How does rising atmospheric CO2 affect marine organisms?

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Corals Killed by Cooling
Reference
Yu, K.-F., Zhao, J.-X., Liu, T.-S., Wei, G.-J., Wang, P.X. and Collerson, K.D.  2004.  High-frequency winter cooling and reef coral mortality during the Holocene climatic optimum.  Earth and Planetary Science Letters 224: 143-155.

What was done
The authors extracted and analyzed various ecological, micro-structural and skeletal Sr/Ca data -- the latter of which correlate with sea surface temperature (SST) -- from a 3.42-m-thick Goniopora coral profile in an emerged Holocene reef terrace at Leizhou Peninsula in the northern South China Sea.

What was learned
The data revealed, in the words of Yu et al., that "at least nine abrupt massive Goniopora stress and mortality events occurred in winter during the 7.0-7.5 thousand calendar years before present."  These cooling-induced devastations occurred at approximately 50-year intervals, and they say "it took about 20-25 years for a killed Goniopora coral reef to recover."

What it means
In commenting on their findings, Yu et al. remark that "similar cold bleaching and mortality of branchy Acropora coral colonies occurred on 5 Aug 2003 at Heron Island, the southern end of the Great Barrier Reef (Hoegh-Guldberg, 2004), when local air temperatures dropped to as low as 12°C," and that "coral mortality occurred in the Arabian Sea when the monthly mean SST there dropped to < 13°C (Coles and Fadlallah, 1991)," which observations demonstrate that the cold bleaching of corals (Saxby et al., 2003) was not only not precluded by the warm temperatures of the Holocene Climatic Optimum, it is not precluded by the warm temperatures of today.  Also, in harmony with the findings of Halford et al. (2004), the results of this study demonstrate that coral reefs have an uncanny ability to successfully recover from the deleterious effects of seemingly devastating events.

References
Coles, S.L. and Fadlallah, Y.H.  1991.  Reef coral survival and mortality at low-temperatures in the Arabian gulf - new species-specific lower temperature limits.  Coral Reefs 9: 231-237.

Halford, A., Cheal, A.J., Ryan, D. and Williams, D.M.  2004.  Resilience to large-scale disturbance in coral and fish assemblages on the Great Barrier Reef.  Ecology 85: 1892-1905.

Hoegh-Guldberg, O.  2004.  Low temperatures cause coral bleaching.  Coral Reefs: in press.

Saxby, T., Dennison, W.C. and Hoegh-Guldberg, O.  2003.  Photosynthetic responses of the coral Montipora digitata to cold temperature stress.  Marine Ecology Progress Series 248: 85-97.


Reviewed 17 November 2004