Brown tide in bay not harmful to people

Water experts say risk is posed to animals, plants

May 24, 2002|By Heather Dewar | Heather Dewar,SUN STAFF

A brown tide that has been blooming for more than two weeks in Isle of Wight Bay near Ocean City could be harmful to bay life, but not to people, state water quality experts say.

Coffee-colored water appeared early this month in the St. Martin River and in Herring and Turville creeks, near Isle of Pines on the bay's western shore, and in Assawoman Bay. It also turned up south of the Ocean City inlet in Chincoteague Bay but has since faded in that area, state officials said.

Tests by the Maryland Department of Natural Resources traced the dark stain to a harmful algae, Aureococcus anophagefferens, first discovered in New England in 1985.

"This is the first time we've seen major blooms in the northern bays," although brown tide has been seen before off Assateague Island, said David Goshorn, chief of DNR's living resource assessment program.

Laboratory tests show the brown tide is dense enough to cause problems for clams, scallops, juvenile fish and underwater grasses. The agency is awaiting confirmation of initial tests showing algae counts of more than 700,000 cells per liter of water -- thick enough to kill some bay life, DNR biologists said.

Aureococcus is not toxic to people and doesn't taint shellfish, which remain safe to eat, the biologists said.

Two other harmful algae types were at low levels in the northern bays early this month. One microorganism, Dinophysis acuminata, can sicken people who eat tainted shellfish, and forced the temporary closure of some Potomac River oyster beds in February. In the coastal bays, it has been found only in places that are already off-limits to shellfish harvesting because of pollution, Goshorn said.

The other variety, Prorocentrum minimum, causes a reddish-brown discoloration called mahogany tide. DNR natural resources planner Peter Tango said that in rare cases, the algae can be toxic and one Chesapeake Bay sample from the 1990s tested positive for potential toxicity. However, mahogany tide levels were relatively low in early May and had fallen lower by mid-May, DNR biologists said.

Scientists aren't sure what causes the blooms. But Robert Magnien, director of DNR's tidewater ecosystems division, said there is evidence linking brown tide to high levels of nutrients, which may come from sewage, animal waste or decomposing plants. The St. Martin River, Herring Creek, Turville Creek and the nearby waters of Isle of Wight Bay have some of the coastal bays' highest nutrient levels, DNR tests show.

"People should be concerned about that, because it's an indication the bays are not as healthy as they could be," Goshorn said. "As far as swimming, jet-skiing or fishing and eating what you catch, there should be no concern there."

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