Some Good News for Coral Reefs, Maybe…

Posted by on March 14, 2012

14th March 2012.  Having posted just a few days ago, I was planning to develop some thoughts on ocean acidification to post in a week or so.  But then a news item caught my eye – some possible good news for the world’s coral reefs.

Thanks to a colleague’s post on coral-list, I learned about an article in Science Now, and the more detailed study in PLoS One.  Bear with me as I try and summarize.  An international team of nine researchers from Singapore, Indonesia, Malaysia, French Polynesia, Australia and the U.K. has reported that the branching coral genera, Acropora and Pocillopora,  normally highly susceptible to warming events, and therefore quick to bleach and to die, have proved more resistant than normally resistant genera like Porites during a severe bleaching event in 2010 in Singapore waters.  This is the first time such a “reversal” in sensitivity has been reported.

The extensive warming event and mass bleaching occurred during May and June 2010.  The team was able to survey sites at three locations: 1) Pulau Weh, north Sumatra, Indonesia, 2) Singapore, and 3) Tioman Island, south-east Malaysia, north of Singapore.  Surveys took place 21 to 25 weeks after the bleaching event at each location.  At Pulau Weh, the expected pattern of sensitivity was observed, with branching corals more severely impacted than the boulder-like Porites.  At Singapore, however, the reversed pattern occurred, while at Tioman Island the branching species were less impacted by the warming, although still more strongly impacted than Porites.

In their PLoS One paper, James Guest and his co-authors note that long-term temperature records show that Pulau Weh differs from the other two locations in having a more uniform temperature regime through time, and did not have a strong thermal anomaly during 1998.  Corals there are not reported to have bleached in 1998.  In 2010, In Pulau Weh, 94% of Acropora and 87% of Pocillopora colonies died following the bleaching event, compared to only 5% of Acropora and 12% of Pocillopora in Singapore.  Proportions dying were 28% and 36% respectively at Tioman Island, although these genera were still among the most heavily impacted there.

The team’s favored hypothesis to explain these contrasting results:  previous bleaching events at Singapore, and perhaps also at Tioman Island, have permitted development of resistance to warm water by these rapidly growing species of coral that also happen to have relatively short generation times (from spawning to maturity in as little as three years).  Previous workers have feared that corals would not be able to adapt to warmer temperatures because generation times were relatively long, and warming has been proceeding very rapidly.  Maybe, just maybe, there is a glimmer of hope for coral reefs.

But let’s not conclude from this study that there is no reason to worry about climate change after all.  At the same time that I learned about these corals, I learned that the North American Great Lakes are ceasing to be ice-covered in winter.  The CBC reports that a new study in the journal, Climate, by Jia Wang and co-workers at NOAA’s Great Lakes Environmental Lab, finds that the lake system has lost 71% of its usual winter ice cover over the 37 years between 1973 and 2010.  Tiny Lake St. Clair has shown the smallest change (37%) while Lake Ontario has lost the most (88%).  Global warming is still real, and changes of this magnitude must have significant effects on the biological productivity of these lakes.

And if that is not enough to diminish our general feeling of optimism about those Singaporean corals, a new report in Science News, summarized a series of presentations on effects of ocean acidification at the AAAS meeting in Vancouver last month.  Plenty of bad news to go round in that article, but I’ll pick that up when I talk about ocean acidification, soon.

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