How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

The Flip Side of Coral Bleaching
Mondal, T., Raghunathan, C. and Venkataraman, K. 2013. Bleaching: The driving force of scleractinian new recruitment at Little Andaman Island, Andaman and Nicobar Islands. Proceedings of the National Academy of Sciences, India, Section B Biological Sciences 83: 585-592.

Little Andaman Island, located at the juncture of the Bay of Bengal and the Andaman Sea, had a limited number of fringing reefs that were essentially destroyed when a 2004 tsunami swept across them with devastating consequences. Five years later in 2009, however, 34 species of scleractinian corals had reappeared, as reported by Sawall et al. (2010). But the very next year there was a massive bleaching event caused by a dramatic increase in sea surface temperatures above their normal average ranges (Mondal and Raghunathan, 2011), after which it was found, in the words of the authors, that "the bleached corals were transformed mostly into dead ones."

What was done
Curious as to what the biological legacy of this latter devastating phenomenon might be, Mondal et al., in February 2012, employed Self Contained Underwater Breathing Apparatus (SCUBA) gear to dive to depths of up to 35 meters to identify and record what species of scleractinian corals they might encounter at three different locations around Little Andaman Island, employing the Line Intercept Transect Method (Bradbury et al., 1886) with a series of 20-meter transects randomly placed at intervals of 10 meters, with three replicates of the procedure carried out at depths of 5, 10, 15, 20, 25, 30 and 35 meters.

What was learned
The three Indian researchers discovered a total of 124 species of youthful scleractinian corals, which was 90 more than the 34 species detected by Sawall et al. (2010). In addition, they say that the minimum value of the Shannon-Weaver Diversity Index was 5.09, which they added "is above the optimum hypothetical value," and that the minimum value of Simpson's Density Index was 0.94, which they said "is very near to the maximum value which is most advantageous."

What it means
In light of these dramatic observations, plus the fact that "bleaching was the only physiological process which happened in between 2009 and 2012," Mondal et al. wrote that "bleaching is a prime regulator for the settlement of new recruitment of scleractinian corals which leads to diversified reef area," while further noting that "the adaptive features of bleaching can be seen as a mechanism that enables the exchange of symbionts in a better fit of the holobiont to a changed environment," additionally citing in this regard the study of Graham et al. (2011).

Bradbury, R.H., Reichelt, R.E., Meyer, D.L. and Birtles, R.A. 1886. Patterns in the distribution of crinoid community at Davies Reef on the central Great Barrier Reef. Coral Reefs 5: 189-196.

Graham, N.A.J., Nash, K.L. and Kool, J.T. 2011. Coral reef recovery dynamics in a changing world. Coral Reefs 30: 283-294.

Mondal, T. and Raghunathan, C. 2011. An observation on the coral bleaching in Andaman Islands. International Journal of Environmental Science 1: 37-51.

Sawall, Y., Phongsuwan, N. and Richter, C. 2010. Coral recruitment and recovery after the 2004 tsunami around the Phi Phi Islands (Krabi Province) and Phuket, Andaman Sea, Thailand. Helgoland Marine Research 64: 357-365.

Reviewed 1 January 2014