Associated Press

Early on in the BP oil spill, I interviewed some marine biologists who had spent nearly a decade charting a series of deepwater coral reefs in the Gulf of Mexico.

Concern ran high that drifting plumes of dissolved oil particles and of chemical dispersant, which was being applied directly to the gushing well to break up oil before it reached the surface, would harm coral communities in near the spill site.

A few preliminary surveys in the aftermath of the spill found no clear evidence of harm, leading to some early optimism that the deepwater coral had perhaps dodged an ecological bullet.

But this week, scientists piloted a submersible robot to the seafloor seven miles southwest of the well and found dozens of recently dead and dying coral communities. The site was in the direct vicinity of where large plumes of dispersed oil were discovered drifting through the deep ocean last spring in the early weeks after the spill.

Charles Fisher, a marine biologist from Penn State who is the chief scientist on the gulf expedition, told me he had expected to see some subtle effects from the oil. Instead, he found an ecosystem in collapse.

“I have seen many individual dead coral colonies over the years, but I’ve never seen a site full of dead and dying coral colonies,” he said.

Roughly 90 percent of corals at one site he surveyed were dead or dying and covered in a brown substance that he suspects was not oil but “gooey, rotting coral tissue.”

Further testing is necessary to determine exactly what killed the coral, but Dr. Fisher said the circumstantial evidence linking the die-off to the oil spill was overwhelming and represented “a smoking gun.”

“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,” Dr. Fisher wrote in a statement released Friday afternoon by Penn State.

Whether more damaged coral exists near BP’s now-capped well remains to be seen. According to Dr. Fisher, he and a fellow scientist have identified a series of 25 sites within 15 miles of the wellhead that may host undiscovered coral communities. The site of the coral die-off discovered this week was the first of the 25 sites surveyed.

Another research cruise is planned for December to examine more of these target sites.