Some coral reefs adapting to global warming

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Although coral reefs are slowly dying from the effects of global warming, scientists have identified evidence that some reefs are adapting to higher temperatures and might actually survive global warming.

Publishing the results of their study in a recent issue of the journal Marine Ecology Progress Series, Thomas Oliver and Stephen Palumbi studied table-top acroporid corals in Palmyra Atoll, the central Philippines, Fiji and American Samoa.

Coral form symbiotic relationships with single-celled algae (zooxanthellae), a relationship broken by rising temperatures.

Bleaching

Higher temperatures stress the algae, causing them to stop producing food for the coral. This in turn leads to the coral ejecting the algae, dying and turning white in a process known as coral bleaching.

Previous studies had identified different strains of zooxanthellae, some of which are resistant to elevated temperatures.

Some corals are known to host these heat-resistant algae while others are known to swap heat-stressed algae for the heat-resistant strain with rising temperatures.

The authors examined the proportion of acroporid corals hosting heat-resistant zooxanthellae in Ofu Island in American Samoa and compared their distributions with water temperatures.

Heat resistance

They found that sites with higher maximum temperatures had higher proportions of heat-tolerant zooxanthellae.

However, when they compared their results with data from the other study sites, they found no such correlation at a wider scale across the Pacific.

Even though a simple explanation for the distribution of corals hosting heat-resistant zooxanthellae elude the authors, they stress that ...the identification of areas...that have high availability of stress tolerant may be important to policy makers.

These areas may better resist coming environmental changes and might serve managers as resilient ~fortresses of diversity around which to build their conservation strategy.

For more information, see the paper: Oliver, TA and SR Palumbi (2009) Distributions of stress-resistant coral symbionts match environmental patterns at local but not regional scales. Marine Ecology Progress Series 378, p. 93"103.