A massive deep-sea coral die-off was discovered this week about 7 miles (11 kilometers) southwest of the source of the Gulf of Mexico oil spill, scientists announced Thursday.

Large communities of several types of bottom-dwelling coral were found covered with a dark substance at depths of about 4,600 feet (1,400 meters) near the damaged Deepwater Horizon wellhead, according to a scientific team on the National Oceanic and Atmospheric Administration (NOAA) ship Ronald H. Brown.

(Read about the Gulf oil spill in the October issue of National Geographic magazine.)

"The coral were either dead or dying, and in some cases they were simply exposed skeletons," said team member Timothy Shank of Woods Hole Oceanographic Institution.

"I've never seen that before. And when we tried to take samples of the coral, this black—I don't know how to describe it—black, fluffylike substance fell off of them."

"Smoking Cannon" Evidence for Gulf Oil Spill

About 90 percent of 40 large groups of severely damaged soft coral were discolored and either dead or dying, the researchers say. A colony of hard coral at another site about 1,300 feet (400 meters) away was also partially covered with a similar dark substance that's likely oil from the BP spill.

"Corals do die, but you don't see them die all at once," said cruise lead scientist Charles Fisher of Penn State University. "This ... indicates a recent catastrophic event," he told National Geographic News.

The circumstantial evidence is strong enough to be considered a "smoking gun" that the BP spill could have played a role in the coral deaths, Fisher said in a statement.

For one thing, the dead coral was found at 4,600 feet (1,400 meters), about the same depth as the now sealed wellhead, and currents at the time of the April 20 blowout would have carried the oil southwesterly, scientists say.

"The proximity of the site to the disaster, the depth of the site, the clear evidence of recent impact, and the uniqueness of the observations all suggest that the impact we have found is linked to the exposure of this community to either oil, dispersant, extremely depleted oxygen, or some combination of these or other water-borne effects resulting from the spill," Fisher said in a statement.

Scientists have predicted for months that the oil is not degrading and that the toxic ingredients may be having dire and unseen effects on the Gulf's marine life.

In August, for example, University of Florida (USF) oceanographer David Hollander discovered that deep-sea creatures showed a "strong toxic response" to Gulf water containing hydrocarbons, an ingredient of oil.

Hollander's USF colleague John Paul told National Geographic News Friday that the newly discovered coral die-off is more of a "smoking cannon."

"It doesn't surprise me," he said. "It could be the tip of the iceberg of all kinds of weird things we're going to see in the Gulf of Mexico in the next three to five years" due to the Gulf spill, Paul said.

Even so, both Fisher and Paul strongly caution that sediment and coral samples need to be tested in the lab to confirm a Gulf-spill origin.

Coral Graveyard a Surprise Discovery

The research cruise is the most recent leg of a four-year study of deepwater coral in the Gulf of Mexico (map), which are widespread in the region. (See coral pictures.)

Natural gas seeps attract microbes that result in rock formation, providing a hard surface for the coral to grow on. Over thousands of years, a diversity of corals have built communities at these depths, which are often difficult to access and study. (Read more about the Gulf of Mexico's natural seeps.)

In light of the Gulf oil spill, in 2010 the research team focused on finding oil-related impacts to Gulf coral. The dead coral—found in an area of about 50 by 130 feet (15 by 40 meters)—was spotted during the final dive of a three-week cruise. Previous expedition dives had revealed no visible damage to coral in other parts of the Gulf.

"We were hoping not to find anything," Woods Hole's Shank said.

Penn State's Fisher added, "We were looking for subtle changes. ... What we saw was not subtle."

A Lot of Work to Do in Gulf



Erik Cordes of Temple University is associated with the cruise but was not onboard at the time of the discovery.

"We are all saddened by this news, but it goes to show that we still have a lot of work to do," he said via email.

Cordes and colleagues plan to return to the Gulf with a submersible (learn more about the oil-detecting robots in the Gulf) in early December to further investigate the damaged coral.