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448919 
Journal Article 
Ocean acidification causes bleaching and productivity loss in coral reef builders 
Anthony, KRN; Kline, DI; Diaz-Pulido, G; Dove, S; Hoegh-Guldberg, O 
2008 
1 
Proceedings of the National Academy of Sciences of the United States of America
ISSN: 0027-8424
EISSN: 1091-6490 
105 
45 
17442-17446 
English 
18988740 
WOS:000260981800051 
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. 
climate change; global warming; carbon dioxide; Great Barrier Reef; co2 partial-pressure; great-barrier-reef; climate-change; excitation; pressure; scleractinian coral; carbonate chemistry; calcification rate; anthropogenic co2; photosynthesis; light