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Pinpoint accuracy

Keys marker does double duty

Keys marker does double duty

For those who have wondered how precise their GPS readings are, the Florida Keys National Marine Sanctuary has installed a buoy off Key Largo that can be used as a reference point to check a unit’s accuracy.

Located at 25 degrees, 00 minutes, 38 seconds north and 80 degrees, 22 minutes, 22 seconds west, the buoy is attached to an underwater geodetic marker, the nation’s first. It marks the place where a 400-foot freighter went aground on Molasses Reef Aug. 4, 1984.

Wellwood, a Cyprus-flagged ship, pulverized 16,683 square feet of the coral reef in that mishap. The geodetic marker, affixed to the bottom June 17, will be used as a precise reference point for scientists to monitor the reef’s recovery and repopulation with coral and other marine species.

The buoy has two purposes. It reminds boaters to check the accuracy of their electronic navigation gear when they are in the Keys so that they don’t plough into reefs, and marks the reef so recreational divers can see the results of a $6.3 million restoration paid for by Wellwood’s owners and managers.

“It isn’t going to tell you to the centimeter where you are, but it is going to tell you within feet whether your instrument is working,” says reef biologist Harold Hudson, who led the restoration effort.

While the buoy may be off location by a few feet, the geodetic marker 20 feet below is exactly where it’s supposed to be. The stainless steel marker is permanent and “indestructible,” fixed to the coral with four 12-inch bolts. “You could moor the Queen Mary to that thing,” he says.

Scientists can slip a 4-foot-diameter fiberglass compass rose over the marker to measure distances and angles from the marker to points on the reef so that they can map those points and monitor them for new coral growth.

“As long as you have that [mapping data] safeguarded, you could go out there 100 years from now and find those spots,” he says.

The primary reef rebuilding process involved designing precast concrete modules riddled with caves, overhangs and crevices and placing them on the part of the reef that the Wellwood literally flattened. The modules mimic a coral reef that promotes the growth of algae, then a hard coralline algae coating that cements loose coral and shells together, and over many years live coral and other marine organisms.

Completed in 2003, the restoration is showing results: sea fans, plumes and whips — “Hundreds of them,” Hudson says — and new populations of fish, shrimp and lobster. “We’re seeing some things at the restoration site that make us feel pretty darned good,” he says.

With luck, the reef could be close to what it was before the grounding within 50 years, Hudson says. Without the artificial rebuilding to create a foundation, natural restoration would take eons.