Case study reference
| Spatial context
| Impact description (case study)
| Case study recommendations
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Guinotte, J. M., & Fabry, V. J. (2008). Ocean acidification and its potential effects on marine ecosystems. Annals of the New York Academy of Sciences, 1134(1), 320-342.
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Global
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A substantial decrease in the number of carbonate ions available in seawater will have serious implications for coral calcification rates and skeletal formation. This will lead to erosional processes to occur at much faster rates, and slower growth rates may also reduce corals' ability to compete for space and light. The net effect of ocean acidification on coral reef ecosystems will probably be negative as many reef-building marine calcifiers will be heavily impacted by the combined effects of increasing sea-surface temperatures (coral bleaching) and decreasing carbonate saturation states of surface waters in the coming decades.
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Future ocean acidification research needs include increased resources and efforts devoted to lab, mesocosm, and in situ experiments, all of which will aid in determining the biological responses of marine taxa to increased pCO2.
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Shaw, E. C., McNeil, B. I., & Tilbrook, B. (2012). Impacts of ocean acidification in naturally variable coral reef flat ecosystems. Journal of Geophysical Research: Oceans (1978-2012), 117(C3)
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Global
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Ocean acidification leads to changes in marine carbonate chemistry that are predicted to cause a decline in future coral reef calcification. Experiments and in situ studies on natural coral reefs have shown a direct relationship between aragonite saturation state (Omega(arag)) and net community calcification (G(net)). Measurements of extreme diurnal variability in carbonate chemistry within a reef flat in the southern Great Barrier Reef, Australia, showed that omega(arag) varied between 1.1 and 6.5, thus exceeding the magnitude of change expected this century in open ocean subtropical/ tropical waters. The observed variability comes about through biological activity on the reef, where changes to the carbonate chemistry are enhanced at low tide when reef flat waters are isolated from open ocean water. Net community calcification was found to be linearly related to Omega(arag), while temperature and nutrients had no significant effect on G(net). Net community calcification is thus projected to decline by 55% of its preindustrial value by the end of the century.
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It is not known at this stage whether exposure to large variability in carbonate chemistry will make reef flat organisms more or less vulnerable to the non-calcifying physiological effects of increasing ocean CO2 and future laboratory studies will need to incorporate this natural variability to address this question. Future work investigating the responses of different natural coral reef communities to carbonate chemistry will also be needed and an understanding of why the different systems show different responses will be required in order to make quantitative global predictions about coral reef responses to ocean acidification.
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Uthicke, S., & Fabricius, K. E. (2012). Productivity gains do not compensate for reduced calcification under near-future ocean acidification in the photosynthetic benthic foraminifer species Marginopora vertebralis. Global Change Biology, 18(9), 2781-2791.
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Australia / Oceania
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This study shows that endosymbiotic algae in foraminifera benefit from increased dissolved inorganic carbon (DIC) availability and may be naturally carbon limited. Productivity, respiration, and abundances of the symbiont-bearing foraminifer species Marginopora vertebralis on natural CO2 seeps in Papua New Guinea and production and calcification on the Great Barrier Reef (GBR) were studied using artificially enhanced pCO2.
Production of M.vertebralis increased with increasing light and increasing pCO2 and declined at higher temperatures. Respiration was also significantly elevated (similar to 25%), whereas calcification was reduced (1639%) at low pH/high pCO2 compared to present-day conditions. In the field, M. vertebralis was absent at three CO2 seep sites at pHTotal levels below similar to 7.9 (pCO2 similar to 700 similar to mu atm), but it was found in densities of over 1000 similar to m-2 at all three control sites.
The net outcome of these two competing processes is that M. vertebralis cannot maintain populations under pCO2 exceeding 700 and thus are likely to be extinct in the next century.
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To improve predictions of the ecological effects of ocean acidification, the net gains and losses between the processes of photosynthesis and calcification need to be studied jointly on physiological and population levels.
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Bates, N., Amat, A., & Andersson, A. (2010). Feedbacks and responses of coral calcification on the Bermuda reef system to seasonal changes in biological processes and ocean acidification. Biogeosciences, 7(8), 2509-2530.
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North Atlantic: The Islands of Bermuda
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Due to lower annual mean surface seawater [CO(3)(2-)] and Omega(aragonite) in Bermuda compared to tropical regions, we anticipate that Bermuda corals will experience seasonal periods of zero net calcification within the next decade at [CO(3)(2-)] and Omega(aragonite) thresholds of similar to 184 mu moles kg(-1) and 2.65. However, net autotrophy of the reef during winter and spring (as part of the CREF hypothesis) may delay the onset of zero NEC or decalcification going forward by enhancing [CO(3)(2-)] and Omega(aragonite). The Bermuda coral reef is one of the first responders to the negative impacts of ocean acidification, and we estimate that calcification rates for D. labyrinthiformis have declined by > 50% compared to pre-industrial times. The study also anticipates that the Bermuda coral reef (as well as other high latitude reefs) will likely be subjected to "seasonal decalcification" with wintertime decalcification occurring many decades before summertime decalcification.
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Manzello, D. (2010). Coral growth with thermal stress and ocean acidification: lessons from the eastern tropical Pacific. Coral Reefs, 29(3), 749-758.
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Central America / Caribbean: Panama
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The rapid growth of scleractinian corals is responsible for the persistence of coral reefs through time. Coral growth rates have declined over the past 30 years in the western Pacific, Indian, and North Atlantic Oceans. A multi-species inventory of coral growth from Pacific Panama confirms that declines have occurred in some, but not all species. Linear extension declined significantly in the most important reef builder of the eastern tropical Pacific, Pocillopora damicornis, by nearly one-third from 1974 to 2006. The rate of decline in skeletal extension for P. damicornis from Pacific Panama (0.9% year(-1)) was nearly identical to massive Porites in the Indo-Pacific over the past 20-30 years (0.89-1.23% year(-1)). The branching pocilloporid corals have shown an increased tolerance to recurrent thermal stress events in Panama, but appear to be susceptible to acidification. In contrast, the massive pavonid corals have shown less tolerance to thermal stress, but may be less sensitive to acidification. These differing sensitivities will be a fundamental determinant of eastern tropical Pacific coral reef community structure with accelerating climate change that has implications for the future of reef communities worldwide.
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