MIAMI — A MYSTERIOUS patch of algae is raising concerns about the future of North America's only bank barrier reef. The reef, which stretches more than 200 miles around the Florida Keys, is already threatened by local pollution, such as private septic tanks, fertilizers from golf courses, and wastewater runoff. But this particular patch of algae is troubling because it is so large and located much farther offshore, about four miles east of Key Largo.
No one knows what caused the algae to bloom. But some scientists suspect that a labyrinth of underground rivers and groundwater channels is carrying pollutants to the reef - not just from the Keys but from throughout south Florida. That does not bode well for the fragile coral.
``It's irreversible damage,'' says Brian Lapointe, director of marine conservation for the Florida Keys Land and Sea Trust, a privately supported conservation group.
This is perhaps the first time a large patch of algae has bloomed on the reef. ``It's an event we haven't seen,'' says John Halas, a biologist at the Key Largo National Marine Sanctuary. ``We are suspecting there might be some groundwater intrusion.''
The idea that polluted groundwater is reaching the reef that far offshore has set off alarm bells for a local environmental group.
``The unspoken fear is that it's nutrients from agricultural sources,'' says DeeVon Quirolo, administrator of Reef Relief based in Key West. ``The scientists don't want to say that because they can't prove it. But where else could it be coming from?''
Scientists discovered the 75- by 100-meter patch of algae last August. Long tufts of the algae, like red, green, and brown cotton candy, were choking the soft coral structures like sea fans and sea whips. When Drs. Halas and Lapointe returned in February, the algae patch was still there - not any bigger but not any smaller than it was before.
``It hadn't spread from what we could see,'' Dr. Halas says. ``I don't know at this point what we can do about it except monitor it.''
Lapointe is not hopeful about the reef's future: ``There's nothing that can be done. There's too little reef and too many people.''
But Reef Relief is preparing for a political fight with the state's agricultural interests over limits on pesticide use. ``The battle lines have not been formed,'' says Ms. Quirolo, but a showdown is inevitable.