Algae may be responsible for Chesapeake fish kills N.C. researchers find toxic species

December 03, 1991|By Liz Bowie

Sneaky little algae that pop up from the mud of a bay, attack fish with a deadly toxin, then quickly retreat may explain some mysterious fish kills in the Chesapeake and other East Coast waters.

North Carolina researchers recently discovered the new species -- nearly by mistake -- then found it at the scene of a crime: a major fish kill in May in Pamlico Sound along the coast of North Carolina. While scientists have not yet looked for the algae species in Chesapeake Bay waters, it has sparked their curiosity because it could explain numerous fish kills, particularly of menhaden, in the Chesapeake and tidal portions of its tributaries.

"Fish diseases and unexplained fish kills have been dramatically increasing in our estuaries. And around the world there is a lot of evidence beginning to accumulate that there are increasing numbers of toxic algaes," said JoAnn M. Burkholder, who discovered the algae.

Some scientists have speculated that the increase in these algae is a result of pollution, in particular phosphorus and nitrogen, both common in the Chesapeake. "I think the algae have always existed, but we are creating a more hospitable environment for their growth," said Dr. Burkholder, assistant professor of aquatic botany at North Carolina State University in Raleigh.

Maryland Department of Natural Resource fisheries scientists will begin looking for the algae this spring and summer, said Eric May, coordinator of the fish disease program at the DNR. But he cautioned there is only circumstantial evidence of the algae and some laboratory findings.

However, he said, the algae would explain some thousands of deaths of menhaden, an important species of fish harvested for use as bait in crab pots and for its oil. In those cases the fish died after they were seen spinning around disoriented.

The algae might also be linked to other fish kills in Maryland, which average about 22 a year and involve about 50 to 100 fish each time.

A search for the algae began when Dr. Edward J. Noga, an associate professor at the North Carolina School of Veterinary Medicine, brought some water back from the Pamlico Sound to grow fish in. Everything died.

He checked the water sample for heavy metals and pesticides and other likely suspects but couldn't find a culprit, until he found a microscopic plant.

Later tests showed that the algae killed everything from guppies to goldfish to flounder, menhaden, croaker and spot in the laboratory.

The next step was to find it in nature. In May, North Carolina biologists sampled water while fish were dying in the Pamlico Sound and found the new species. Since then, it has been found during several other fish kills, and 1988 records implicate it in 25 percent of the kills that year in North Carolina.

One of the reasons the toxic algae went undetected is that they are so sneaky. During most of its life, the alga wraps itself in V VTC hard shell and sits like a blob on the bottom of a river or bay. When it picks up the scent of fish above -- probably the excretion of an amino acid in fish -- it emerges and hands out a toxin so potent it kills fish in minutes. "As soon as the fish are dead, it loses interest and goes back down," she said.

So unless researchers sampled the water during the time of the kill, they could not find the algae, which is currently unnamed.

"We did have frequent sightings of spinning menhaden, but we could never get our collective acts together so that we could be on top of the menhaden while they were dying," Dr. May said. Because the fish die so quickly from the toxin, there is little likelihood that either humans or other fish would consume a stricken fish.

However, Ms. Burkholder said, in the laboratory, the toxin may accumulate more slowly in shellfish and could present a risk to humans.

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