Monitoring rivers for clues

Pfiesteria: Although no major outbreak of the deadly microorganism has occurred since 1997, scientists are studying what triggers its toxic state.


There's an algal bloom just downstream from Shelltown on the Pocomoke River. And there are plenty of menhaden, the fish Pfiesteria feast on. State biologists even found the deadly microorganism, albeit in a benign state, in water taken from the river late last month.

These conditions resemble the summer of 1997, the year an outbreak of Pfiesteria piscicida killed fish and sickened people along three rivers on Maryland's lower Eastern Shore. But that doesn't necessarily mean Shore waters are in for another outbreak of lesioned fish circling crazily near the surface before they expire or of people suffering memory loss and disorientation.

Scientists don't know enough about Pfiesteria to make that prediction, says Dave Goshorn, a biologist for Maryland's Department of Natural Resources: "One of our great frustrations is we'd like to be able to say there's `X' percent chance of a Pfiesteria outbreak, but we can't."

Scientists know that Pfiesteria is a dinoflagellate, a one-celled organism that has many stages in its life, most of them nontoxic, and that it can exist in bottom mud as well as in the water.

They also know that Pfiesteria eat algae -- and that when an algal bloom appears in shallow, slow-moving water, there's a good chance Pfiesteria is there also, says Rob Magnien, head of DNR's Pfiesteria programs. They even can tell you that Atlantic menhaden emit something that attracts Pfiesteria, Magnien says.

But what that is, and what triggers the toxic state, is under study.

No major outbreak of toxic Pfiesteria has occurred since 1997, but scientists on the Delmarva Peninsula have been taking water samples and monitoring fish from April to October for the past two years. They are looking for clues that will help them understand why Pfiesteria turns toxic and predict when it might happen again.

"We're developing a baseline so that if we have an outbreak we can look at what we have and see what the differences are, what the changes have been," said John Surrick, DNR spokesman.

DNR biologists have drawn samples from the rivers affected in 1997 -- the Pocomoke, the Chicamacomico and Kings Creek in the Manokin River system -- and five others, the Nanticoke, Wicomico and Big Annemessex, which flow into Chesapeake Bay, and Trappe Creek and the St. Martin River in the Coastal Bays. They also are examining fish in those waters.

Surrick says the five streams were chosen because they are similar to the rivers affected in 1997 and might be susceptible to Pfiesteria outbreaks.

DNR biologists Tim Herb and John Christmas make their rounds every two weeks in a blue van with a make-shift laboratory in the back, drawing buckets of water from spots such as New Bridge on the Chicamacomico in Dorchester County.

They pour some of the water into a device that gives them readings on temperature, salinity, oxygen and acidity. More water goes through filter pads to test for nitrogen, algae and chlorophyll. "You can have a little chlorophyll, but a lot of chlorophyll kills the underwater grasses, and the fish won't have anything to eat," Herb says.

The water and the filter pads are put in carefully marked color coded tubes and envelopes and sent to University of Maryland laboratories at Solomons Island and Horn Point for more tests. One sample goes to the virology lab at the UM School of Medicine in Baltimore, where Dr. David Oldach has developed a quick, relatively inexpensive test to determine whether Pfiesteria is present.

Scientists have learned enough about Pfiesteria to be able to "clone the genes" of the organism and compare them with the samples to determine whether Pfiesteria is present, Oldach says.

It was Oldach who found Pfiesteria in a sample taken from the Pocomoke June 24.

"We've been sending him 50 samples a month, and we hadn't found anything until the sample on the Pocomoke," Goshorn says.

Neither Goshorn, Oldach or others involved in Pfiesteria research were surprised.

"We've found it there before," Goshorn said. "And from what we know about the organism, it spends most of its life in its nontoxic stage."

While there are no tests to determine whether Pfiesteria is in its toxic state, officials assume the Pfiesteria that Oldach found was benign because they also have been monitoring fish and haven't seen any with the characteristic lesions.

"We've looked at tens of thousands of fish and not seen anything of any major significance," Surrick said.

Biologists found sores or other kinds of anomalies on fewer than 1 percent of the 50,000 fish they examined between June 19 and July 2, according to a DNR report issued this week.

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