Has Oil Fouled Up the Gulf's Filtering System?

A study examines the effects of the oil disaster on the water filtering sponges of the Gulf's reefs

05-03-2011 // Bob Serata
Barrel Sponge

They could be called the ‘Rodney Dangerfield’ of the Gulf, because they get “no respect.” Certainly none from the scientific community that studies “charismatic megafauna,” those large, lovable life forms like dolphins, pandas, bald eagles and fuzzy polar bears.

But in the cold-blooded, scaly, scratchy, sometimes slimy (it’s a protective layer) world of marine invertebrates, the sponge is an ancient hero of the seafloor.

Sponges are among our oldest multicellular evolutionary relatives. Fossil records of sponges date back at least 580 million years. When life on earth evolved from single- to multi-cellular forms, it was the sponge (phylum Porifera) that led the way.

Today, scientists consider the giant barrel sponge (Xestospongia muta) to be the longest-lived animal on the planet. One of these so-called “Redwoods of the Reef” was estimated to be more than 2,300 years old when it was discovered off the Caribbean island of Curaçao in 1997.

During a long-term study by Drs. Joseph Pawlik and Christopher Finelli, both of the University of North Carolina, Wilmington, barrel sponges were found living on Florida Keys reefs that were estimated to be 2,000 years old.

Like Brita, but Better

Sponges pull water through their bodies, filter out their food, and pump the filtered water back out to sea. Some sponges filter nutrients, cleansing the water so corals and other species that are distressed by the algae that thrive on these nutrients can enjoy a healthier habitat. Other sponges have been found to recycle dissolved carbon — taking carbon from the sea water and instead of growing, shedding newly formed cells that then become food for other reef inhabitants.

“Sponges provide ecosystem services,” said Dr. Felicia Coleman, director of Florida State University’s Coastal & Marine Laboratory in St. Teresa, Fla. “So if all along the Gulf they get plugged with oil and you lose that ability, an important filtering function is lost,” she said.

Barrel Sponge

Drs. Christopher Stallings and Christopher Koenig, both of FSU, are leading a study in Coleman’s lab to examine the effects of the Gulf oil disaster on shallow water coral- and sponge-dominated reefs.

Their work is part of a more extensive FSU-developed rapid response study entitled “Impact of Crude Oil on Coastal and Ocean Environments of the West Florida Shelf and Big Bend Region from the Shoreline to the Continental Shelf Edge” that involves 14 FSU scientists. Funding came from The Northern Gulf Institute to start data collection as soon as possible after BP’s Macondo well blew up and sent some 206 million gallons of Louisiana sweet crude into the Gulf of Mexico.

The Invisible Enemy

Coleman doesn’t expect to see oil-smothered sponges and corals in the shallow waters of the West Florida Shelf. Rather, she’s more worried about an invisible invasion that might affect invertebrates (e.g., sponges) and reef fish.

“In this region, I’ll be really surprised if we see crude oil. I’d expect to see dispersed oil [i.e., spread by the chemical dispersant Corexit]” she said. “The chemists are saying you can have it, but you can’t see it. You can’t feel it, and it’s not until you start doing the chemical analyses that you realize that you’ve got dispersed oil,” Coleman continued.

The FSU scientists studying sponges, corals, and their reef-dwelling brethren are looking into the entire biological community, documenting distribution and abundance patterns, species richness, composition and size structure to create baselines that will allow communities and individual organisms to be tracked over time.

One of their goals is to detect linkages between geologic, geographic and biological habitat features of shallow sponge and soft coral reefs by gathering some baseline data or, at least, data which can be used to compare “now” versus “later.”

These findings might have implications as reference data for the Natural Resource Damage Assessment (NRDA) process, though this study is not a designated part of the NRDA. According to the NOAA NRDA website: “Although the concept of assessing injuries may sound simple, understanding complex ecosystems, the services these ecosystems provide, and the injuries caused by oil and hazardous substances takes time—often years.”

Problem is, how do you fix (i.e., “restore” or “compensate for injury” according to NOAA) a Corexit-poisoned sponge? You can’t just wring it out like you’re dealing with dishwashing detergent – that will surely kill the sponge. And what’s an underwater filtering system worth? Floridians have been arguing about water quality issues (and, more recently, the newer science of ecosystem services) since there have been Floridians. Even more bewildering, ask yourself this: what’s the dollar value of a living reef sponge?

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