05 - Algae in Chesapeake Bay



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The Chesapeake Bay is subject to algae bloom from early to late summer. All are harmful to aquatic life in some manner. some have been linked to harmful effects in humans as well. Covered are four types of algae that are not known to cause disease in humans - Mahogany Tide - Brown Tide - Chattonella verruculosa - Blue-green algae




This is a transcription of an article appearing in the July 8th, 2001 edition of the Sunday Sun.

Mahogany Tide - Prorocentrum minimum

It' s an unwelcome sign of spring in parts of Chesapeake Bay country. When heavy rains fail, the warming, brackish water turns murky red-brown with an explosion of algae.

For decades, these mahogany tides were thought to be relatively harmless. But scientists now suspect the algae blooms of causing die-offs of fish and shellfish and loss of habitat. (editor: fish die-offs cause paddling the bay at these times to stink, literally)

The organism that causes mahogany tides, Prorocentrum minimum, is so widespread that blooms happen somewhere in the bay almost evert spring, and can continue into the summer. So far this year, state biologists have found Mahogany tides in the lower Potomac River, where they used up so much oxygen that some fish suffocated, and near the mouth of the West River. At the end of June, scientists were tracking small blooms in the Choptank River.

Last year, the biggest mahogany tides in 20 years appeared on the Choptank, Patuxent and Potomac rivers and along the Western Shore. At the University of Maryland's Horn Point Laboratory, mature oysters' production of young dropped tenfold when exposes to Prorocentrum in water from the Choptank. A hatchery on the Patuxent had similar problems.

"it certainly is suspicious," said Donald Meritt, who manages the Horn Point hatchery. "But I cannot tell you unequivocally that it was due to Prorocentrum."

In some areas where the bloom was worst, there was a big die-off in underwater grasses, which shelter crabs, young fish and other bay creatures. But there is no proof that Prorocentrum is to blame.

Some strains of the organism occasionally produce a toxin that can taint shellfish, which can cause liver damage in humans who eat them. Prorocentrum has caused deaths in Japan. Though no cases of shellfish poisoning have been reported in the United State, some laboratory tests on algae taken from the Choptank River indicate that they might be toxic to shellfish. "It was thought to be just a nuisance bloom in the bay." the DNR's (editor: Department of Natural Resources) Robert Magnien said of the mahogany tide. "But the more we look at it, the more questions we have."

Brown Tide - Aureococcus anophagefferens

A potential killer of shellfish and sea grasses has recently been discovered in Maryland's coastal bays: brown tide. Until 1998, the organism that stains shallow bays the color of milky coffee, Aureococcus anophagefferens, had never been found south of Barnegat Bay, N.J. But then it turned up in low levels in Assawoman Bay, and two years ago Maryland biologists found it widespread in the state's coastal bays.

The organism seems to thrive in salty, shallow bays like those along Maryland's Atlantic shore. and as the bays receive more sewage and other pollutants from shoreline development, DNR scientists worry that these waters provide close to ideal conditions for the brown tide blooms.

in late may, for the second straight year, dense brown tide blooms appeared in the Newport Bay south of Berlin and at the Public Landing east of Snow Hill. said David Goshorn, the DNR's harmful algae expert.

The blooms seemed to be fading in late June as water temperatures reached 80 degrees - the upper limit of what Aureococcus can tolerate - but there is a good chance they will reappear in the fall when the water cools, Goshorn said.

No one knows what triggers brown tides - at a recent conference the scientists proffered eight hypotheses - but nutrient pollution is believed to be a factor.

Farther north in Long Island Sound, brown tides have been linked to New York City sewage outfalls and have devastated a once-thriving scallop fishery. The organism may kill scallops by preventing them from feeding. and may also deter them from reproducing.

Brown tide algae slow the growth of all type of sea life, experts say. Worthless as fish food, the dense blooms crowd out other more nutritious algae. Brown tides also damage sea grass beds, which are essential shelter for marine creatures, by blocking the sunlight the grasses need for photosynthesis.

Chattonella Verruculosa

When dead fish turned up in Delaware's Indian River in August last year, that state's officials initially blamed it on natural causes: low oxygen levels in the water. But a surfer sent a sample of the yellow-tinged water from where the fish kill occurred to a North Carolina Laboratory, where the experts identified traces of Chattonella verruculosa, algae responsible for red tides and fish kills in Japan and Norway.

Delaware officials were unable to tie it to their fish kill, but soon afterwards Maryland's DNR noticed that the algae in three tributaries feeding into the state's coastal bays. The organism hasn't shown signs of being toxic in state waters though scientists say they have much to learn.

"We're really new to this organism," said the DNR's Robert Magnien. "The discovery in Maryland and Delaware is the first it has been documented in this area."

In Europe and Japan, a form of Chattonella has swept through the stocks of caged fish on farms. killing virtually all of them. In the United States, Chattonella is elusive and poorly understood, according to Joanne Burkholder, a harmful algae expert at North Carolina state University. Though call golden brown algae, it's actually green, and it changes shape frequently, making it hard to identify.

The organism lives in brackish or salty water and seems to thrive in water temperature between 70 and 80 degrees, Burkholder said.

Chattonella has been found in Florida North Carolina waters, and several strains have been found in Maryland and Delaware, Burkholder said.

In its toxic stage, it produces three compounds similar to the ones found in the red tides. The toxins an kill fish and afflict people with watery eyes, runny noses, wheezing and skin rashes. people eating shellfish tainted with these toxins could suffer neurological problems, Burkholder said.

On Delmarva, "It's a question mark.", she said. "It hasn't really been verified to be toxic, but it's worth watching."

Blue-Green Algae

At least one dangerous strain of algae is less common than it used to be in parts of the Chesapeake Bay.

Blue-green algae blooms in the Potomac River have declined greatly since the 1960's and 1970's, when the river was so polluted by sewage that the thick algae mats regularly coated its surface.

The blooms which tend to peak in late summer, often look as if someone poured green paint on the water. Sometimes sparkling flecks are visible near the surface.

"It's best not to swim in those waters.' said Robert Magnien of the Department of Natural Resources. The freshwater algae can be toxic, he said.

Every summer there are reports from polluted urban lakes in the United States and Europe of dogs getting in the water during a bloom, licking the algae off their fur and getting sick or dying.

The cyanobacteria that cause the bloom, called Microcystis aeruginosa, can trigger skin irritation and gastrointestinal problems in people. Its toxin can also damage the liver, said Joanne Burkholder of North Carolina State University.

In mid-June, biologists found low to moderate levels of the algae on the lower Potomac near Indian Head and on the Sassafras River near Georgetown, Del.

Like other species, dense blooms of the blue-green algae can damage underwater grasses by blocking sunlight, and can cause fish kills by consuming all the oxygen in the water.

The algae bloom to some of the bay's freshwater tributaries most years. Last year, blooms reached the open bay, covering about half of the area Susquehanna flats to the Bay Bridge. DNR biologist blamed late-summer rains that kept the bay waters fresh and washed nutrients into the bay to fuel algae growth.

As summer progresses, biologists expect to see Microcystis blooms on the Sassafras and Bohemia, where they occurred frequently since the 1980s. Blooms seldom reach the bay, but the rainy late summer could make that happen again this year, Magnien said.


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