Coral reefs, Cliona delitrix Andia Chaves-Fonnegra NSU Nova Southeastern University Oceanographic Center
It's such a vibrant orange that divers think it's part of South Florida's colorful coral reefs.
But it's a destructive sponge that for the past decade has been spreading and threatening corals, which already are deteriorating around Florida and the Caribbean.
"It's a beautiful orange sponge, but it is an excavating sponge, able to bore inside the coral," said Andia Chaves-Fonnegra, a PhD student at the Nova Southeastern University Oceanographic Center in Dania Beach, who is heading up a research project into the scourge.
Normally, reefs have natural defenses. Yet, the current mortality rate for local reefs has been high because of seaborne diseases and warmer waters. That has given the orange sponge --which can reproduce three to five times per year – more room to grow, said Chaves-Fonnegra, 34, of Delray Beach.
"The sponge is not what we call an invasive species, but it is a strong competitor, specifically with coral," she said.
For now, the sponge's spread is being monitored. But to stem its growth, Chaves-Fonnegra said ocean pollution should be reduced, as it is nurtured by sewage and other materials.
Often crusty and pock-marked, sea sponges are classified as animals, even though they don't have circulatory, digestive or nervous systems. They survive on the power of water flowing through their bodies to obtain food and oxygen.
Chaves-Fonnegra, with help from others at NSU, recently discovered the orange sponge, formally called "Cliona delitrix," is proliferating because its larvae attach to dead parts of corals. That aspect of its attack had gone undetected, even though it was widely known the sponge could be deadly.
When it leaches onto corals, it takes up space where new corals – made up of colonies of tiny animals that secrete calcium carbonate – would otherwise start to grow.
"The sponge makes holes inside the coral and dissolves the calcium carbonate," she said. "It erodes the coral's three-dimensional structure."
Of some consolation, the orange sponge has not grown as fast in South Florida as in other regions, thanks to high levels of algae and ocean sediments, said Chaves-Fonnegra. She said algae and sediments form "carpets" of sorts, making it difficult for the sponge to get into the coral.
Even without the threat of killer sponges, coral reefs are under constant attack from parasites and predatory fish, such as the lionfish.
Chaves-Fonnegra has been diving into waters around the Caribbean to monitor the sponge and is writing her doctorate dissertation on it.
Her work is important toward ensuring the coral reefs remain healthy, said Joe Lopez, an associate professor at the NSU Oceanographic Center.
"We're trying to understand how the sponge reproduces and its overall pattern," he said.
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