A four-year search for toxic Pfiesteria in Maryland waters has uncovered evidence that several other varieties of harmful algae, often fueled by pollution, may be seriously damaging bay life.
For years, scientists thought that the Chesapeake Bay and Maryland's coastal bays were mostly free from the harmful algae blooms that plague seriously polluted waters around the world - and are increasingly seen in state waters at this time of year.
But after Pfiesteria killed fish and sickened people on some Eastern Shore rivers in 1997, the State Department of Natural Resources fielded teams of biologists to look for signs of the toxic cell.
They found not only widespread traces of Pfiesteria, but also two previously unknown algae varieties capable of killing bay creatures. And they discovered that some familiar algae blooms are not as innocuous as once thought.
There is evidence that these algae can kill underwater grasses, prevent oyster larvae from hatching, contaminate shellfish and fray the web of bay life.
Unlike Pfiesteria, no other harmful algae found in state waters have been linked to human illnesses in the United States. But experts say the damage they are doing to Maryland's waterside way of life may be more serious in the long run.
Until Pfiesteria got the state's attention, "we really didn't recognize any other harmful algae blooms in the bay, even though we knew up and down the coast they were having problems," said Robert Magnien, director of the Department of Natural Resource's tidewater ecosystems division.
"Over the last few years, a lot of things have come to light," Magnien said. "We're discovering we're not as free of some of these problems as we might have thought."
Pfiesteria has been quiet for three years, with no major outbreaks and no rivers closed to protect the public's health. Tests by DNR biologists show low levels in lots of places, and Marylanders have learned to live with that.
But this summer, as in past years, at least three other harmful algae varieties are at work:
A brown tide organism that has devastated commercially valuable fisheries from Rhode Island to New Jersey was discovered in Maryland's coastal bays in 1999 and bloomed heavily in two places last year. At the end of last month, researchers were tracking two blooms even denser than last year's in salty Newport Bay and a portion of Chincoteague Bay.
A strain of mahogany tide that has been here for decades was discovered last year to be capable of producing a toxin that poisons oysters and other shellfish. A huge mahogany tide in the Choptank River and elsewhere was the largest recorded in 20 years. Smaller blooms appeared in portions of the river in the last week of June.
Blue-green algae, a freshwater species that can kill dogs, cattle and other domestic animals if they lap up tainted water, were blooming last month on the Potomac and Sassafras rivers.
A fourth organism, discovered at a Delaware fish kill last year, was also found at low levels in Maryland waters. Chattonella verruculosa has killed fish in Japan and produces the same toxin that sickens beach-goers during red tides in the Gulf of Mexico.
These blooms fit a worldwide pattern; reports of toxic algae outbreaks have doubled in the past 30 years. The causes aren't clear, but in many cases scientists suspect high levels of pollution from nitrogen or phosphorus - potent plant nutrients that can cause explosive algae growth.
Experts estimate that Chesapeake Bay nutrient levels are about seven times higher than they were at the time of European settlement. Nutrient levels in the coastal bays are also rising as the shorelines get more developed.
The state now routinely monitors for Pfiesteria and other harmful algae at 58 sites in the Chesapeake, its tributaries and the coastal bays. Each year, the DNR's rapid response team - created in the wake of the 1997 Pfiesteria outbreaks - takes another 100 to 300 samples in response to reports of sick or dying fish.
This year's monitoring has turned up low levels of Pfiesteria at three sites on the Pocomoke and Chicamicomico rivers and on Fishing Bay, but no fish kills have been reported.
"Overall, bay waters are still very safe for fishing and recreation, just as safe as they were 10 years ago," Magnien said. "There's very little to worry about in terms of human health problems."
But the toxic blooms could have "subtle and not-so-subtle impacts" on commercially valuable bay creatures like blue crabs and oysters, Magnien said. "It could be that you're losing 20 or 30 percent of the population, and you'd never be able to absolutely document it, unless you were out there looking extremely carefully day to day."
For information on harmful algae blooms in Maryland, check DNR's Internet site at www.dnr.state.md.us/bay/hab/index.html.
Mahogany tide algae
It's an unwelcome sign of spring in parts of Chesapeake Bay country: When heavy rains fall, the warming, brackish water turns murky red-brown with an explosion of algae.