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Surviving Coral Bleaching
Volume 17, Number 21: 21 May 2014

In a new study recently published in the journal PLOS ONE, Cantin and Lough (2014) write that the Great Barrier Reef (GBR) of Australia "experienced high thermal stress and observations of significant coral bleaching in the summers of 1998 and 2002, with 42% and 54%, respectively, of the reef showing some degree of bleaching," citing in this regard the descriptive work of Berkelmans et al. (2004), while stating that the purpose of their newer study was "to determine what, if any, signatures of these 1998 and 2002 mass coral bleaching events are evident in the annual growth records contained in coral cores from apparently healthy massive Porites colonies from four reef sites in the central GBR that survived the worst bleaching events ever recorded in the GBR." And this they did by assessing annual growth characteristics (extension, density and calcification) of 144 cores that they extracted from 79 coral colonies covering the 24-year period 1980-2003.

As for what they learned from this undertaking, the two researchers indicate, first of all, that following the 2002 bleaching event, there has not been an additional such event, after which they state that "while these events caused widespread bleaching on more than 50% of the GBR, over a short four-year period, our results indicate two major findings: 1) the frequency of severe temperature stress at individual sites has not yet increased as projected, and 2) calcification rates recovered from the effects of severe bleaching within 4 years and have not continued to decline."

With respect to the significance of these findings, Cantin and Lough write in the concluding sentence of their paper that "these two observations in combination with future efforts to update calcification trends for the GBR that include the last decade following the 2002 event will provide significant advances that will better inform models that project how coral calcification will respond to ongoing warming of the tropical oceans."

And if the past is prologue to the future, what they have learned to date is most encouraging.

Sherwood, Keith and Craig Idso

Berkelmans, R., De'ath, G., Kininmonth, S. and Skirving, W. 2004. A comparison of the 1998 and 2002 coral bleaching events on the Great Barrier Reef: spatial correlation, patterns and predictions. Coral Reefs 23: 74-83.

Cantin, N.E. and Lough, J.M. 2014. Surviving coral bleaching events: Porites growth anomalies on the Great Barrier Reef. PLOS ONE 9: e88720.