Coral reefs ‘adapt to climate change’

Bleached coral Copyright: NASA

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Tropical coral reefs may be less susceptible to climate change than previously thought, according to research published in Nature this week.

The study provides the first evidence that corals are able to adapt to ‘bleaching’, which occurs when increases in water temperature cause the death of microscopic algae living inside corals. Without the algae present, corals cannot survive.

Coral reefs provide habitat for about 25 per cent of the world’s marine species and generate some US$30 billion each year through fishing and tourism, according to the US National Oceanic and Atmospheric Administration (NOAA). They also protect shorelines from wave action, which can threaten property and human lives, particularly in the tropics.

Bleaching has increased in recent years and is thought to have killed off one-sixth of the world’s coral during the last major occurrence, which took place in 1998 (see Reef under threat from ‘bleaching’ outbreak).

The researchers, led by Andrew Baker from the Wildlife Conservation Society, compared the genetic makeup of algae in Panamanian reefs that had suffered bleaching during the 1998 event with those that had not been affected. They found after severe bleaching, corals have a higher proportion of heat tolerant forms of the algae.

Looking at reefs in the Middle East, the researchers found that the heat-tolerant algae dominated those in the Persian Gulf, which had been severely bleached in 1998 when sea temperatures in places reached 38 °C. In contrast, on reefs in the nearby Red Sea — where sea temperatures are typically 29 °C — the heat tolerant algae were rare.

When the researchers compared Kenyan reefs bleached in 1998 with those in Mauritius that escaped bleaching that year, they found the same pattern.

Coral reefs are both ecologically and economically important in tropical countries such as those studied. According to NOAA, coral reefs provide 25 per cent of fish produced in developing countries with reefs, and provide food for a billion people in Asia alone.

Although the researchers do not yet know what process causes the shift from one type of algae to another, their study suggests the change may allow reefs to resist future bleaching due to increases in sea temperature.

Link to full research paper by Baker et al in Nature.

Reference: Nature 430, 741 (2004)