbonate saturation levels (Zeebe 2012, 141-143; Logan 2012, 820-821). Changing pH and carbonate saturation levels contributes to the degradation of populations of calcifying organisms, and declines in many fisheries (Ainsworth et al 2011; Orr et al 2005). This paper will focus on the impacts of ocean acidification on fisheries in the Northeast Pacific, centering on the degradation of both fish and oyster hatcheries in relation to changes in the California Current System (CCS). This paper will also discuss recommendation for future research into the physiological effects of ocean acidification on fished populations. 1 Chemistry Oceans are the largest sinks of inorganic carbon in the carbon cycle. From 1750 to 2000 the oceans absorbed approximately one third of anthropogenic atmospheric carbon (Baird et al 2009, 460, Logan 2010, 819). CO2 concentration in the atmosphere has increased by ~40% since the beginning of the industrial era (Zeebe, 2012, 142). The absorption of carbon into the ocean system has resulted in a net decrease in oceanic pH. Since the late 18th century, mean surface ocean pH has dropped from 8.2 to 8.1, a change roughly equivalent to a 30% increase in hydrogen ions (Logan 2010, 819). The pH levels have not dropped below 8.1 during the past two million years (Raven et al 2005, 1; Calderia 2003, 365). If current trends continue we can expect to see pH drop by another 0.3-0.4. This drop would be roughly equivalent to a 150% increase in hydrogen ions (Logan 2010, 819). Oceans act as a buffer for CO2 in the atmosphere by absorbing CO2 and converting it into carbonic acid (H2CO3), which breaks down into bicarbonate (HCO3-), carbonate (CO32-) and hydrogen ions (Logan 2010, 819). These reactions can be reversed, to help prevent large-scale changes in salinity. The reversal of these reactions is dependent on ion concentrations, temperature, salinity and pressure. This directionally means that as oceanic chemistry adjusts to accommodate for excess atmospheric carbon, it decreases in ability to buffer and regulate oceanic acidity. When atmospheric CO2 is high, fewer carbonate ions are produced and the ocean has a lower pH (Logan 2010, 819). Figure 1 demonstrates the relationship between changes in alkalinity, photosynthesis, calcite formation and CO2 release. Carbonate is essential for the formation and development of many organisms in the oceans. We have seen a 10% decrease in carbonate concentration in the oceans since preindustrial times, with a predicted decrease of 50% by 2100 (Baird et al 2009, 460-461). 2 Decrease in carbonate concentration will have profound impacts across oceanic environments. Calcifying organisms play a central role in oceanic ecosystems, and a decrease in their populations will have compounding effects up the food chain (Baird et al 2009, 462). Fig. 1 Figure shows the effects of various processes on ocean alkalinity and dissolved inorganic carbon. Total dissolved inorganic carbon (TDOC) is changed exclusively by invasion and release of CO2, while photosynthesis and respiration change total alkalinity (TA). CaCO3 formation and dissolution affects both TDOC and TA. Source: Zeebe (2012, 145) Consequences for calcification rates and fisheries Impacts of acidification on Northeast Pacific fisheries Acidification affects fisheries containing salmon, tuna and herring through population and diversity losses lower down in the food chain, along with physiological changes (Belli 2012, 25; Gosling et al 2011, 447). These fish, along with marine birds, some whales, and seals depend on pteropods as a major source of food. Ocean acidification limits the ability of pteropods to form their shells by decreasing the availability of carbonate minerals (Belli 2012, 25). Simulations from five Ecopath with Ecosim models, presented at the International Symposium on Climate Change by Ainsworth et al, were used to analyze responses of the food web in Northeast Pacific marine environments. These simulations considered five different 3 climate models and assessed the impacts of biomass change, un-fished functional groups, ecosystem characteristics, and the state of the ecosystem in the 50th year of the simulation (Ainsworth et al 2011, 1217). Ecopath with Ecosim modeling (EWE) is a model system that combines the living and non-living aspects of an ecosystem. This modeling approach incorporates thermodynamic accounting to track the flow of energy throughout an ecosystem. The Ecopath model is the initialization state for the Ecosim model, and represents a static point in time. The Ecosim model uses two primary equations (fig. 2) to account for primary producers and consumers. In these equations B𝑖 is the biomass of the prey and B𝑗 is the biomass of the predator. The parameters are then used relate the production rate (P), ecotrophic efficiency (EE), the emigration of species in and out of the ecosystem (E), the growth efficiency (g), the immigration rate (I), natural and fishing mortality (M) and (F) and the number of functional groups (n) (Ainsworth et al 2011, 1218). Fig. 2 Equation 1 accounts for primary producers, equation 2 for consumers. f() is the functional relationship used to predict consumption rates. Source: Ainsworth et al 2011, 1218 Factoring in primary production changes, zooplankton size, dissolved oxygen, ocean acidification effects, and range shifts, coupled with all the climate effects together “reduces landings by 77% under the moderate climate effect strength scenario and by as much as 85% under the severe climate effect strength scenario” (Ainsworth et al 2011, 1223). This modeling 4 simulation showed that shifts in range are the dominant effect of climate change as a factor in decreasing fish populations. These modeling simulations, while fairly general, can give us insight into the future of fisheries in the Northeast Pacific region. We can predict that 1) some fisheries and species will increase while others will decline, 2) fisheries and species will not respond uniformly over all areas, 3) interactions between the variable effects of climate change in different regions will result in a greater variety of changes in fisheries when compared to one effect alone (Fig 3). While some species may experience positive growth, we can hypothesize that fisheries generally suffer as a result of climate change. Fished species tend to experience greater losses than unfished species (Ainsworth et al 2011, 1226). Fig 3 Averaged values across all EWE models showing projected fish landings for biomass and projected fish landings for the year 2060. Baseline numbers represent landings and biomass numbers without climate change. Error bars represent the range of values predicted using moderate, conservative and substantial effect sizes. Source: Ainsworth et al 2011, 1222 5 Studies have also shown links between physiological changes in fish populations and ocean acidification. There are connections between ocean acidification and impaired inner ear development (Checkley et al 2009, 1683), sensitivity to predation (Munday et al 2010, 1850), and alterations in olfactory sensing (Munday et al 2009, 1-3). There is also evidence that acidification leads to decreased cellular activity and respiratory function. These decreases can lead to increased mortality in fish populations (Raven et al 2005, 19). These changes could have profound impacts by altering ranges and habitat niches across fish populations. It is difficult to predict what will happen economically to affected fisheries, as we can only view economic balance within our current economic framework. Such frameworks are highly limited when applied over centuries or decades. It is also possible that losses in production will be offset by increases in price of the commodity, as decreasing production levels on a global scale will drive up prices in all markets. When assessed within the context of rapid shifts in consumer tastes and interests, it is likely that markets will adjust to variations in production levels (Quesne et al 2011, 340). Fisheries can also be managed to avoid the effects of climate forcing on fished populations. The sensitivity of fished populations can increase with exploitation, indicating that more informed management practices could reduce the risk of largescale impacts (Perry et al 2010, 19). Impacts of ocean acidification on calcifying organisms and Northeast Pacific oyster hatcheries Ocean acidification affects oysters and other marine-calcifying organisms. Ocean circulation patterns, especially along the west coast of the United States make these areas particularly susceptible (Belli 2012, 24). The upwelling of cold bottom currents into shallower shore areas brings acidified chemistry, along with reduced saturation of carbonate (McPhaden 6 2006, 1740). This water can have a pH as low as ~7.5, in contrast to usual pH levels ~8.2. This cold acidic water is pulled into hatcheries where it inhibits the growth of calcifying organisms. The ability of oysters and other shellfish, lobsters, clams as well as planktons and corals to build their shells is related to saturation levels (Belli 2012, 25). Saturation is the amount of carbonate mineral dissolved in a body of water. Saturation is not evenly distributed throughout oceanic systems and is inversely related to the solubility of a carbonate mineral. The coefficient of saturation is dependent on pressure, temperature and salinity (Logan 2010, 820). The inverse relationship between solubility and saturation state results in high saturation in warm shallow tropical waters and low saturation in colder deep water. This reduction in carbonate minerals reduces the ability of many marine organisms to develop properly (Service 2012, 147). When saturation levels equal 1, there is an equally likely chance of dissolution as there is of carbonate formation. The saturation horizon is the plane in the ocean below which saturation is less than 1 and above which saturation is greater than 1 (Logan 2010, 821). As oceans become more acidified, the saturation horizon moves upward, making it increasingly difficult for carbonate-dependent organisms to develop (Logan 2010, 821). Laboratory experiments show a strong decrease in calcifying rates as pH decreases (Raven et al 2005, 20). Solutions are available on a local level, but function only as a piecemeal solution. Shellfish farmers can monitor acidity and wind velocity to limit letting acidic water into hatcheries, as well as filling tanks in the afternoon when waters have warmed (Service 2012, 147). The 2012 U. S. federal budget cut funds from several monitoring projects off the Washington coast, reducing the effectiveness of these operations. It is also important to note that these mitigating actions become increasingly less effective as ocean chemistry becomes more 7 uniformly acidic, and more and more of the water column becomes under saturated (Belli 2012, 24). The California Current System Modeling focusing on the California Current System (CCS) shows that following recent trends, we will see rapid increases in under saturated waters in the top 60 meters of ocean. By 2050, California Current System waters will be under saturated during 50% of the year (Service 2012, 148; Gruber et al 2012, 220). Figure 4 shows projections for mean saturation rates extending to the year 2064. These under-saturated conditions will pose extreme difficulties for larval organisms developing at or near the surface. Approximately 73% of profits from the $3.8 billion a year US commercial fishing industry comes directly from calcifying organisms and their predators (Denman 2011, 1019). While most US fisheries will be impacted by acidification in some way, CCS upwelling will likely exacerbate this detrimental change in the Northeast Pacific. Fig 4. Mean Saturation rates of calcite (right y-axis) and aragonite (left y-axis) in the near shore regions of the California Current System (CCS), in relation to atmospheric CO2. Included are the mean evolutions of the Tropical, Arctic and Southern Oceans. Source: Gruber et al 2012, 222 8 Mitigation Even if anthropogenic CO2 levels were reduced to zero within the next few days, ocean pH levels would continue to decrease for the next several decades. The under-saturated water washing up along the coasts has been circulating for 30-60 years, and was therefore exposed to CO2 levels at levels much lower than today. This indicates that waters exposed to higher levels of CO2 are still circulating, and have yet to make their way into global current systems (Service 2012, 148). Geoengineering has been suggested as a means to limit climate change and the resultant impacts. Directly addressing ocean acidification would involve depositing 13 billion tons of limestone into the world’s oceans annually, and is therefore not a feasible approach to mitigating the acidification process (Logan 2009, 462). However geoengineering projects to limit or remove CO2 are marginally more feasible and could affect ocean acidification indirectly. These proposals center on climate engineering, or creating uniform reductions in incoming shortwave radiation. These proposals involve injecting high volumes of aerosols into the atmosphere to create large scale cooling effects. While this would not directly solve acidification, it could scale back the effects by redistributing emissions and CO2 concentrations across land, oceanic and atmospheric environments (Mathews et al 2009, 1,4). The effects of acidification can be mitigated through the restoration of costal sea grass areas. Sea grass stores CO2 in its roots, which helps to ameliorate the impacts of acidification. Similarly, repairing mangroves, salt marshes and other coastal wetland areas can have a positive effect on reducing ocean acidity (Belli 2012, 31). However, this will not be enough to remove the entirety of the impact. Without regulation on atmospheric carbon, there will not be a substantial decrease in acidification rate. Recommendations have been made to limit atmospheric 9 CO2 at 550 ppm because at levels above 550ppm aragonite becomes highly under saturated. However 550ppm is probably too high to avoid other detrimental effects to marine ecosystems. It is therefore recommended that atmospheric levels should be kept below 500ppm at the very least, and below 450ppm following the precautionary principle (Turley et al 2010, 791). Discussion and recommendations for future research While most of the research referenced in this article is fairly conclusive, there remains some debate about the ability of fished populations to adjust, the consequences for fished populations vs. non-fished populations, as well as the physiological impacts of acidification on fish. Ainsworth et al (2011) indicates that fished populations will be worse off in global climate change scenarios than non-fished populations, and that fishing acts as a stressor to execrable the impacts of climate change. Quesne et al. (2011) found no discernable difference between fished and non-fished populations in climate change scenarios. More research should be undertaken into this area to discern if fishing acts as an external stressor. There is also debate about the ability of populations to adjust to changes in range, diets and acidification. Many species (particularly those dependent on calcifying processes) will experience decreases in population (Orr et al 2005, 681, 685). However, many marine organisms exist within flexible food webs, and can adjust diets and ranges in response to resource scarcity. Studies in North Sea populations show species transitioning to drastically different diets in response to environmental stresses (Quesne et al 2011, 336). It is unclear if other populations will be able to make similar adjustments, particularly in fishery dependent areas. Fished populations will not necessarily decrease uniformly. Increases in CO2 levels could facilitate phytoplankton growth, thereby encouraging the growth of fish populations further up 10 the food chain. Any alteration to primary producers will have effects further up in the food web (Quesne et al 2001, 337). However, analysis predicts that the trend for fished populations will be generally negative (Ainsworth et al 1223). Checkley et al (2009), Munday et al (2009), Munday et al (2009), and Quesne et al (2011) indicate that decreasing pH can affect physiological functions of fish populations. While the links between impaired inner ear development, olfactory capacity and ability to sense predators are fairly understood, the extent of these links in the larger scale of populations is still unknown. Further research should be undertaken to help understand the ramifications of ocean acidification on a large scale. While impacts are beginning to become evident in oyster hatcheries, (Belli 2012, 24-25), we still do not fully understand what global changes will happen to fish populations as our oceans become increasingly acidified. Conclusion Current literature displays the direct links between ocean acidification and detrimental effects to fisheries and calcifying organisms. As the earth continues to warm, we will see pH decreases far from what we have experienced as a species. It is important for the scientific and political communities to be aware of the ramifications of climate change in the context of ocean acidification (Baird et al, 2009). Acidification-created change in ecosystems will affect fisheries and other ocean resources, leading to global economic impacts. It is increasingly clear that an international consensus is needed on how to directly mitigate runaway CO2 increases, as well as providing strategies for adaptation. While there is general consensus in the scientific community, there has not been a policy consensus, or 11 movement towards implementation of law to reduce or mitigate the impacts of oceanic acidification (Baird et al 2009, 462-464). The United States’ market could shift away from dependence on fisheries, however many undeveloped countries rely on fishing as a primary source of protein and income (Wittig 2012). The interdependence of the world’s oceanic ecosystems makes an international solution exceedingly important. We need to be able to reassess in a global context what comes next and how to avoid the consequences of acidification. It is clear that without some form of international regulation, we will continue to see the impacts of anthropogenic climate change and oceanic acidification perpetuate into the future. 12 References Ainsworth, C. H., Samhouri, J. F., Busch, D. S., Cheung, W. W. L., Dunne, J., & Okey, T. A. (2011). Potential impacts of climate change on northeast pacific marine food webs and fisheries. ICES Journal of Marine Science, 68(6), 1217-1228. Baird, R., Simons, M., & Stephens, T. (2009). Ocean acidification: A litmus test for international law. Carbon & Climate Law Review, 3, 459-471. 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