Query: ocean acidification

title: Ocean acidification does not impair the behaviour of coral reef fishes
abstract: The partial pressure of CO 2 in the oceans has increased rapidly over the past century, driving ocean acidification and raising concern for the stability of marine ecosystems 1 3 Coral reef fishes are predicted to be especially susceptible to end of century ocean acidification on the basis of several high profile papers 4 5 that have reported profound behavioural and sensory impairments for example, complete attraction to the chemical cues of predators under conditions of ocean acidification. Here, we comprehensively and transparently show that in contrast to previous studies end of century ocean acidification levels have negligible effects on important behaviours of coral reef fishes, such as the avoidance of chemical cues from predators, fish activity levels and behavioural lateralization (left right turning preference) Using data simulations, we additionally show that the large effect sizes and small within group variances that have been reported in several previous studies are highly improbable. Together, our findings indicate that the reported effects of ocean acidification on the behaviour of coral reef fishes are not reproducible, suggesting that behavioural perturbations will not be a major consequence for coral reef fishes in high CO 2 oceans. In contrast to previous studies, analyses now show that ocean acidification does not perturb important behaviours such as the avoidance of chemical cues from predators of coral reef fishes.

title: Coral Reefs Under Rapid Climate Change and Ocean Acidification
abstract: Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2degC by 2050 to 2100, values that significantly exceed those of at least the past 420,000 years during which most extant marine organisms evolved. Under conditions expected in the 21st century, global warming and ocean acidification will compromise carbonate accretion, with corals becoming increasingly rare on reef systems. The result will be less diverse reef communities and carbonate reef structures that fail to be maintained. Climate change also exacerbates local stresses from declining water quality and overexploitation of key species, driving reefs increasingly toward the tipping point for functional collapse. This review presents future scenarios for coral reefs that predict increasingly serious consequences for reef associated fisheries, tourism, coastal protection, and people. As the International Year of the Reef 2008 begins, scaled up management intervention and decisive action on global emissions are required if the loss of coral dominated ecosystems is to be avoided.

title: Ocean acidification impacts on coastal ecosystem services due to habitat degradation
abstract: The oceanic uptake of anthropogenic carbon dioxide emissions is changing seawater chemistry in a process known as ocean acidification. The chemistry of this rapid change in surface waters is well understood and readily detectable in oceanic observations, yet there is uncertainty about the effects of ocean acidification on society since it is difficult to scale up from laboratory and mesocosm tests. Here, we provide a synthesis of the likely effects of ocean acidification on ecosystem properties, functions and services based on observations along natural gradients in pCO2. Studies at CO2 seeps worldwide show that biogenic habitats are particularly sensitive to ocean acidification and that their degradation results in less coastal protection and less habitat provisioning for fisheries. The risks to marine goods and services amplify with increasing acidification causing shifts to macroalgal dominance, habitat degradation and a loss of biodiversity at seep sites in the tropics, the sub tropics and on temperate coasts. Based on this empirical evidence, we expect ocean acidification to have serious consequences for the millions of people who are dependent on coastal protection, fisheries and aquaculture. If humanity is able to make cuts in fossil fuel emissions, this will reduce costs to society and avoid the changes in coastal ecosystems seen in areas with projected pCO2 levels. A binding international agreement for the oceans should build on the United Nations Sustainable Development Goal to 'minimise and address the impacts of ocean acidification'

title: Effects of Ocean Acidification on Marine Photosynthetic Organisms Under the Concurrent Influences of Warming, UV Radiation, and Deoxygenation
abstract: The oceans take up over 1 million tons of anthropogenic CO2 per hour, increasing dissolved pCO2 and decreasing seawater pH in a process called ocean acidification. At the same time greenhouse warming of the surface ocean results in enhanced stratification and shoaling of upper mixed layers, exposing photosynthetic organisms dwelling here to increased visible and UV radiation as well as to a decreased nutrient supply. In addition, ocean warming and anthropogenic eutrophication reduce the concentration of dissolved O2 in seawater, contributing to the spread of hypoxic zones. All of these global changes interact to affect marine primary producers. Such interactions have been documented, but to a much smaller extent compared to the responses to each single driver. The combined effects could be synergistic, neutral or antagonistic depending on species or the physiological processes involved as well as experimental setups. For most calcifying algae, the combined impacts of acidification, solar UV and/or elevated temperature clearly reduce their calcification; for diatoms, elevated CO2 and light levels interact to enhance their growth at low, but inhibit it at high levels of sunlight. For most photosynthetic nitrogen fixers (diazotrophs) acidification associated with elevated CO2 may enhance their N2 fixation activity, but interactions with other environmental variables such as trace metal availability may neutralize or even reverse these effects. Macroalgae, on the other hand, either as juveniles or adults, appear to benefit from elevated CO2 with enhanced growth rates and tolerance to lowered pH. There has been little documentation of deoxygenation effects on primary producers, though theoretically elevated CO2 and decreased O2 concentrations could selectively enhance carboxylation over oxygenation catalyzed by Rubisco and thereby benefit autotrophs. Overall, most ocean global change biology studies have used single and/or double stressors in laboratory tests. This overview examines the combined effects of ocean acidification with other features such as warming, solar UV radiation and deoxygenation, focussing on primary producers.

title: Experimental assessments of marine species sensitivities to ocean acidification and co stressors: how far have we come?
abstract: Experimental studies assessing the potential impacts of ocean acidification on marine organisms have rapidly expanded and produced a wealth of empirical data over the past decade. This perspective examines four key areas of transformative developments in experimental approaches: (1) methodological advances; (2) advances in elucidating physiological and molecular mechanisms behind observed CO2effects; (3) recognition of short term CO2variability as a likely modifier of species sensitivities (Ocean Variability Hypothesis) and (4) consensus on the multistressor nature of marine climate change where effect interactions are still challenging to anticipate. No single experiment allows predicting the fate of future populations. But sustaining the accumulation of empirical evidence is critical for more robust estimates of species reaction norms and thus for enabling better modeling approaches. Moreover, advanced experimental approaches are needed to address knowledge gaps including changes in species interactions and intraspecific variability in sensitivity and its importance for the adaptation potential of marine organisms to a high CO2world.

title: (Re)Framing ocean acidification in the context of the United Nations Framework Convention on Climate Change (UNFCCC) and Paris Agreement
abstract: Ocean acidification is most frequently framed by the scientific community as a concurrent threat to climate change, rather than an effect of it. This separation of the two phenomena has long been deemed as a way of garnering heightened policy attention for ocean acidification rather than having it bound up in the often contested politics of climate change. This effort, however, appears to have resulted in the inadvertent placing of ocean acidification outside of the mandate of the United Nations Framework Convention on Climate Change (UNFCCC) This has created a significant gap in the global governance of this issue with no multilateral agreement understood as having jurisdiction over the mitigation of rising ocean acidity. For these reasons this paper argues that an alternative framing of ocean acidification as an effect of climate change is warranted. This would include ocean acidification in the core obligations of the Convention, thereby filling the mitigation governance gap and avoiding perverse implementation outcomes. It is contended that interpreting the UNFCCC in this way is more consistent with its objective and purpose than the existing interpretations that place ocean acidification beyond the remit of the Convention. Key policy insights Ocean acidification is best understood as an effect of climate change in the context of the UNFCCC, and therefore is included in its obligations to combat climate change and its adverse effects. An obligation to address ocean acidification has implications for the way that the provisions of the Convention, particularly on mitigation, are implemented. Mitigation activities that exacerbate ocean acidification or lead to emission reduction pathways that do not prevent dangerous acidification should be deemed inconsistent with the Convention. Protection, conservation and restoration of coastal and marine ecosystems should become a priority area for action within the UNFCCC.

title: Ocean acidification refugia in variable environments
abstract: Climate change refugia in the terrestrial biosphere are areas where species are protected from global environmental change and arise from natural heterogeneity in landscapes and climate. Within the marine realm, ocean acidification, or the global decline in seawater pH, remains a pervasive threat to organisms and ecosystems. Natural variability in seawater carbon dioxide (CO2) chemistry, however, presents an opportunity to identify ocean acidification refugia (OAR) for marine species. Here, we review the literature to examine the impacts of variable CO2 chemistry on biological responses to ocean acidification and develop a framework of definitions and criteria that connects current OAR research to management goals. Under the concept of managing vulnerability, the most likely mechanisms by which OAR can mitigate ocean acidification impacts are by reducing exposure to harmful conditions or enhancing adaptive capacity. While local management options, such as OAR, show some promise, they present unique challenges, and reducing global anthropogenic CO2 emissions must remain a priority.

title: Anthropogenic ocean acidification over the twenty first century and its impact on calcifying organisms
abstract: Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms such as corals and some plankton will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean carbon cycle to assess calcium carbonate saturation under the IS92a 'business as usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high latitude ecosystems could develop within decades, not centuries as suggested previously.

title: Coral physiology and microbiome dynamics under combined warming and ocean acidification
abstract: Rising seawater temperature and ocean acidification threaten the survival of coral reefs. The relationship between coral physiology and its microbiome may reveal why some corals are more resilient to these global change conditions. Here, we conducted the first experiment to simultaneously investigate changes in the coral microbiome and coral physiology in response to the dual stress of elevated seawater temperature and ocean acidification expected by the end of this century. Two species of corals, Acropora millepora containing the thermally sensitive endosymbiont C21a and Turbinaria reniformis containing the thermally tolerant endosymbiont Symbiodinium trenchi, were exposed to control (26.5degC and pCO2 of 364 matm) and treatment (29.0degC and pCO2 of 750 matm) conditions for 24 days, after which we measured the microbial community composition. These microbial findings were interpreted within the context of previously published physiological measurements from the exact same corals in this study (calcification, organic carbon flux, ratio of photosynthesis to respiration, photosystem II maximal efficiency, total lipids, soluble animal protein, soluble animal carbohydrates, soluble algal protein, soluble algal carbohydrate, biomass, endosymbiotic algal density, and chlorophyll a) Overall, dually stressed A. millepora had reduced microbial diversity, experienced large changes in microbial community composition, and experienced dramatic physiological declines in calcification, photosystem II maximal efficiency, and algal carbohydrates. In contrast, the dually stressed coral T. reniformis experienced a stable and more diverse microbiome community with minimal physiological decline, coupled with very high total energy reserves and particulate organic carbon release rates. Thus, the microbiome changed and microbial diversity decreased in the physiologically sensitive coral with the thermally sensitive endosymbiotic algae but not in the physiologically tolerant coral with the thermally tolerant endosymbiont. Our results confirm recent findings that temperature stress tolerant corals have a more stable microbiome, and demonstrate for the first time that this is also the case under the dual stresses of ocean warming and acidification. We propose that coral with a stable microbiome are also more physiologically resilient and thus more likely to persist in the future, and shape the coral species diversity of future reef ecosystems.

title: Ocean acidification affects coral growth by reducing skeletal density
abstract: Ocean acidification (OA) threatens coral reef futures by reducing the concentration of carbonate ions that corals need to construct their skeletons. However, quantitative predictions of reef futures under OA are confounded by mixed responses of corals to OA in experiments and field observations. We modeled the skeletal growth of a dominant reef building coral, Porites, as a function of seawater chemistry and validated the model against observational data. We show that OA directly and negatively affects one component of the two step growth process (density) but not the other (linear extension) Combining our growth model with Global Climate Model output, we show that skeletal density of Porites corals could decline by up to 20.3% over the 21st century solely due to OA. Ocean acidification (OA) is considered an important threat to coral reef ecosystems, because it reduces the availability of carbonate ions that reef building corals need to produce their skeletons. However, while theory predicts that coral calcification rates decline as carbonate ion concentrations decrease, this prediction is not consistently borne out in laboratory manipulation experiments or in studies of corals inhabiting naturally low pH reefs today. The skeletal growth of corals consists of two distinct processes: extension (upward growth) and densification (lateral thickening) Here, we show that skeletal density is directly sensitive to changes in seawater carbonate ion concentration and thus, to OA, whereas extension is not. We present a numerical model of Porites skeletal growth that links skeletal density with the external seawater environment via its influence on the chemistry of coral calcifying fluid. We validate the model using existing coral skeletal datasets from six Porites species collected across five reef sites and use this framework to project the impact of 21st century OA on Porites skeletal density across the global tropics. Our model predicts that OA alone will drive up to 20.3 5.4% decline in the skeletal density of reef building Porites corals.