Corals Moving North

As oceans warm, reefs off Japan shift to higher latitudes.

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By Marissa Cevallos, Science News

Some Pacific corals have done the equivalent of moving from sunny Atlanta to Detroit, possibly in response to rising ocean temperatures.

A new study of reefs around Japan reveals that a handful of coral species have migrated from the balmy subtropics to temperate climate zones over the last 80 years. The study is the first to track coral reefs for such a long time and over several latitude lines, a Japanese team reports in an upcoming Geophysical Research Letters.

The team, led by geographer Hiroya Yamano of the National Institute for Environmental Studies in Tsukuba, Japan, analyzed maps of corals from four time periods starting in the 1930s. They found that of nine common coral species, four had expanded northward, and two went as far as temperate waters. The study confirms what marine biologists and fishermen have speculated for years. “There were eyewitness accounts of the occurrence, but the data wasn’t so reliable,” says Yamano. “Now we can show very solid evidence.”

Now it appears that some coral species will migrate—and fast—in response to warming waters. Some species Yamano examined migrated as fast as 8.7 miles per year. Yamano calculated that a sample of land-traveling animals migrate only 0.4 miles per year on average. In 80 years, the fastest corals would travel nearly 700 miles. It would be like land plants making the Atlanta-to-Detroit trek between the Great Depression and today.

Coral reefs are important biologically because they house a diverse group of animals—about one in four marine species call a coral reef home. Reefs are made of animals called polyps with a hard skeleton made of calcium carbonate. Each year, the corals around Japan hatch larvae, which can get swept up by warm Pacific currents from the south called Kuroshio and >Tsushima currents. But most larvae normally don’t settle far from home.

Taken with other studies that report animals moving north as temperature rises, it’s a good hypothesis that the corals in this study are moving to fight the heat, says John Pandolfi, a marine biologist at the University of Queensland in Brisbane, Australia. Researchers will next need to study these species in the lab to test whether temperature is truly the culprit.

But adjusting the marine thermostat isn’t the only way to kill a coral. Too much acidity from high concentrations of carbon dioxide can also weaken coral reefs. So it’s peculiar that the Japanese corals moved north, says Pandolfi, because their new homes are likely more saturated with carbon dioxide. It appears corals are able and willing to make that trade-off, he says.

Studies like this one will be crucial for creating a global database of how marine life is reacting to climate change, says Pandolfi. He and his colleagues are collating studies for such a data repository right now. Species all react differently to changes in temperature, and it’s difficult to figure out from the published literature which ones stay put.

“The good thing about this study, they didn’t just tell us what moved, but what didn’t move,” says Pandolfi. He says one pitfall in drawing data from a pool of research papers is that it’s harder to publish a study that shows no change in species movement, so data on those species are often not available.

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