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Life & Death of a Coral Reef

Geologist Gene Shinn calls it his "Stupid Rock Trick."

What it shows, however, might explain the demise of Florida's coral reefs.

Shinn pours water onto a slab of limestone rock, the same type of rock that underlies most of the Keys. Almost instantly, the water pours out the bottom of the slab.

"We're talking about some of the most permeable rock in the world," Shinn says.

In an experiment begun last year, Shinn said, he is finding that the porous rock beneath the Keys is allowing sewage waste water from Keys communities to seep out to the reefs.

His findings, presented last week to a conference of some of the world's most respected reef experts, provide perhaps the strongest evidence to date of why the once-rich coral reefs of the Florida Keys are dying.

The conference of some 125 experts was the first attempt to assess the health and the future of the world's reefs _ home to some of the world's most important seafood stocks and a popular vacation destination for millions of people who want to view the exotic animal species that inhabit them.

The experts agreed that many of the Earth's reef systems are in trouble, particularly those near large urban areas. Some, like the Keys, are succumbing to pollution or strangling on silt being washed down from deforested or overcultivated upland areas.

Much of the experts' attention was drawn to the Keys, which begin just across Biscayne Bay from the University of Miami's Rosenstiel School of Marine and Atmospheric Science, site of the meeting. The Keys reefs, next to densely populated South Florida, are declining.

Shinn, with the U.S. Geological Survey group, based in St. Petersburg, presented preliminary information he and colleagues have gathered from wells drilled beneath the shallow waters off Key Largo in the upper Keys.

The information indicates that nutrients found in the waste water from the Keys' sewage treatment plants are seeping horizontally from beneath the island to the giant stands of coral.

The nutrients then feed algae, which grow, cover and eventually destroy the coral. Coral normally thrives in a low-nutrient environment.

"There's a huge area out there where the nutrient water can pump in and out of the rock," Shinn told the gathering.

Scientists long have suspected that nutrients were feeding algae blooms in the Keys reefs, but they had been unable to explain how.

Years of sampling and testing the salt water, for example, showed relatively little nutrient buildup in the water surrounding the reefs. But the porous rock that forms and underlies the Keys provides a natural conduit for the water from sewage plants and septic tanks.

There are more than 1,000 state-approved sewage treatment plants in the Keys today, Shinn said.

And after removing sewage solids from the waste water, most of those plants simply pump the water into holes typically drilled no deeper than 30 to 40 feet, Shinn said.

Looking for evidence of sub-surface nutrient movement, Shinn's researchers last year began drilling two strings of specially encased wells from heavily populated Key Largo eastward across Hawk Channel and through the Grecian Rocks, a reef area long famous with the thousands of dive enthusiasts who visit the Keys annually.

"While drilling these wells we noticed that there's intense tidal pumping," Shinn said. "We often joked that we could make electricity by putting propellers on those things (the wells)."

Elevated levels of nitrates and phosphates were found in well-water samples taken closer to shore, but Shinn isn't sure whether those nutrients can be ascribed to sewage plants or to a nearby golf course.

But the readings soared for ammonia, another nutrient, which was found in high concentrations in the water beneath the Grecian Rocks area.

"We've come to the conclusion that where these rocks are exposed, they're literally breathing water every day," Shinn said. "There is this pumping, and probably a lot of leakage. And one of the places where it can leak is directly through the reef, because that's where most of the permeability is."

Anyone familiar with the Keys' reefs knows that Shinn's work is more than an academic exercise: The reefs have been dying for years. Shinn offered the proof.

For more than 30 years _ since 1961 _ Shinn has photographed the same coral rock each year.

He displayed those photos last week. The star coral outcropping was largely bare in 1961, thanks to a hurricane that stripped most of the softer corals away. Within a few years, though, staghorn coral appeared. Then elkhorn coral took hold. They all grew to a lush profusion until 1976, when they began to take on a stunted look.

They declined each year thereafter. Today, the sand surrounding the rock is bare and was so before Hurricane Andrew.

Shinn and his colleagues began their research into the decline of the Keys reefs about a year ago. They have operated on a financial shoestring. They want to expand their geologic research south toward Key Largo and west into Florida Bay, but any future work hinges on a five-year funding proposal now being considered in Congress.

For now, they have twice sampled their existing wells and plan to draw two more sample sets before year's end. That is all the money they have.

"The reason I'm doing this is because I've been to several meetings like this in the last few years, and I listen to a lot of people talk about what they're going to do," Shinn said. "You seldom hear much about what has been done."

As for the experts, they have decided they will meet again in 1996 at the Smithsonian Institution's reef research station in Panama.

They already have a name for their convocation: The International Year of the Reef.