Science: Mar 10, 2012

WASHINGTON: Global warming is a serious threat to coral reefs, but fortunately a new study has revealed that some coral species may adapt to warmer oceans.

An international team of researchers reports that coral populations, who unexpectedly survived a massive bleaching event in 2010 in South-East Asia, water previously experienced severe bleaching during an event in 1998.

The team analyzed what happened in three places during the 2010 event and found that in Indonesia, corals responded to high sea temperatures in a typical way, with a rapid increase in branching species - such as staghorn corals - are suffering a severe die-offs.

But in areas controlled in Singapore and Malaysia, the usual trend was reversed: a normally susceptible colonies of Acropora corals rapid growth appeared healthy and fully pigmented, while most colonies of massive coral was severely bleached.

"Mass coral bleaching events, caused by breakdown in the relationship between coral animals and their symbiotic algae, is closely linked with an unusually high ocean temperatures and have led to an extensive reef degradation in the last few decades," explained lead author Dr. James Guest, now a common research fellow at the UNSW Centre Marine Bio-innovation, and the Advanced Environmental Biotechnology Centre in Singapore, the Nanyang Technological University.

"The importance of these events varies considerably, but so far we have seen a consistent trend: some types of coral tend to be more resistant to bleaching than others. This has led to the prediction that hardier, slower growing massive species replace less robust, fast-growing branching species on reefs in the future.

"But during the 2010 event the normal hierarchy of species susceptibility was reversed in some places. Corals to our Indonesian study site in Pulau Weh, Sumatra, followed the usual pattern, with about 90 percent of colonies of fast growing species to die.

"But the pattern was the opposite of the study sites in Singapore and Malaysia, although sea temperature data showed that the magnitude of thermal stress was similar in all places.

"This suggests that the thermal history of these places can be played an important role to determine the bleaching severity in 2010.

"When we looked at archived sea-surface temperature data and past bleaching records we found that the places that had a reversed hierarchy of susceptibility and less severe bleaching in 2010 also bleached during 1998. In contrast, the place that had a normal bleaching hierarchy and severe bleaching will not bleach in 1998.

"The most parsimonious explanation, therefore, is that coral populations that bleached during the last major warming event in 1998, adapted and / or acclimatised to heat stress. This is controversial because many scientists believe that coral has exhausted its capacity to adapt to thermal stress," he said.

While these results are encouraging, Dr. Guest said, it does not necessarily mean that the global threat to reefs has declined.

There are probably limits to thermal adaptation and acclimatization, and there may be other costs for the corals, such as reduced growth and reproductive health. In turn, reefs continue to threaten to over fishing, pollution, disease and ocean acidification.

"The results of the present study do indicate, however, that the effects of coral bleaching will not be as uniform as previously thought, and fast-growing branching taxa such as Acropora and Pocillopora are likely to persist in some areas in spite of increases in the frequency of heat stress events," Dr. Guest concluded.

The study was published in the journal PLoS One.

Science

Saturday, March 10, 2012

Some coral species may be able to adapt to global warming

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