Cool, Deep Waves May Save Coral Reefs from Heat Stress

Corals don't do well in the heat. Increased water temperatures can lead to bleaching events with sometimes fatal consequences. Now, though, scientists have found that in the Andaman Sea, internal waves can temporarily cool down the water temperature around corals by up to ten degrees, which could save reefs.

In 1991, 1995, 2003 and 2010, bleaching events occurred for corals within the Andaman Sea.  Yet 2010 was the worst, hitting corals hard and causing extensive damage. That's why researchers decided to examine this region a bit more closely to see exactly how the corals fared in order to see what might be in store for the future.

The scientists analyzed how the location of reefs determined the extent of the damage; they found that locations that faced westward benefitted from so-called large-amplitude internal waves (LAIW). In contrast to surface waves, LAIW travel along density gradients that separate the cold deep water from the warmer upper layer. Once they reach the continental shelf, these waves may break and transport water from the deep to the shallow coral reefs and effectively cool them.

Needless to say, these westward-facing reefs did far better than those that were sheltered by islands.

"These changes are a mixed blessing," said Claudio Richter, the project leader, in a news release. "Under normal conditions, lower temperatures have negative effects on the corals. But during heat stress, they offer unexpected cooling and help the corals to survive."

The findings reveal exactly how these corals can survive warmer temperatures. This could be important in the future as the climate continues to change. More specifically, it could allow local researches to better monitor local reefs and protect them in the future.

The findings are published in the journal Proceedings of the Royal Society B.

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