New Expedition to Study Mysterious Deep-Sea Corals

Stefan Lovgren in Boston, Massachusetts
for National Geographic News
February 19, 2008
Some of Earth's most mysterious organisms—ancient corals that can be found 9,186 feet (2,800 meters) below the ocean's surface—will be the subject of an ambitious new research program, scientists have announced.

The Trans-Atlantic Coral Ecosystem Study, or TRACES, was officially launched last Friday at the annual meeting of the American Association for the Advancement of Science in Boston, Massachusetts.

It will be the first ocean-scale study of the poorly understood deep-sea corals, whose growth patterns may fill large gaps in researchers' knowledge of climate and the evolution of marine creatures.

Recent studies have shown some living deep-sea corals to be up to 5,000 years old, making them a detailed historical archive of changing sea conditions and climates, researchers say.

At the meeting scientists also revealed new results showing that some deep-sea corals repeatedly invaded the shallow waters that house the most familiar coral species.

The findings represent the first known invasion from deep depths into shallow areas, revising many long-held assumptions about the evolution of marine organisms.

But experts warned that bottom trawling—the practice of dragging heavy nets across the sea floor—is causing widespread destruction of these ancient animals, with as many as half of the coral reefs found off the Norwegian coast showing damage from such fishing activities.

(Related: "Trawlers Destroying Deep-Sea Reefs, Scientists Say" [February 19, 2004].)

"We clearly need ways of managing deep-sea ecosystems, and maybe [putting] in areas that are closed to trawling if they contain a lot of vulnerable habitats," said TRACES project leader Murray Roberts, a marine biologist at the Scottish Association for Marine Science in Oban, Scotland.

Deep-Sea Gardens

Corals are often associated with shallow tropical seas, but two-thirds of the more than 5,000 known coral species are found in the cold, deep sea. There are 1,300 such coral species in the northeast Atlantic alone.

The corals can occur as small colonies or form large reefs and giant mounds up to 1,000 feet (300 meters) high.

These cold-water corals, which can build up over as much as two million years, have become a focus for scientists trying to understand both deep-sea evolution and climate history.

Many corals grow their skeletons like tree trunks, laying down growth rings that represent the ocean conditions at the time.

"Deep-sea corals have the potential to record such things as temperature changes and changes in ocean circulation," said Brendan Roark, a paleoceanographer at Stanford University in Palo Alto, California.

"We can look at changes in carbon dioxide as it moves from [the] atmosphere to water to the deep ocean, and all that is important to understand the past and future of climate change."

Invaders From the Deep

In a surprise find, one diverse group of corals originated in the deep sea and not in shallow waters as previously thought, scientists said.

Using DNA analysis, Alberto Lindner, a coral researcher at the University of São Paolo in Brazil, showed that stylasterids, or lace corals, evolved in deep waters before moving into shallow waters during at least three time periods in the past 30 million years.

Lace corals make up much of the Alaska Deep Sea Gardens off the Aleutian Islands. (See a Alaska map.)

The findings contradict earlier theories suggesting that corals and other marine animals all evolved in shallow waters before migrating into deeper habitats.

"It shows that deep-sea ecosystems are not isolated and static," Lindner said. "They are a source of diversity and evolutionary innovation."

Stephen Cairns is a research scientist at the Smithsonian Institution in Washington, D.C.

"I can remember for several decades when I was the only one working on deep-water Atlantic [stony] corals," Cairns said.

"so it is refreshing and gratifying to see these rather obscure animals in the limelight, and being used to help solve paleoclimatology and paleocurrent issues."

Ecosystems Connected

However, deep-sea corals are both difficult and costly to study because of their remote location.

Many of the reefs are found in the waters of developing countries, which cannot afford to organize expeditions to the ocean floor.

"We can't offer a single image of these corals from a developing country," said Lindner, the Brazilian scientist.

The best known cold-water ecosystems are in the North Atlantic, but these corals have also never been studied and compared across the ocean basin.

With the new program, researchers are planning exploratory cruises across the North Atlantic to study the environmental and ecological history of coral communities.

"We need to understand how one ecosystem is connected to the other," Roberts, the TRACES coordinator, said.

John Guinotte is a marine biogeographer at the Marine Conservation Biology Institute in Bellevue, Washington.

"Deep-sea corals are important sources of diversity for shallow-water regions of the ocean," Guinotte said.

"What this says to me is we should really question the wisdom of permitting destructive fishing gears, such as bottom trawling, in the deep sea where recovery of these ecosystems is incredibly slow, if not impossible, on human timescales."

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