New Coral Family Identified in Atlantic

John Roach
for National Geographic News
February 25, 2004
Until now, all Atlantic coral families were believed to be close relatives to distinct coral families in the Pacific Ocean. But a new study for the first time identifies a family of corals found only in the Atlantic.

According to the study, at least one third of the corals that thrive in the Atlantic Ocean are free of any family ties to corals in the Pacific Ocean. The study could transform how the marine organisms are viewed, classified, and conserved.

Using modern DNA analysis techniques, an international team of scientists found that at least a third of the corals in the Atlantic are more closely related to each other than to their supposed Pacific Ocean mates.

Moreover, the analysis shows that some Pacific corals thought to belong to distinct family groups are in fact quite similar to each other and are likely all members of the same family.

"The standard taxonomy has been established for a hundred years, and this turns it on its head," said Nancy Knowlton, a marine biologist with the Scripps Institution of Oceanography at the University of California, San Diego.

Knowlton, who is a member of the National Geographic Society's Committee for Research and Exploration, directed the study, which will be published in tomorrow's issue of the science journal Nature.

Calculating just when the Atlantic lineage originated is difficult, according to the researchers, because their study calls into question the identity of many fossil corals. However, the best records indicate that the dominant Atlantic and Pacific lineages probably separated more than 34 million years ago.

Isabelle Côté, a biologist at the University of East Anglia in Norwich, England, who has studied coral reefs in the Caribbean, said she is surprised and fascinated by the finding of a unique lineage in the Atlantic.

"Like most other people, I went along with the taxonomic classification which is based mainly on morphology," she said.

Physically Similar

Knowlton said it is easy to understand how the differences between corals in the Pacific and Atlantic went undetected for more than a century: They all look about the same. And looks—or morphology—is how the corals were traditionally classified.

"This study highlights how misleading it can be to rely only on morphology and appearance to make inferences about patterns of speciation and evolution," Côté said.

After Knowlton and her colleagues discovered the differences between the corals through DNA analysis, they examined thin slices of the various corals and found physical distinctions in how the corals construct their walls.

For example, some corals build their walls via a wall-thickening process, whereas other corals build their walls via the insertion of crossbar-like skeletal structures. Once the walls are constructed, however, all the corals look virtually identical.

In future work Knowlton and study co-author Ann Budd of the University of Iowa in Iowa City will re-analyze the morphology of coral colonies to determine what characters to use to classify the marine organisms. These wall-building differences may be the key.

"We need to be able to say this family is characterized by this morphology so we can say which is which," Knowlton said. "But we can't do that now because the whole system is broken."

Coral Conservation

In addition to forcing scientists to rewrite the long-accepted coral classification system, the finding of a distinct coral family in the Atlantic should force conservationists to rethink their coral preservation strategy, according to the study authors.

Currently the bulk of conservation efforts are focused on species-rich coral reef ecosystems in the Pacific, overlooking most of the Caribbean region of the Atlantic, owing to its lack of unique families and low species diversity.

The finding that at least one third of the Atlantic corals are endemic to the Atlantic means conservationists should not write off the Atlantic just because it has a fewer number of coral species.

"We need to rethink how we identify places for high-priority conservation, because there is a lot more to diversity than species number," Knowlton said.

Côté, whose research has documented the rapid rate of coral decline in the Caribbean, agrees. "Given the fact that Atlantic corals are under tremendous pressures from human activities—perhaps more so than those in most of the Indo-Pacific—this is a timely and important piece of research," she said.

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