How does rising atmospheric CO2 affect marine organisms?

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Hot-Water Climate-Change Refugia for Corals?
Van Woesik, R., Houk, P., Isechal, A.L., Idechong, J.W., Victor, S. and Golbuu, Y. 2012. Climate-change refugia in the sheltered bays of Palau: analogs of future reefs. Ecology and Evolution 2: 2474-2484.

The authors write that "coral bleaching and mortality are predicted to increase as climate change-induced thermal-stress events become more frequent," but they say that "few studies have examined deviations from the expected positive relationships among thermal stress, coral bleaching, and coral mortality."

What was done
To help fill this data void, van Woesik et al. examined the response of more than 30,000 - yes, that's thirty thousand - coral colonies at 80 sites in Palau, during a regional thermal-stress event in 2010, seeking to determine "whether any habitats were comparatively resistant to thermal stress."

What was learned
The six scientists discovered that (1) "bleaching was most severe in the northwestern lagoon, in accordance with satellite-derived maximum temperatures and anomalous temperatures above the long-term averages," that (2) corals there "suffered the most extensive bleaching and the highest mortality," but that (3) "in the bays where temperatures were higher than elsewhere, bleaching and mortality were low." As for why this was so, they suggest that "constant exposure to high temperatures, and high vertical attenuation of light caused by naturally high suspended particulate matter buffered the corals in bays from the 2010 regional thermal-stress event."

What it means
In concluding their paper, van Woesik et al. say their study shows that "reefs around bays were more resistant to regional thermal stress than patch and outer reefs," and that "nearshore reefs in the bays are therefore valuable refuges to buffer coral-reef ecosystems against climate change-induced disturbances," and that they thus "should be given high conservation status because they provide refugia for coral populations as the oceans continue to warm."

Reviewed 26 June 2013