The Feeding Frenzy of a Morphing `Cell From Hell'

RALEIGH, N.C. -- Each day, a fresh batch of 70 fish are prepared for sacrifice to the strange beast in JoAnn Burkholder's lab. The fish are placed alive in what appear to be empty aquariums, but in as little as 10 minutes they're dead. Some are covered with hideous sores, the trademark of the creature Burkholder calls "the cell from hell."

 "We put live fish in and we take dead ones out," observes Burkholder, an aquatic botanist with North Carolina State University. She watches the spectacle from behind a mask and a protective suit, knowing too well that the beast's venomous "bite" can harm people, too.

 Invisible to both scientist and fish is the creature itself, a bizarre one-celled predator that can appear to transform itself from animal to plant and back again. Called Pfiesteria piscicida, this killer dinoflagellate captured the attention of scientists worldwide when it emerged six years ago from the murk of North Carolina's coastal estuaries, the phantom suspect in a string of mass killings that destroyed more than a billion fish.

 Back then, it seemed weird and exotic. But after years of study -- and after new findings that confirm Pfiesteria's presence in the Chesapeake Bay and other coastal waters -- Burkholder and other scientists are convinced that the creature is not a curiousity, but a warning.

 The new view places Pfiesteria among the ranks of other harmful microorganisms, including the ones causing the toxic "brown tides" that are battering fisheries in New England and Texas. For millennia, these creatures marked time in the outer fringes of coastal ecosystems. But in recent years, pollution has shifted the natural balance and created an opening for opportunists that thrive in waters rich in sewage, animal waste and fertilizers from burgeoning coastal settlements.

 Like the algae blooms that plague European seaports and the "red tides" that kill Florida manatees, Pfiesteria may be yet another sign that humans are changing coastal environments in ways that could have serious consequences for wildlife and people, scientists say.

 "We are getting to the point where we are creating new kinds of ecosystems -- ones that function in a completely different way," says B.J. Copeland, a marine ecologist and former head of the N.C. Sea Grant program. "And this is not the end. We're going to see other kinds of strange things."

 For the moment, though, it's hard to imagine a creature as strange as Pfiesteria. In the universe of unicellular animals, it is something of a quick-change artist, slipping through at least 24 different guises at various points in its life cycle.

 Its ability to morph into wildly different forms makes it difficult to detect. When no prey is present, the creature can encase itself in a pod, or "cyst," and lie dormant in river sediment. It also can become a blob-like amoeba that feeds on microscopic algae. Sometimes it can even appear to become an alga, thanks to its ability to "steal" the chlorophyl-producing chloroplasts from its algae prey and use photosynthesis to supplement its nutrient supply.

 But in the presence of certain kinds of fish, Pfiesteria drops its pseudo-plant routine and turns into the microscopic sea monster that has inspired headlines around the world. As a dinoflagellate, it sprouts a whip-like tail, races to its prey and spews "multiple toxins," says Burkholder, who was the first to identify and name the creature.

 "One toxin strips the skin off the fish," Burkholder says. "Another affects the immune system, depressing the white blood cell count by 20 percent. Others affect the liver, kidneys, nervous system."

 No one knows exactly what triggers the kinds of Pfiesteria feeding frenzies that have plagued North Carolina's Pamlico and Neuse river estuaries in recent years. Tests in Burkholder's lab suggest the animal prefers dirty, nutrient-rich water, such as found near some municipal sewage outflow pipes. For those who have witnessed an attack, it is an experience not easily forgotten.

 The first sign is a "fish walk," the death struggle of thousands of fish flopping and thrashing on the water's surface. Some fish actually beach themselves, fleeing the water as though it were on fire.

 Within hours the river is clotted with mats of dead, sore-pocked fish that eventually will wash up on expensive riverside lawns in big, smelly heaps. But by that time virtually all traces of the killer have vanished: The newly engorged Pfiesteria quickly transform themselves into cysts and sink back into the mud of the riverbed.

 Crabbers and divers who worked in Pfiesteria-infested waters have reported unusual sores, although a recent state health survey found no conclusive evidence of human health problems related to exposure to the organism or eating possibly tainted fish. Lab workers and rats exposed to high concentrations of Pfiesteria toxins have, however, developed a wide range of neurological symptoms, including confusion and short-term memory loss.

 Exactly how many North Carolina fish kills have been caused by Pfiesteria is in dispute. Some scientists suspect that the fish are dying for other reasons -- a lack of oxygen, mainly -- and that Pfiesteria are simply taking advantage of a free meal. Not so, says Burkholder, who is widely acknowledged as the leading authority on Pfiesteria, with 15 peer-reviewed studies to her credit.

 Ruling out fish kills where dissolved oxygen levels were low, Burkholder conservatively estimates that half of the dozens of fish kills she studied since 1991 were directly caused by Pfiesteria.

 So far, the most severe Pfiesteria attacks have been confined to North Carolina. But each year brings new discoveries of Pfiesteria, variations of which have been found as far north as Delaware's Indian River and as far south as Florida. Last month, Burkholder confirmed the presence of Pfiesteria in samples of water and fish taken from the Pocomoke River, which joins the Chesapeake Bay in southeastern Maryland. She now says Pfiesteria was "strongly implicated" in the recent Pocomoke River fish kill, though she was unable to determine whether the dinoflagellate alone had caused the fish to die.

 The discoveries of open, bleeding sores in fish from the Pocomoke and other Chesapeake tributaries have prompted concern among Maryland environmental officials, though there is no consensus about whether Pfiesteria might be responsible. U.S. Rep. Wayne T. Gilchrest (R-Md.) called a meeting of state and federal regulators this week to mull the latest evidence.

 Even a finding that Pfiesteria isn't the problem may not necessarily be good news. Gilchrest believes this year's cold, wet weather, combined with runoff from cities, farms and poultry operations, has created a nursery for a host of harmful organisms that could soon wreak havoc throughout the bay.

 "Catfish are dying in the Bohemia River. Rockfish are being found with open lesions bay-wide," he said. "We're seeing a phenomenon that our scientists have never seen before -- and didn't expect to see."

 Pfiesteria is a single-celled animal related to the toxic dinoflagellates that cause "red tides." It can assume as many as 24 different guises in its life cycle and can even masquerade as a plant. One of Pfiesteria's forms attacks, kills and eats fish.

 FISH EXCRETIONS in nutrient-rich waters trigger transformation of Pfiesteria cysts in the sediment and non-toxic zoospores.

 SWIMMING TOXIC ZOOSPORES attack fish, creating bloody sores, disorientation and death. The dinoflagellate feeds on damaged flesh. 

WITHIN HOURS of the fish kill, Pfiesteria drifts back to the sediment, where it exists as an amoeba or reverts into a cyst.