Corals Moving North to Escape Warming

A 'high priority' coral reef near southern Tanzania. CREDIT: T.McClanahan/Wildlife Conservation Society. View full size image

Corals may be dying in tropical areas, but now it appears they are expanding their range poleward, scientists find.

Corals are critical to ocean life, forming reefs that are home to a dazzling array of species. Despite occupying less than 1 percent of the ocean floor — an area about half the size of France — temperate and tropical reefs provide a home for as much as 25 percent of the world's marine species. Only tropical rain forests can compete with the sheer concentration of biodiversity found in coral reefs.

Unfortunately, corals are especially vulnerable to changes in temperature. As the oceans warm due to Earth's changing climate, corals are dying in tropical areas where the warm waters cause them to expel the symbiotic algae that provide them with nutrients — a process called bleaching .

However, this warming could give corals opportunities as well. Scientists find that as temperatures in higher latitudes rise, coral are expanding poleward.

Geographer Hiroya Yamano, at the National Institute for Environmental Studies in Tsukuba, Japan, and his colleagues investigated 80 years of national records from temperate areas around Japan. Wintertime sea surface temperatures rose by as much as 4.3 degrees Fahrenheit (2.4 degrees Celsius) in those sites during that period.

The scientists found that four of the nine coral species they studied in these areas in the Northern Hemisphere expanded their range northward since the 1930s as quickly as 8.7 miles (14 kilometers) per year. None of the coral species went south toward the tropics.

"I find the speed — 14 kilometers per year — is stunning," Yamano told OurAmazingPlanet.

These findings might be good news for corals, "but for corals only," Yamano said. Other research suggests that warming waters might spur exotic species to invade new areas, which could negatively impact native marine species.

"Further, even if range expansion of corals does occur, the amount of dying corals in tropical areas may be much greater than the new settlements in the temperate regions," Yamano added.

Yamano added this research only looked at occurrence of corals, not at their abundance. The team will launch a monitoring program to examine settlement and growth of corals at a number of sites to get a better picture of how corals are shifting, he said.

Yamano and his colleagues Kaoru Sugihara and Keiichi Nomura detailed their findings online Feb. 17 in the journal Geophysical Review Letters.

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