Invasive red algae causes snarls for Lowcountry shrimpers

June 8, 2009 

Biologists are monitoring red algae that has popped up around the Lowcountry, including in Beaufort County, and will be checking its possible spread to other parts of the South Carolina coast.

The seaweed, known as gracilaria, is growing quickly in the Charleston Harbor, said David Whitaker, a biologist with the S.C. Department of Natural Resources.

Fishermen traveling the coast have heard that shrimping nets have been tangled in and destroyed by the invasive plant.

"It's pretty bad from Charleston to Rockville," said Donald Jordan of Georgetown County, who owns the shrimp boat, Kelly Ann. "From Charleston on south is where it seems to be worse. I heard it was tearing some nets up."

The plant isn't causing significant problems in the Beaufort County area, two shrimpers of St. Helena Sound said.

Richard Baldwin of Colleton County said there doesn't seem to be as much of the plant around Hunting Island, for example, as there is farther north around Edisto Island.

"Some years it's worse than others," he said. "This year, it doesn't seem to be as bad."

Steve Kerchner, who also catches shrimp in St. Helena Sound, said the plant is posing him no significant problems so far this year.

"Later on it may be," he said. "But right now, it's not."

Gracilaria first showed up in South Carolina five to seven years ago, said Erik Sotka, an assistant professor at the College of Charleston.

Biologists aren't sure how it got here, but it might have come from Japan on ships or oyster shells, Sotka said.

Sotka said colleagues will also test for the algae in Beaufort County this summer. Results should be available in the fall.

The plant is not a threat to human health, but it could affect marine life by disturbing mud flats and pulling oxygen from the water, Sotka said.

"Food webs might be pretty profoundly affected by the smothering this alga represents," Sotka said.

The seaweed is a drifting plant, but can be destroyed if fishermen bring it on board and then leave it on land. The plant will continue to grow if it is returned to the water after being removed from the nets.

The plant survives in salt and brackish water and in cold and hot weather.

"It's hard to predict what will happen," Sotka said. "This year, we're having more complaints and on a broader geographic range. We're concerned about the impact that it is having on the shrimpers and the impact on the estuaries."

The commercial shrimp fishing season in South Carolina opened in May and closes in January.

Meanwhile, another unidentified, invasive red seaweed has been seen in Charleston Harbor, Sotka said. The algae is also growing in Charleston Harbor, but has not been seen in other places, he said.

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