Coral resistance to ocean acidification linked to increased calcium at the site of calcification

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Abstract

Ocean acidification threatens the persistence of biogenic calcium carbonate (CaCO 3) production on coral reefs. However, some coral genera show resistance to declines in seawater pH, potentially achieved by modulating the chemistry of the fluid where calcification occurs. We use two novel geochemical techniques based on boron systematics and Raman spectroscopy, which together provide the first constraints on the sensitivity of coral calcifying fluid calcium concentrations ( <img alt="" class="inline-figure" src="/document_file/4327e40c-ba16-4e92-bf79-e018d0bf7af4/PubMedCentral/image/rspb20180564-i1.jpg"/> ) to changing seawater pH. In response to simulated end-of-century pH conditions, Pocillopora damicornis increased <img alt="" class="inline-figure" src="/document_file/4327e40c-ba16-4e92-bf79-e018d0bf7af4/PubMedCentral/image/rspb20180564-i2.jpg"/> to as much as 25% above that of seawater and maintained constant calcification rates. Conversely, Acropora youngei displayed less control over <img alt="" class="inline-figure" src="/document_file/4327e40c-ba16-4e92-bf79-e018d0bf7af4/PubMedCentral/image/rspb20180564-i3.jpg"/> , and its calcification rates strongly declined at lower seawater pH. Although the role of <img alt="" class="inline-figure" src="/document_file/4327e40c-ba16-4e92-bf79-e018d0bf7af4/PubMedCentral/image/rspb20180564-i4.jpg"/> in driving calcification has often been neglected, increasing <img alt="" class="inline-figure" src="/document_file/4327e40c-ba16-4e92-bf79-e018d0bf7af4/PubMedCentral/image/rspb20180564-i5.jpg"/> may be a key mechanism enabling more resistant corals to cope with ocean acidification and continue to build CaCO 3 skeletons in a high-CO 2 world.

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Ocean acidification causes bleaching and productivity loss in coral reef builders.

K. R. N. Anthony, D. I. Kline, G. Diaz-Pulido … (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 CO(2) 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 CO(2) is a bleaching agent for corals and CCA under high irradiance, acting synergistically with warming to lower thermal bleaching thresholds. We propose that CO(2) 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 CO(2) scenario led to a 30% increase in productivity in Acropora, whereas high CO(2) lead to zero productivity in both corals. CCA were most sensitive to acidification, with high CO(2) 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.

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Marine calcifiers exhibit mixed responses to CO2-induced ocean acidification

J. Ries, A Cohen, D. C. McCorkle (2009)

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The geological record of ocean acidification.

Bärbel Hönisch, Andy Ridgwell, Daniela N Schmidt … (2012)

Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO(2), global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry-a consequence of the unprecedented rapidity of CO(2) release currently taking place.