FK9T15 Dead fish Lagoa Rodrigo de Freitas. Image shot 03/2013. Exact date unknown.

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1. THIS POST IS A CRITICAL REVIEW OF Licker, R., et al. “Attributing ocean acidification to major carbon producers.” Environmental Research Letters 14.12 (2019): 124060: ABSTRACT: Recent research has quantified the contributions of CO₂ and CH₄ emissions traced to the products of major fossil fuel companies and cement manufacturers to global atmospheric CO₂, surface temperature, and sea level rise. This work has informed societal considerations of the climate responsibilities of these major industrial carbon producers. Here, we extend this work to historical (1880–2015) and recent (1965–2015) acidification of the world’s ocean. Using an energy balance carbon-cycle model, we find that emissions traced to the 88 largest industrial carbon producers from 1880–2015 and 1965–2015 have contributed ~55% and ~51%, respectively, of the historical 1880–2015 decline in surface ocean pH. As ocean acidification is not spatially uniform, we employ a three-dimensional ocean model and identify five marine regions with large declines in surface water pH and aragonite saturation state over similar historical (average 1850–1859 to average 2000–2009) and recent (average 1960–1969 to average of 2000–2009) time periods. We characterize the biological and socioeconomic systems in these regions facing loss and damage from ocean acidification in the context of climate change and other stressors. Such analysis can inform societal consideration of carbon producer responsibility for current and near-term risks of further loss and damage to human communities dependent on marine ecosystems and fisheries vulnerable to ocean acidification.
2. The full text of the paper is available in PDF format online [LINK] . A media story about the paper has been published by Science Alert  magazine with full text also available online [LINK] .
3. The Environmental Research Letters paper and the Science Alert article along with tweets on Twitter by one of the authors of the paper have raised an alarm about the observed trend in ocean acidification. Specifically, the paper stresses and highlights the human cause of ocean acidification in terms of CO2 emissions of the industrial economy by identifying industrial enterprises that are responsible for significant portions of the emissions. This aspect of fossil fuel emissions is found to be harmful to the environment. The harm by anthropogenic ocean acidification is identified in terms of destruction of marine life as well as a degradation of marine ecosystem in terms of its ability to nurture ocean life as we know it. It is further claimed that climate action in the form of reducing emissions according to UNFCCC sponsored international agreements is urgently needed to attenuate the ocean acidification horror caused by the fossil fuel emissions of the industrial economy.
4. In a related post [LINK] ocean acidification data from 1958 to 2014 are presented as shown in the chart below. The data show a rising trend in ocean acidification by carbon dioxide during a period of rising emissions.
5. 
6. The causation hypothesis of ocean acidification identifies fossil fuel emissions as the obvious source of CO2 as an extension of AGW climate change theory that identifies CO2 in fossil fuel emissions as the agent of change that is driving the observed rise in atmospheric CO2 concentration and surface temperature. This assumed causation hypothesis is thought to be supported by the data by virtue of the observation that both the acidification and the emission time series are rising together. Although causation is likely in such circumstances, that the two time series are rising at the same time does not in itself prove causation.
7. In a related post [LINK] the causation hypothesis is tested with mass balance and detrended correlation analysis. The mass balance test checks to ensure that the the rate of CO2 absorption by the ocean and the rate of CO2 production in fossil fuel emissions are consistent with causation. The results of the mass balance test appear in the table below. They show that even in the unlikely event that all of the CO2 in fossil fuel emissions dissolved into the ocean it would be unable to create annual changes in oceanic CO2 seen in the data.
8. Therefore, the real cause of these changes must lie in the ocean itself. These mass balance relationships are not consistent with the atmospheric causation hypothesis for the observed changes in ocean acidification. The analysis suggests an oceanic geological cause as in the PETM [LINK] .
9. A further test of the atmospheric causation of ocean acidification is carried out with detrended correlation analysis. The results appear in the chart below. No correlation between emissions and ocean acidification is found. The results do not support the usual assumption that fossil fuel emissions cause ocean acidification.
10. An additional consideration is the observed vertical gradient in ocean acidification. The data show [LINK] that the acidification intensifies with depth. This gradient does not support the atmospheric source hypothesis. Rather, it suggests an oceanic source of CO2 in the ocean acidification trend that appears to have become a priority of climate science to be described as an impact of fossil fuel emissions. 
11. CONCLUSION: The analyses presented above and in a related post [LINK] do not support the assumed atmospheric causation of ocean acidification by way of fossil fuel emissions. That climate science is fixated on such causation provides further evidence, discussed in related posts, that the science of climate science contains an extreme form of atmosphere bias and a pre-determined causation sequence that begins with fossil fuel emissions [LINK] , [LINK] , [LINK] . Unbiased and objective scientific inquiry should and would include the role of submarine geological activity in the investigation of ocean acidification given the data. It is noted that the most salient example of ocean acidification in the paleo record is the PETM (Paleocene Eocene Thermal Maximum) event that involved catastrophic ocean acidification by the ocean itself. This event is described in a related post [LINK] .

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POSTSCRIPT

PETER WADHAMS EXPLAINS THE HORRORS OF OCEAN ACIDIFICATION [LINK]

SUMMARY

1. “CO2 in fossil fuel emissions enter an alkaline ocean and make it acidic” {The extreme atmosphere bias of atmospheric scientists on display here. As to the ocean becoming “acidic”, it ain’t so. Acidification does reduce the pH of the alkaline ocean but not all the way down to below pH<7 to make it acidic . The ocean still remains alkaline but at a lower pH. Not even in the horrific acidification of the PETM did the ocean pH go below 7 into being acidic}
2. “Shellfish capture and remove carbon dioxide into the shell and when they die they take the CO2 to the grave with them but AGW fossil fueled ocean acidification is making the ocean acidic and re-dissolving the shell to release CO2 from it and to return the CO2 back to the atmosphere. The CO2 that was removed from the atmosphere by the ocean and the CO2 that had been trapped in shells are thus returned to the atmosphere as a feedback to the climate system and to ocean acidification.” {How far the termites have spread and how long and how well they have dined! A Biblical form of climate fear mongering is on display here. Millions of years of CO2 trapped in shells returned to the atmosphere for the ultimate CO2 hell that will end it all! And all of this triggered by fossil fuel emissions! Although strangely this CO2 bomb was not triggered by the PETM.}
3. If shellfish of the deep are threatened by carbon dioxide in our fossil fuel emissions, we need an explanation for why the shellfish of the deep like to hang out near hydrothermal vents.
   

   
4. Below is a brief Ocean Acidification Bibliography that explores these projected  impacts of ocean acidification on ocean life forms. The results are less dramatic than that painted by Wadhams. Of note is Nagelkerken (2016) and similar papers that chose to study ocean acidification in the vicinity of hydrothermal vents. Thus, though natural sub-marine flows of carbon dioxide is recognized in empirical research it is  completely ignored in climate change theory which relies entirely on atmospheric phenomena to explain changes in the ocean. As a footnote, the total mass of the atmosphere and ocean taken together is 1.32E18 tonnes of which the ocean is 99.61% and the atmosphere 0.39%. In the science of climate science, oceanic sources of carbon are ignored. The atmosphere tail wags the ocean dog.
5. A survey of oceanic sources of carbon emissions is presented in a related post [LINK] .

RED LINES MARK LOCATION OF KNOWN HYDROTHERMAL VENTS

OCEAN ACIDIFICATION BIBLIOGRAPHY

1. 2005: Orr, James C., et al. “Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms.” Nature 437.7059 (2005): 681. 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.
2. 2007: Hoegh-Guldberg, Ove, et al. “Coral reefs under rapid climate change and ocean acidification.” science 318.5857 (2007): 1737-1742. Atmospheric carbon dioxide concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C 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.
3. 2008: Anthony, Kenneth RN, et al. “Ocean acidification causes bleaching and productivity loss in coral reef builders.” Proceedings of the National Academy of Sciences (2008). Ocean acidification represents a key threat to coral reefs by reducing the calcification rate of framework builders. In addition, acidification is likely to affect the relationship between corals and their symbiotic dinoflagellates and the productivity of this association. However, little is known about how acidification impacts on the physiology of reef builders and how acidification interacts with warming. Here, we report on an 8-week study that compared bleaching, productivity, and calcification responses of crustose coralline algae (CCA) and branching (Acropora) and massive (Porites) coral species in response to acidification and warming. Using a 30-tank experimental system, we manipulated CO₂ levels to simulate doubling and three- to fourfold increases [Intergovernmental Panel on Climate Change (IPCC) projection categories IV and VI] relative to present-day levels under cool and warm scenarios. Results indicated that high CO₂ is a bleaching agent for corals and CCA under high irradiance, acting synergistically with warming to lower thermal bleaching thresholds. We propose that CO₂ induces bleaching via its impact on photoprotective mechanisms of the photosystems. Overall, acidification impacted more strongly on bleaching and productivity than on calcification. Interestingly, the intermediate, warm CO₂ scenario led to a 30% increase in productivity in Acropora, whereas high CO₂ lead to zero productivity in both corals. CCA were most sensitive to acidification, with high CO₂ leading to negative productivity and high rates of net dissolution. Our findings suggest that sensitive reef-building species such as CCA may be pushed beyond their thresholds for growth and survival within the next few decades whereas corals will show delayed and mixed responses.
4. 2008: Fabry, Victoria J., et al. “Impacts of ocean acidification on marine fauna and ecosystem processes.” ICES Journal of Marine Science 65.3 (2008): 414-432. Oceanic uptake of anthropogenic carbon dioxide (CO₂) is altering the seawater chemistry of the world’s oceans with consequences for marine biota. Elevated partial pressure of CO₂ (pCO₂) is causing the calcium carbonate saturation horizon to shoal in many regions, particularly in high latitudes and regions that intersect with pronounced hypoxic zones. The ability of marine animals, most importantly pteropod molluscs, foraminifera, and some benthic invertebrates, to produce calcareous skeletal structures is directly affected by seawater CO₂ chemistry. CO₂influences the physiology of marine organisms as well through acid-base imbalance and reduced oxygen transport capacity. The few studies at relevant pCO₂ levels impede our ability to predict future impacts on foodweb dynamics and other ecosystem processes. Here we present new observations, review available data, and identify priorities for future research, based on regions, ecosystems, taxa, and physiological processes believed to be most vulnerable to ocean acidification. We conclude that ocean acidification and the synergistic impacts of other anthropogenic stressors provide great potential for widespread changes to marine ecosystems.
5. 2009: Miller, A. Whitman, et al. “Shellfish face uncertain future in high CO2 world: influence of acidification on oyster larvae calcification and growth in estuaries.” Plos one 4.5 (2009): e5661. Human activities have increased atmospheric concentrations of carbon dioxide by 36% during the past 200 years. One third of all anthropogenic CO₂ has been absorbed by the oceans, reducing pH by about 0.1 of a unit and significantly altering their carbonate chemistry. There is widespread concern that these changes are altering marine habitats severely, but little or no attention has been given to the biota of estuarine and coastal settings, ecosystems that are less pH buffered because of naturally reduced alkalinity.
6. 2009: Doney, Scott C., et al. “Ocean acidification: the other CO2 problem.” Annual Review of Marine Science (2009). Rising atmospheric carbon dioxide (CO₂), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO₂ emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO₂ conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO₂ and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions.
7. 2010: Talmage, Stephanie C., and Christopher J. Gobler. “Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish.” Proceedings of the National Academy of Sciences 107.40 (2010): 17246-17251. The combustion of fossil fuels has enriched levels of CO₂ in the world’s oceans and decreased ocean pH. Although the continuation of these processes may alter the growth, survival, and diversity of marine organisms that synthesize CaCO₃ shells, the effects of ocean acidification since the dawn of the industrial revolution are not clear. Here we present experiments that examined the effects of the ocean’s past, present, and future (21st and 22nd centuries) CO₂ concentrations on the growth, survival, and condition of larvae of two species of commercially and ecologically valuable bivalve shellfish (Mercenaria mercenaria and Argopecten irradians). Larvae grown under near preindustrial CO₂ concentrations (250 ppm) displayed significantly faster growth and metamorphosis as well as higher survival and lipid accumulation rates compared with individuals reared under modern day CO₂ levels. Bivalves grown under near preindustrial CO₂ levels displayed thicker, more robust shells than individuals grown at present CO₂ concentrations, whereas bivalves exposed to CO₂ levels expected later this century had shells that were malformed and eroded. These results suggest that the ocean acidification that has occurred during the past two centuries may be inhibiting the development and survival of larval shellfish and contributing to global declines of some bivalve populations.
8. 2010: Kroeker, Kristy J., et al. “Meta‐analysis reveals negative yet variable effects of ocean acidification on marine organisms.” Ecology letters 13.11 (2010): 1419-1434. Ocean acidification is a pervasive stressor that could affect many marine organisms and cause profound ecological shifts. A variety of biological responses to ocean acidification have been measured across a range of taxa, but this information exists as case studies and has not been synthesized into meaningful comparisons amongst response variables and functional groups. We used meta‐analytic techniques to explore the biological responses to ocean acidification, and found negative effects on survival, calcification, growth and reproduction. However, there was significant variation in the sensitivity of marine organisms. Calcifying organisms generally exhibited larger negative responses than non‐calcifying organisms across numerous response variables, with the exception of crustaceans, which calcify but were not negatively affected. Calcification responses varied significantly amongst organisms using different mineral forms of calcium carbonate. Organisms using one of the more soluble forms of calcium carbonate (high‐magnesium calcite) can be more resilient to ocean acidification than less soluble forms (calcite and aragonite). Additionally, there was variation in the sensitivities of different developmental stages, but this variation was dependent on the taxonomic group. Our analyses suggest that the biological effects of ocean acidification are generally large and negative, but the variation in sensitivity amongst organisms has important implications for ecosystem responses.
9. 2012: Narita, Daiju, Katrin Rehdanz, and Richard SJ Tol. “Economic costs of ocean acidification: a look into the impacts on global shellfish production.” Climatic Change 113.3-4 (2012): 1049-1063. Ocean acidification is increasingly recognized as a major global problem. Yet economic assessments of its effects are currently almost absent. Unlike most other marine organisms, mollusks, which have significant commercial value worldwide, have relatively solid scientific evidence of biological impact of acidification and allow us to make such an economic evaluation. By performing a partial-equilibrium analysis, we estimate global and regional economic costs of production loss of mollusks due to ocean acidification. Our results show that the costs for the world as a whole could be over 100 billion USD with an assumption of increasing demand of mollusks with expected income growths combined with a business-as-usual emission trend towards the year 2100. The major determinants of cost levels are the impacts on the Chinese production, which is dominant in the world, and the expected demand increase of mollusks in today’s developing countries, which include China, in accordance with their future income rise. Our results have direct implications for climate policy. Because the ocean acidifies faster than the atmosphere warms, the acidification effects on mollusks would raise the social cost of carbon more strongly than the estimated damage adds to the damage costs of climate change.
10. 2013: Andersson, Andreas J., and Dwight Gledhill. “Ocean acidification and coral reefs: effects on breakdown, dissolution, and net ecosystem calcification.” Annual Review of Marine Science 5 (2013): 321-348. The persistence of carbonate structures on coral reefs is essential in providing habitats for a large number of species and maintaining the extraordinary biodiversity associated with these ecosystems. As a consequence of ocean acidification (OA), the ability of marine calcifiers to produce calcium carbonate (CaCO₃) and their rate of CaCO₃production could decrease while rates of bioerosion and CaCO₃ dissolution could increase, resulting in a transition from a condition of net accretion to one of net erosion. This would have negative consequences for the role and function of coral reefs and the eco-services they provide to dependent human communities. In this article, we review estimates of bioerosion, CaCO₃ dissolution, and net ecosystem calcification (NEC) and how these processes will change in response to OA. Furthermore, we critically evaluate the observed relationships between NEC and seawater aragonite saturation state (Ω_a). Finally, we propose that standardized NEC rates combined with observed changes in the ratios of dissolved inorganic carbon to total alkalinity owing to net reef metabolism may provide a biogeochemical tool to monitor the effects of OA in coral reef environments.
11. Ekstrom, Julia A., et al. “Vulnerability and adaptation of US shellfisheries to ocean acidification.” Nature Climate Change 5.3 (2015): 207-214.  Ocean acidification is a global, long-term problem whose ultimate solution requires carbon dioxide reduction at a scope and scale that will take decades to accomplish successfully. Until that is achieved, feasible and locally relevant adaptation and mitigation measures are needed. To help to prioritize societal responses to ocean acidification, we present a spatially explicit, multidisciplinary vulnerability analysis of coastal human communities in the United States. We focus our analysis on shelled mollusc harvests, which are likely to be harmed by ocean acidification. Our results highlight US regions most vulnerable to ocean acidification (and why), important knowledge and information gaps, and opportunities to adapt through local actions. The research illustrates the benefits of integrating natural and social sciences to identify actions and other opportunities while policy, stakeholders and scientists are still in relatively early stages of developing research plans and responses to ocean acidification.
12. Nagelkerken, Ivan, et al. “Ocean acidification alters fish populations indirectly through habitat modification.” Nature Climate Change 6.1 (2016): 89.  Ocean ecosystems are predicted to lose biodiversity and productivity from increasing ocean acidification¹. Although laboratory experiments reveal negative effects of acidification on the behaviour and performance of species^2,3, more comprehensive predictions have been hampered by a lack of in situ studies that incorporate the complexity of interactions between species and their environment. We studied CO₂ vents from both Northern and Southern hemispheres, using such natural laboratories⁴ to investigate the effect of ocean acidification on plant–animal associations embedded within all their natural complexity. Although we substantiate simple direct effects of reduced predator-avoidance behaviour by fishes, as observed in laboratory experiments, we here show that this negative effect is naturally dampened when fish reside in shelter-rich habitats. Importantly, elevated CO₂ drove strong increases in the abundance of some fish species through major habitat shifts, associated increases in resources such as habitat and prey availability, and reduced predator abundances. The indirect effects of acidification via resource and predator alterations may have far-reaching consequences for population abundances, and its study provides a framework for a more comprehensive understanding of increasing CO₂ emissions as a driver of ecological change.
13. Gibbs, Samantha J., et al. “Ocean warming, not acidification, controlled coccolithophore response during past greenhouse climate change.” Geology 44.1 (2016): 59-62.  Current carbon dioxide emissions are an assumed threat to oceanic calcifying plankton (coccolithophores) not just due to rising sea-surface temperatures, but also because of ocean acidification (OA). This assessment is based on single species culture experiments that are now revealing complex, synergistic, and adaptive responses to such environmental change. Despite this complexity, there is still a widespread perception that coccolithophore calcification will be inhibited by OA. These plankton have an excellent fossil record, and so we can test for the impact of OA during geological carbon cycle events, providing the added advantages of exploring entire communities across real-world major climate perturbation and recovery. Here we target fossil coccolithophore groups (holococcoliths and braarudosphaerids) expected to exhibit greatest sensitivity to acidification because of their reliance on extracellular calcification. Across the Paleocene-Eocene Thermal Maximum (56 Ma) rapid warming event, the biogeography and abundance of these extracellular calcifiers shifted dramatically, disappearing entirely from low latitudes to become limited to cooler, lower saturation-state areas. By comparing these range shift data with the environmental parameters from an Earth system model, we show that the principal control on these range retractions was temperature, with survival maintained in high-latitude refugia, despite more adverse ocean chemistry conditions. Deleterious effects of OA were only evidenced when twinned with elevated temperatures.
14. Speers, Ann E., et al. “Impacts of climate change and ocean acidification on coral reef fisheries: an integrated ecological–economic model.” Ecological economics 128 (2016): 33-43.  Coral reefs are highly productive shallow marine habitats at risk of degradation due to CO₂-mediated global ocean changes, including ocean acidification and rising sea temperature. Consequences of coral reef habitat loss are expected to include reduced reef fisheries production. To our knowledge, the welfare impact of reduced reef fish supply in commercial markets has not yet been studied. We develop a global model of annual demand for reef fish in regions with substantial coral reef area and use it to project potential consumer surplus losses given coral cover projections from a coupled climate, ocean, and coral biology simulation (CO₂-COST). Under an illustrative high emission scenario (IPCC RCP 8.5), 92% of coral cover is lost by 2100. Policies reaching lower radiative forcing targets (e.g., IPCC RCP 6.0) may partially avoid habitat loss, thereby preserving an estimated $14 to $20 billion in consumer surplus through 2100 (2014$ USD, 3% discount). Avoided damages vary annually, are sensitive to biological assumptions, and appear highest when coral ecosystems have moderate adaptive capacity. These welfare loss estimates are the first to monetize ocean acidification impacts to commercial finfisheries and complement the existing estimates of economic impacts to shellfish and to coral reefs generally.
15. Anthony, Kenneth RN. “Coral reefs under climate change and ocean acidification: challenges and opportunities for management and policy.” Annual Review of Environment and Resources 41 (2016): 59-81.  Carbon emissions in an industrialized world have created two problems for coral reefs: climate change and ocean acidification. Climate change drives ocean warming, which impacts biological and ecological reef processes, triggers large-scale coral bleaching events, and fuels tropical storms. Ocean acidification slows reef growth, alters competitive interactions, and impairs population replenishment. For managers and policymakers, ocean warming and acidification represent an almost paradoxical challenge by eroding reef resilience and simultaneously increasing the demand for reef resilience. Here, I address this problem in the context of challenges and potential solutions. Management efforts can compensate for reduced coral reef resilience in the face of global change, but to a limited extent and over a limited time frame. Critically, a realistic perspective on what sustainability measures can be achieved for coral reefs in the face of ocean warming and acidification is important to avoid setting unachievable goals for regional and local-scale management programs.
16. Sunday, Jennifer M., et al. “Ocean acidification can mediate biodiversity shifts by changing biogenic habitat.” Nature Climate Change 7.1 (2017): 81.  The effects of ocean acidification (OA) on the structure and complexity of coastal marine biogenic habitat have been broadly overlooked. Here we explore how declining pH and carbonate saturation may affect the structural complexity of four major biogenic habitats. Our analyses predict that indirect effects driven by OA on habitat-forming organisms could lead to lower species diversity in coral reefs, mussel beds and some macroalgal habitats, but increases in seagrass and other macroalgal habitats. Available in situ data support the prediction of decreased biodiversity in coral reefs, but not the prediction of seagrass bed gains. Thus, OA-driven habitat loss may exacerbate the direct negative effects of OA on coastal biodiversity; however, we lack evidence of the predicted biodiversity increase in systems where habitat-forming species could benefit from acidification. Overall, a combination of direct effects and community-mediated indirect effects will drive changes in the extent and structural complexity of biogenic habitat, which will have important ecosystem effects.
17. Hoegh-Guldberg, Ove, et al. “Coral reef ecosystems under climate change and ocean acidification.” Frontiers in Marine Science 4 (2017): 158.  Coral reefs are found in a wide range of environments, where they provide food and habitat to a large range of organisms as well as providing many other ecological goods and services. Warm-water coral reefs, for example, occupy shallow sunlit, warm, and alkaline waters in order to grow and calcify at the high rates necessary to build and maintain their calcium carbonate structures. At deeper locations (40–150 m), “mesophotic” (low light) coral reefs accumulate calcium carbonate at much lower rates (if at all in some cases) yet remain important as habitat for a wide range of organisms, including those important for fisheries. Finally, even deeper, down to 2,000 m or more, the so-called “cold-water” coral reefs are found in the dark depths. Despite their importance, coral reefs are facing significant challenges from human activities including pollution, over-harvesting, physical destruction, and climate change. In the latter case, even lower greenhouse gas emission scenarios (such as Representative Concentration Pathway RCP 4.5) are likely drive the elimination of most warm-water coral reefs by 2040–2050. Cold-water corals are also threatened by warming temperatures and ocean acidification although evidence of the direct effect of climate change is less clear. Evidence that coral reefs can adapt at rates which are sufficient for them to keep up with rapid ocean warming and acidification is minimal, especially given that corals are long-lived and hence have slow rates of evolution. Conclusions that coral reefs will migrate to higher latitudes as they warm are equally unfounded, with the observations of tropical species appearing at high latitudes “necessary but not sufficient” evidence that entire coral reef ecosystems are shifting. On the contrary, coral reefs are likely to degrade rapidly over the next 20 years, presenting fundamental challenges for the 500 million people who derive food, income, coastal protection, and a range of other services from coral reefs. Unless rapid advances to the goals of the Paris Climate Change Agreement occur over the next decade, hundreds of millions of people are likely to face increasing amounts of poverty and social disruption, and, in some cases, regional insecurity.