FLORIDA KEYS -- Sponges are beginning to outcompete coral along the Florida Keys reefs, according to several scientists.
"Reefs in Florida and the Caribbean are shifting from being coral dominated systems to being more sponge and algae dominated systems," Melissa DeBiasse concluded in last month's issue of Molecular Ecology.
The Louisiana State University researcher noted the transition of reefs away from coral while investigating the genetic structure of sponges and how it relates to their population. She visited reefs from Key Largo to the Dry Tortugas as part of her study.
Joe Pawlik, a biologist at University of North Carolina-Wilmington, has been tracking the growth of Florida Keys reef sponges since 2000 and has witnessed the change. The deeper the reef, the more likely it will be overcome with sponges, he says.
Sponge volume on Conch Reef, just off Plantation Key, has more than doubled in the last 14 years, he said.
Neils Lindquist, a professor of marine science at University of North Carolina's Morehead City laboratory, agrees that sponges are reshaping the reefs.
"Coral cover has declined and animals and plants are competing for space," Lindquist told the Free Press last week.
The sponge doesn't suffer from predation to the same degree as coral and is better at fighting off disease, he said.
Consequently, scientists need to better understand the impact of sponges as they begin to dominate the reefs, Lindquist said.
Sponges cycle nutrients, provide habitat and help keep coral rock cemented together. Acting as filter feeders, sponges can pump up to 100,000 times their volume in a day, Lindquist said. But as they eat up much of the organic compounds floating around the reefs, they, in turn, release ammonium nitrate into the water.
"This puts a hamper on the diversity of fish," Lindquist said.
Lindquist says alternative ways to manage the growing population of reef sponges must be pursued.