Officials keeping tabs on waterways

Waters near Ocean City have elevated amounts

July 27, 2000|By Chris Guy | Chris Guy,SUN STAFF

After monitoring the first bloom of brown tide in Maryland's coastal bays last month, state environmental officials are keeping close tabs on Chincoteague Bay and other shallow waterways near Ocean City where the prolific algae appeared in dense concentrations last month.

The question, they say, is whether Aureococcus anophagefferens, as it's known to researchers, will return in numbers large enough to threaten shellfish, eelgrass and other underwater vegetation when water temperatures begin to dip in mid- to late-September.

"It's a really one of those warning flags that concerns us," said David Blazer, executive director of the Maryland Coastal Bays Program. "It's relatively new, or at least we've only been aware of it for a couple of years. We saw the elevated numbers in June, but we're not sure what, if any, damage there was."

Once thought to be present only in waters from Rhode Island to New Jersey, limited primarily by its preference for cooler water temperatures, moderate levels of the algae - 100,000 to 200,000 cells per milliliter of water - were detected in Delaware coastal bays two years ago.

A 15-station monitoring effort initiated last year by the Maryland Department of Natural Resources turned up similar results.

In late May and early June, with water temperatures around 68 degrees, the optimum for the organism, densities reached 500,000 to nearly 900,000 cells per milliliter of water at some testing sites, causing the tell-tale discoloration of water known as brown or red tide. Scientists have suspended sampling until September, when the stations will be checked once every two weeks.

Unlike Pfiesteria piscicida, the deadly microbe that has been linked to fish kills and human health problems in Chesapeake Bay tributaries, the algae appears harmless to humans, as well as to fish and other creatures that can simply swim away from heavy concentrations.

"Part of the good news is that there's no evidence that it causes problems for people," said David Goshorn, a DNR biologist. "We don't want people thinking this is another pfiesteria."

Clams and other shellfish, however, could be affected because brown or red tide prevents bivalves from feeding on more nutritious forms of algae. Scientists haven't determined whether the algae produces toxins harmful to shellfish, as similar strains have.

"One of our concerns is that there could be damage to worms, snails and other organisms that we might not necessarily catch or eat that are all vital parts of the food chain," Blazer said.

Eelgrass and other submerged aquatic vegetation (SAVs) that are vital to sustaining all manner of marine life could be harmed because heavy concentrations of the algae blocks out sunlight, said Goshorn.

"We don't know if any commercially significant shellfish have been harmed, but some preliminary photo evidence seems to show a slight decline in SAVs," Goshorn said. Researchers think it's possible the algae has been present in low levels in Maryland waters for years without detection because there was never reason to test for it, Goshorn said. Reduced rainfall, elevated salinity and high levels of nutrients are thought to promote the development of blooms, he said.

Scientists admit they are somewhat baffled because higher concentrations of the organism have been found in Chincoteague Bay, which is wider and larger than Maryland's upper bays and is generally assumed to have better water quality.

"It's very possible that all this is perfectly natural, and we're just now finding out about it," Goshorn said. "The question is whether this is something we are doing that has encouraged these blooms. There is really so little known about what causes the organism to bloom."

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