Moving Urchins to Save Reefs, News-Press.com, 08/27/06
By Kevin Lollar
Source: The News Press
TAVERNIER — Moving day at Conch Reef recently was a prickly business, and the movers all wore gloves.
Scientists and volunteers spent the day 5 miles offshore rounding up about 500 long-spined sea urchins in a shallow rubble zone and moving them to deeper water on the coral reef.
With the height of hurricane season approaching, the idea was that the urchins (often called Diadema for their scientific name Diadema antillarum) will be safer on a reef in deep water than in rubble in shallow water.
"When the wind blows 25 or 30 knots, the rubble starts rolling around and kills everything," said tropical fish collector Ken Nedimyer. "After Wilma, there was not a thing living in the rubble area, nothing. It's coming back to life, but it'll get creamed again."
Nedimyer and Martin Moe, a Mote Marine Laboratory adjunct scientist, conducted a Diadema-transfer experiment in 2002 and 2003 that showed moving the urchins increases their chance for survival.
Now Moe and Nedimyer, with help from the Florida Keys National Marine Sanctuary, The Nature Conservancy, the Florida Institute of Oceanography and a handful of volunteers, are out to move as many long-spined sea urchins to safety as possible.
But why bother? After all, many divers consider the urchins, whose sharp spines are coated with a mildly toxic mucous, a sometimes painful nuisance.
Simply put, moving Diadema will help save the Keys' coral reefs.
Long-spined sea urchins are voracious grazers of macroalgae, and a healthy population of urchins keeps algae in check.
Diadema once packed reefs throughout the Caribbean region. Researchers documented densities of at least three to six individuals per square meter, and one study reports that 20 per square meter were not uncommon.
But in January 1983, huge numbers of Diadema started dying in Panama. The mysterious epidemic quickly spread to Colombia, Costa Rica, the Cayman Islands, Jamaica and the Yucatan Peninsula. By August 1983, long-spined sea urchins were dying throughout the Keys and the Bahamas.
Within 14 months of its onset, the epidemic wiped out 98 percent of the Caribbean region's Diadema.
As is often the case when an essential piece of an ecosystem disappears, bad things soon happened.
"I was happy when they all died," Nedimyer said. "They were a plague on the reef. They'd poke you everywhere you'd go.
"But a few years after they died, some of my favorite habitats were overgrown with algae. The whole system is keyed to one grazer."
Without the urchins, algae took over Caribbean reefs, not only smothering live corals but also inhibiting settlement of coral larvae and, thus, the creation of new coral colonies.
Excess algae and lack of new colonies became just one more threat to coral reef systems that are already being destroyed by disease, human activity, hurricanes and global warming.
Although Diadema populations are growing in some areas of the Caribbean, Keys populations are still down.
"There are a lot of possible reasons for that, but no one has tied it down with scientific certitude," Moe said. "For one thing, the Gulf Stream is a barrier to larval dispersal. Also, the Diadema that are here are scattered, and when they're spawning, they have to be within a meter of each other for their eggs and sperm to get together."
Another possibility is a Catch-22 situation: Predators that eat juvenile urchins live in macroalgae covering the reef. As long as the algae are present, juvenile urchins have difficulty surviving to reproductive age.
But without a healthy population of Diadema, algae will remain.
Because so few long-spined sea urchins are left in the Keys, saving as many as possible is important for the health of the reef.
The process is simple: Divers swim around a rubble zone, in 5 to 10 feet of water, putting urchins in landing nets and transferring them to buckets aboard a boat for the trip to the reef half a mile away.
Divers then take the urchins to the reef 25 or more feet below, release them and wait until they scoot into a hiding place so predators such as triggerfish, jacks, wrasses and grunts won't pick them off.
"This is good habitat with holes where predators can't get them," said diver Jon Fajans, a research associate. "There are going to be losses. There are predators, and we can't protect all of them. I just hope we can put out enough that some survive."
Keys reefs, and reefs throughout the Caribbean, are in critical condition, and the lack of long-spined sea urchins is a big part of the problem.
So scientists and volunteers in the Keys will continue to transplant urchins until a hurricane or tropical storm wrecks the rubble zones.
"It's time to do something, and this is something we can do," Nedimyer said. "Urchins are part of the equation. You can do everything else right, but without the urchins, it doesn't matter."