Attack of the seaweed

It seemed a good year was shaping up for South Carolina shrimpers with fuel prices down from last season and plentiful rain to carry shrimp out of their nursery grounds along the shore. But then came the seaweed invasion.

Blooms of two types of invasive seaweed tangled shrimpers' nets for six weeks from May to mid-June, costing them time, fuel, labor and much of their catch.

"I've been doing this since 1970 and I've never seen it before in my life — nothing like this," said Wayne Magwood, a Mount Pleasant shrimper who is president of the South Carolina Shrimpers Association.

Conditions this spring were ideal for blooms of seaweed known as polysiphonia and gracilaria.

Polysiphonia, native to the Mediterranean, has been found in the Southeast for decades but seldom causes problems along the South Carolina coast, said Erik Sotka, an assistant professor of biology at the College of Charleston's Grice Marine Laboratory.

A more recent arrival, gracilaria, native to waters near Japan, is now found in South Carolina's estuaries as well as in the Savannah River. Sotka is studying the impact of the plant on the tidal food web.

Shrimp nets could not trawl the bottom because they were tangled with the seaweed.

"There seemed to be more than in the last good many years," said Richard Baldwin, who shrimps out of St. Helena Island.

Magwood said his catch was down about 80 percent because the seaweed caused the nets to trawl several feet off the ocean floor, above where the shrimp are found.

"The shrimp were there but we couldn't make any money because the shrimp weren't going into the net," he said.

Mel Bell, the director of the Office of Fisheries for the state Department of Natural Resources, said spring conditions were ideal for a bloom.

"As the water warms up in the spring, it hits a favorable optimal temperature for a bloom. In some years, if it warms up too quickly, you blow right through that. But this year things lined up for it," he said.

As weather grew warmer, the bloom faded.

Sotka said there isn't a lot of natural seaweed along the South Carolina and Georgia coasts because of the tidal range of 6 feet to 7 feet.

"Seaweeds don't like a lot of silty water on top of them," he said, adding that gracilaria, first noted in the area about 10 years ago, is different.

"It has been termed the perfect invasive because you can bury it for days and bring it out of the sediment and it does fine," Sotka said. "It's an incredibly tolerant species, which means it can invade a lot of different areas."

The seaweed might have arrived in ship ballast or as spores in transplanted oysters, he said.

The state's 400 licensed shrimp boats are expected to harvest nearly 2 million pounds of shrimp this year, although that could be lower because of the blooms. The good news is that fuel, which reached $4 a gallon last season, is now half that.

Baldwin said the biggest challenge for shrimpers isn't seaweed, but cheap foreign imports.

"That's the thing that's going to put the shrimpers out of business," he said.

"Hopefully things are going to get better," Magwood added. "It's always been a battle with shrimping. You always try to think about the good days and not the bad days."