Coastal Heritage Magazine
Pfiesteria Hysteria: Just When You Thought It Was Safe
Over the past two decades, scientists have discovered dozens of new species of nuisance algae that raise havoc around the world, killing huge numbers of fish and causing human illnesses. The most famous new species is Pfiesteria piscicida, found in estuaries from Delaware to Florida. Although Pfiesteria is often described as a bizarre, freakish phenomenon, it is just one small part of an international problem.
A Closer Look. David Strickland, technician with the S.C. Department of Natural Resources, examines a menhaden with a lesion. Photo by Wade Spees.
Coastal Heritage Magazine
Volume 13 – Number 2
Pfiesteria Hysteria: Just When You Thought it Was Safe
Last year, public fascination with Pfiesteria piscicida—a toxic organism nicknamed the “cell from hell”—reached dizzying new heights. Previous Pfiesteria outbreaks in North Carolina had received widespread news coverage. But when fish kills were linked to Pfiesteria in Maryland in 1997, and the state closed portions of three rivers that flow into the Chesapeake Bay, the national press swarmed in a frenzy.
Suddenly, a toxic dinoflagellate was a major news event in the nation’s capital. For months, headlines blared about the eerie, microscopic creature that lurked in calm, shallow bays, attacking and killing massive numbers of fish. Congressional committees demanded to know why these outbreaks occurred. The Maryland seafood industry lost an estimated $45 million due to negative publicity, although Pfiesteria has never been linked to food poisonings.
Why did Pfiesteria get so much ink? Pfiesteria piscicida is just one of many species of harmful algae, though it gets nearly all the media’s attention. News organizations have never focused on other nuisance algae to this extent. In fact, harmful algae affect nearly all U.S. coastal waters.
Harmful algae have caused about $40 million annually in damages to U.S. fisheries, public health, and tourism since 1991, says Donald Anderson, Woods Hole Oceanographic Institution marine scientist. Along the West Coast and in Alaska, state officials have closed hundreds of miles of coastline to shellfish harvesting due to toxic algae. In New England, nuisance blooms over the past two decades have killed shellfish, lobsters, fish, and marine mammals. In 1988 alone, blooms killed vast numbers of scallops in New York waters, causing a $2 million loss to that state’s shellfishing industry.
On the Cover. An unusual toxic algal species, Pfiesteria piscicida, has touched our fears of going into the water. Photo by Wade Spees.
Toxic algae can be dangerous to human health as well. Around the world, thousands of people are poisoned annually by eating shellfish or tropical fish contaminated by algal toxins, experts say.
The number of harmful algae seems to be growing internationally, too. A decade ago only about 25 toxic species had been identified, but now scientists believe that about 60 to 80 are toxic, according to Sea Grant researcher Theodore Smayda, oceanographer at the University of Rhode Island. The geographic distribution of harmful algae is spreading as well. “Toxic blooms are occurring in places where they haven’t been seen before,” says Patricia Tester of the National Oceanic and Atmospheric Administration’s (NOAA) National Marine Fisheries Service. And several new algal poisons have been discovered. “We’ve found new toxins that we didn’t know existed,” says Anderson.
To Catch a Thief. With a special microscope, research technician Bonnie Willis is helping scientists learn to what degree Pfiesteria piscicida steals the chloroplast from nontoxic algae. With stolen chloroplast, Pfiesteria can use photosynthetic energy to survive longer in estuaries. Photo by Wade Spees.
About two-thirds of toxic species, including Pfiesteria, are dinoflagellates—microscopic, single-celled organisms with tails or flagella that enable them to travel by spinning through the water.
While the overwhelming majority of dinoflagellate species are not harmful, some can accumulate near the sea surface and discolor the water. These are called “red tides,” which usually have benign effects, though some species both redden the water and produce toxins. Other dinoflagellate species, like Pfiesteria, produce toxins without coloring the water.
So Pfiesteria is not so unusual in some respects. Yet by following press reports, you could think that Pfiesteria is the only toxic algal species on earth, even when some of its environmental impacts have been relatively minor. While Pfiesteria has killed many millions of fish in North Carolina, the total number of Chesapeake Bay fish deaths blamed on the organism in August and September 1997 was only about 50,000. By contrast, a toxic bloom of another dinoflagellate, Gymnodinium breve, killed about 14 million fish off the coast of Texas in September and October of 1997—and the national press mostly ignored it.
Plumbing Pfiesteria’s Mysteries
Pfiesteria is frightening partly because scientists have been stumped by many of its mysteries. “We don’t know enough about the organism,” says Alan Lewitus, marine scientist at the University of South Carolina’s Belle W. Baruch Marine Laboratory. “It is new and unusual, more elusive and adaptable than other toxic species,” and therefore harder to study and understand.
Perhaps Pfiesteria strikes at a vulnerable spot in our psyche—the fear of a horrible creature lurking below the surface of our favorite swimming hole. Jaws and other bone-chilling movies have played on these elemental fears. The emergence of Pfiesteria could touch our “insecurity about going into the water,” says Lewitus.
Casting for Research. With Matt Schwartz at the wheel, S.C. Department of Natural Resources technician David Strickland casts for menhaden to monitor the fish for lesions. In about 3,000 menhaden sampled in South Carolina waters, researchers have found lesions in 15 fish. These fish sores are consistent with the effects of toxic Pfiesteria, but also with the effects of viruses and bacteria. Photo by Wade Spees.
Most of the time, though, Pfiesteria is a nontoxic organism that lives on the estuary bottom, consuming bacteria, algae, and other tiny creatures. But when it detects big schools of fish—by sensing their excrement or secretions—the dinoflagellate swims up and releases a paralyzing poison. This toxin strips skin from fish and causes bleeding sores.
While fish are dying, the organism consumes their blood and skin. Then great numbers of the toxic dinoflagellates are attracted to the kill, and in the feeding frenzy they rapidly reproduce, says JoAnn Burkholder, a North Carolina State University botanist.
Once the feeding is complete, Pfiesteria will drop back to the bottom, changing shape and turning into a nontoxic cyst, one of its 24 life stages.
Researchers have been frustrated by the organism’s ability to disappear from their detection, leaving only fish carcasses behind. “Its behavior—attack and retreat—makes the organism difficult to sample,” says Lewitus. “Pfiesteria’s toxic stages are ephemeral, and we can’t detect them yet. With other algae, we can sample the water and find the toxic species.”
Blooming Pfiesteria. Alan Lewitus, marine scientist with the Belle Baruch Marine Laboratory, is studying the causes of Pfiesteria blooms. Photo by Wade Spees.
To complicate matters, Pfiesteria piscicida is not alone out there. Several small dinoflagellates resemble it in general appearance. Some of these 6 to 8 so-called “Pfiesteria look-alikes” are also toxic, but otherwise have different behavior patterns and life cycles than Pfiesteria piscicida.
Most toxic algae harm people through a single pathway: contaminated seafood. Pfiesteria, on the other hand, seems to affect people only when its toxins are inhaled or absorbed through the skin.
“This is a potentially new route of exposure to an algal toxin,” says Adam Karpati, medical epidemiologist at the Centers for Disease Control and Prevention (CDC), based in Atlanta.
When airborne, some red tide toxins have direct effects on human lungs, causing asthma. But Pfiesteria is the only known algal toxin that apparently is absorbed through skin or lungs, causing systemic effects on human health, including memory loss and other neurological symptoms.
Even so, “the evidence of its human health effects is scanty,” notes a CDC report, perhaps due a lack of clinical studies. In the only such study to date, a team of medical specialists from Johns Hopkins University and the University of Maryland examined a small group of people who swam or worked in Maryland’s Pfiesteria-infested waters, diagnosing them with a condition called Estuary Associated Syndrome, with symptoms of confusion, disorientation, skin rashes, and headaches. All subjects recovered.
But if people avoid fish kills, they are probably safe in the water, some researchers say. A North Carolina Sea Grant research team interviewed by telephone 253 crabbers who worked in estuaries with a history of Pfiesteria-related fish kills, 115 crabbers who worked in unaffected estuaries, and 125 nonfishing residents of communities where crabbers lived. People were asked about illnesses and injuries that could be associated with algal toxins. All subjects had avoided fish kills and other signals of pollution.
“We thought we were going to find many cases of Pfiesteria-related illnesses,” says David Griffith, East Carolina University anthropologist who has studied fishing communities and labor issues in the seafood industry. Crabbers, compared to nonfishermen, suffer a high rate of skin problems—including skin cancers probably associated with their line of work. But crabbers working in waters with a history of Pfiesteria outbreaks did not have a statistically significantly higher incidence of illness than those working in unaffected areas.
The peer-reviewed study suggests that casual contact with North Carolina waters poses little or no health risks, as long as people stay away from fish kills. “If you consider how many people work and recreate on the water, it’s striking how few reports of human illness we have,” says Griffith. Karpati notes that this retrospective study is “reassuring, but it doesn’t rule out the existence of Pfiesteria-related illness. Pfiesteria could cause quite subtle symptoms that people may not report or remember or associate with polluted water.” Some Mid-Atlantic states are establishing their own studies of Pfiesteria effects, coordinated by the CDC.
In any case, Pfiesteria toxins are dangerous in inadequately ventilated areas. Burkholder and her assistant suffered memory loss and other health problems after working with the organism in a laboratory. So now the toxic algae must be grown only under strict biohazard conditions, and a facility has been built at North Carolina State University for this purpose. But these safety guidelines limit the amount of algae that can be grown in a laboratory, thus restricting research on the poison.
There is not sufficient algal material, so researchers have had difficulty studying the toxin, notes John Ramsdell, division chief of the NOAA National Ocean Service’s Charleston Laboratory marine biotoxin program. Scientists can’t determine how people are being affected by the organism until they know how to detect the poison’s presence.
Nevertheless, scientists at the NOAA Charleston Laboratory and other institutions have made progress in isolating the Pfiesteria water-soluble and lipid-soluble toxins. Molecular probes to detect the presence of Pfiesteria and its toxins in the field are being developed by Ramsdell and Parke Rublee of the University of North Carolina at Greensboro. Such probes are biochemical tools that can identify the presence of molecular traits of specific organisms.
The probes could help researchers determine whether fish kills are actually caused by the organism. “During fish kills, we could use the probes to identify Pfiesteria if it’s the cause,” says Lewitus.
Excess nutrients have contributed to an overgrowth of nontoxic algal blooms worldwide. Satellite images have confirmed increases in the size and scope of algal growth during the 1980s and early 1990s.
But in many cases, scientists cannot find a cause-and-effect relationship between excess nutrients and toxic algal blooms. This is true of Pfiesteria as well.
Nevertheless, there is an indirect link between nutrients and Pfiesteria blooms. Take the example of North Carolina’s Neuse River, which was closed in 1995 after fish kills were linked to toxic algae. The river begins in the Piedmont, home to the state’s largest cities and many farms and forestry operations. Nutrient levels in the Neuse have tripled over the past 100 years, experts say.
Excess nutrients in the Neuse come from synthetic nitrogen fertilizers used in agriculture, nitrogen oxides discharged by cars and factories, urban runoff, and sewage-treatment plants. A portion of these nutrients flows from hog farms; the hog population doubled in the Neuse watershed from 1990 to 1995. Millions of gallons of manure, rich in nutrients, have spilled from farm ponds and run off fields into waterways during heavy rains. Farmers routinely spray livestock waste on fields, and heavy rains wash it into rivers.
Plankton feed on these nutrients, and in turn, Pfiesteria piscicida eats the growing populations of plankton, according to a recent study by Sea Grant researchers Hans Paerl and James Pinckney of the University of North Carolina.
But for outbreaks to occur, other environmental factors must also come into play: slack or poorly circulating brackish water, warm temperatures, and large schools of fish.
Pfiesteria should be grown only under strict biohazard conditions. A facility has been built for this purpose at North Carolina State University, as shown here. The safety guidelines have restricted the amount of Pfiesteria that can be grown in a laboratory, limiting research on its toxins. Photo courtesy Burkholder Laboratory.
Task Force Takes Action
Recent Pfiesteria blooms and fish kills have received massive publicity partly because they’ve been found in economically valuable ecosystems. Fishing and tourism industries in Maryland and North Carolina depend on the Chesapeake Bay and the sounds of North Carolina, and these industries have been harmed by public panic over Pfiesteria. The timing of the outbreaks has been important, occurring during warm-weather months when people are fishing, swimming, and boating in waterways.
When coastal residents read about toxic organisms in local estuaries, some believe their prized ecosystems are degraded and unsafe, a sign of a broader environmental crisis, researchers say.
Now officials must respond aggressively to public concerns, even if the threat to human health is probably minor. Over the past year, for example, South Carolina scientists, physicians, and resource managers have established a task force to study the toxic organism, monitor water conditions, set up health-care networks, and establish public-information campaigns.
State officials are investigating all reports of fish kills, which are thoroughly sampled to determine whether Pfiesteria is present, says Butch Younginer of the S.C. Department of Health and Environmental Control (DHEC).
Educational programs are being designed for physicians to aid accurate diagnosis of Estuary Associated Syndrome, says Robert Ball, epidemiologist at the S.C. Department of Environmental Control (DHEC). Public-education programs will describe common-sense measures for the public to follow. “If you see a fish kill, don’t go (near it) in the water,” said DHEC epidemiologist Jerry Gibson.
If outbreaks do occur in South Carolina, they will likely be found in poorly circulating waterways such as the Sampit River, says Fred Holland of the S.C. Department of Natural Resources. It’s possible that major Pfiesteria outbreaks would not occur in South Carolina, perhaps because the state’s estuaries “are generally well-flushed and relatively unaffected by nutrients,” Lewitus says.
Now the task group is seeking to reassure the public. “Our waters are safe to swim in, our seafood is safe to eat, and we, working together, want to keep them that way,” says Rick DeVoe, executive director of the S.C. Sea Grant Consortium.
Danger Zones: Mapping Growth of Toxic Algae
Although toxic algae have spread geographically in recent years, seafood in the United States is still safe to eat due to rigorous monitoring efforts.
In April 1992, a fishing party of seven was camped along the coast of British Columbia when two of the men cooked and ate butter clams and cockle clams harvested from Moore Bay. After complaining of numbness around their mouths and lips, the men collapsed, becoming paralyzed and unable to breathe, their bodies turning blue. Their companions performed artificial respiration and radioed the Coast Guard. Helicopters arrived 45 minutes later, and after treatment in a nearby town the victims were flown to a Vancouver hospital, where they were put on ventilators. Both men, fortunately, survived.
The fishermen had eaten shellfish contaminated with the toxic alga Alexandrium. They suffered a condition in which the nerve impulses do not get to diaphragm muscles, so the lungs fail.
Alexandrium is among dozens of species of toxic algae that cause seafood poisoning. Clams, mussels, scallops, oysters, and other shellfish filter plankton, including toxic algae, from the water, and the toxins accumulate in their tissues, frequently without great effect to shellfish health.
But after eating the seafood, people can suffer gastrointestinal disorders, respiratory problems, confusion, memory loss, and, in rare cases, death. One clam or mussel can hold enough poison to kill a human being. What makes such toxins especially dangerous is that they are tasteless and colorless, and cooking shellfish often won’t destroy them. In one instance, there is an algal toxin that can be aerosolized by surf, carried by breezes inland, and cause respiratory problems.
Source: National Office for Marine Biotoxins and Harmful Algal Blooms, MS #32, Woods Hole Oceanographic Institution, Woods Hole, MA.
The first recorded fatal cases of shellfish poisoning occurred in 1793 after Captain George Vancouver and his crew landed along the northwestern coast of North America. Some of Vancouver’s sailors ate shellfish from an area known today in British Columbia as Poison Cove. Later, Vancouver learned that local Indians would not eat shellfish during dinoflagellate blooms, which reddened the waters.
Still, scant information exists about the prevalence of marine seafood poisonings. There are rough estimates of perhaps 60,000 toxic seafood poisonings worldwide each year. But the great majority of cases are not reported or are misdiagnosed, which is typical for all kinds of food poisonings. For example, fewer than 0.3 percent of disease outbreaks from all contaminated foods are reported to the federal Centers for Disease Control and Prevention (CDC).
The CDC lacks a surveillance system for keeping track of seafood poisonings from algal toxins. Some states require that physicians report cases of specific marine seafood poisonings to the state health departments, however, and these numbers are sent to the CDC.
Although data are fragmentary, it appears that algal poisonings are increasing along with interstate and international shipping of seafood. International travel has exploded as well, with greater numbers of people eating seafood in exotic places. But in the United States, illnesses due to toxic algae are rare, largely due to careful monitoring of shellfish beds by coastal states. “States have sophisticated, rigorous shellfish monitoring programs,” significantly reducing risks of consuming tainted food, says Adam Karpati, CDC medical epidemiologist.
Types of Toxic Algal Blooms
The oldest known toxic algal species in North America is a dinoflagellate that causes neurotoxic shellfish poisoning (NSP). After people eat contaminated shellfish, they can suffer numbness and tingling, cramps, nausea, vomiting, diarrhea, chills and sweats. During blooms, this dinoflagellate’s toxins also kill fish, invertebrates, birds, and marine mammals. When NSP blooms are aerosolized in surf, the toxin becomes airborne and can cause respiratory problems in people.
NSP is the best documented illness caused by a harmful algal species. Centuries ago, Tampa Bay Indians and Spanish explorers noticed fish kills in certain seasons when coastal waters turned red. In 1880, shellfish poisonings were reported along the west coast of Florida, and in 1916 the first complaints about respiratory problems were recorded. In 1946, the dinoflagellate Gymnodinium breve was discovered as the culprit of NSP.
G. breve grows naturally offshore, on the continental shelf, using low levels of nutrients. But G. breve blooms are also transported inshore by currents. In coastal bays and canals, the blooms apparently last longer when stimulated by nutrients.
Researchers once believed that G. breve exclusively inhabited the Gulf of Mexico. But in 1987–88, the Gulf Stream carried G. breve to the east coast of Florida and pushed it farther north. Eventually, toxic blooms were pushed into North Carolina for the first time, and shellfish beds were subsequently closed for months, with 48 documented cases of human illness from shellfish poisoning. The regional economic impact of the shellfish-bed closing was estimated at $25 million.
A second category of harmful algal blooms occurs when one of several related species of dinoflagellate in the genus Alexandrium contaminates shellfish, causing paralytic shellfish poisoning (PSP), which can be life-threatening to humans.
Symptoms include tingling, numbness, drowsiness, fever, and in the most severe cases, respiratory arrest within 24 hours after the victim has eaten contaminated shellfish. Alexandrium species can also kill fish, birds, and marine mammals.
PSP affects more coastline in the United States than any other harmful algal illness. On the East Coast, PSP occurs frequently from Maine to Massachusetts, and occasionally farther south to New Jersey. From 1991 to 1995, PSP occurred each year from northern California to Alaska. Since 1988, 51 cases of PSP have been reported by state health departments in Washington and Alaska.
Nutrients probably are not driving these blooms. Alexandrium can grow in “relatively pristine waters,” says a February 1997 NOAA report. The annual appearance of PSP since 1991 on the West Coast is probably due to improved detection methods and to communication among scientists, says Donald Anderson, Woods Hole Oceanographic Institution marine scientist.
A third class of harmful algae causes amnesic shellfish poisoning (ASP), which can also be life-threatening. Diatoms in the genus Pseudo-nitzschia produce domoic acid, a neurotoxin that can cause nausea, vomiting, cramps, and diarrhea. In severe cases, neurological symptoms occur within 48 hours of consumption of toxic shellfish.
Victims can suffer dizziness, seizures, disorientation, short-term memory loss, respiratory difficulty, and coma. In 1987, four Canadians died and 105 more suffered permanent short-term memory loss after eating mussels contaminated with toxic diatoms harvested off the coast of Prince Edward Island.
Toxic Pseudo-nitzschia species also bloom in the Gulf of Mexico and along the West Coast. In May 1998, domoic acid in harmful algal blooms killed nearly 80 juvenile and adult sea lions off the California coast.
Few Worries. Seafood poisonings are rare in the United States due to rigorous shellfish monitoring programs. Photo by Wade Spees.
In 1991, a few people became ill in Washington state after consuming razor clams contaminated by toxic algae. The victims suffered mild, short-lived symptoms, including gastrointestinal disorders and memory loss.
Most Pseudo-nitzschia blooms have not been linked to nutrient enrichment but instead to natural events, including spring and summer changes in currents, temperature, and salinity.
In the tropics and subtropics, toxic dinoflagellates living on coral reefs are eaten by herbivorous fish, which in turn are eaten by larger carnivores. The poisons moving up the food chain cause ciguatera fish poisoning (CFP), a fourth category of algal toxicity. Symptoms include numbness and tingling, cramps, nausea, vomiting, diarrhea, chills, and sweats.
More than 400 different fish species can be associated with ciguatera poisoning, including groupers, barracudas, snappers, jacks, mackerel, and trigger fish, according to a 1996 report by the Intergovernmental Oceanographic Commission.
This form of seafood poisoning is one of the most serious public health threats from harmful algae in the United States and its territories, says Anderson. Between 1988 and 1992, 165 cases of ciguatera poisoning were reported to the CDC. Isolated poisonings occur from south Florida to Vermont, with more regular ones in Hawaii, the U.S. Virgin Islands, and Puerto Rico.
But the great majority of ciguatera poisonings are unreported, says Anderson. An estimated 100 cases of poisonings are unreported for every reported case in Puerto Rico and the Virgin Islands, where many people are “so poor they don’t go to the hospital,” Anderson says, and three of every four cases are unreported in Florida.
Scientists Search for Explanations
To explain increasing appearances of harmful algae worldwide, some researchers point to nutrient over-enrichment, but others point to greater monitoring of cultured seafood and coastal waters, which has revealed toxic algae that probably always existed.
Another explanation is that harmful algae are being transported from estuary to estuary by ship ballast water. Merchant ships routinely draw ballast water into their holds to provide additional weight, making them ride lower and offering greater stability in the open ocean. This ballast water is often rich with aquatic creatures, including some toxic algae, which are released into new environments.
El Nino, which brings heavier rainfall and warming to some regions, also has aided the emergence or resurgence of harmful blooms, says Paul Epstein, associate director of Harvard University Medical School’s Center for Health and the Global Environment. Other “environmental stresses” that encourage blooms include overharvesting of fisheries that feed on plankton and destruction of wetlands that filter nitrogen and phosphorus, Epstein notes.
Cutting Nutrients Improve Water Quality
Excess nutrients in coastal waters is a major dilemma worldwide. In 1997, the Ecological Society of America and the international Scientific Committee on Problems of the Environment (SCOPE) called nitrogen pollution a “preeminent problem.”
Globally, people add between 7 million and 35 million metric tons of nitrogen and between 1 million and 4 million metric tons of phosphorus to the environment each year, says Walter V. Reid, vice president for programs at the World Resources Institute, a nonpartisan research organization in Washington, D.C. “Humans now have a huge impact on chemical cycles,” he says.
In the coastal ocean off the northeast United States, nutrient loads are 5 to 10 times higher than they were a century ago, and in the Gulf of Mexico they are 3 times higher, says Robert Howarth, Cornell University biogeochemist and co-chair of SCOPE.
But Donald Anderson, Woods Hole Oceanographic Institution marine scientist, disputes the idea that nutrient levels from human sources have boomed recently in U.S. waters. “During the past 20 years, there have been slightly elevated levels of nutrient pollution,” he says. “But overall, our coastal waters are in pretty good shape” largely due to sewage-treatment improvements under the federal Clean Water Act.
Some harmful algae kill farmed and wild fish but do not directly affect human health.
In recent years, for example, New York and Texas coastlines have been under siege by brown tides, which shade plant life in shallow bays.
In 1985, the first known brown tide appeared off Long Island and ruined the local bay scallop industry. In 1989, a brown tide bloomed off the Texas coast and remained there for eight years.
Researchers hypothesize that a “brown tide toxin influences nerve transmission in shellfish,” says Sea Grant researcher Darcy J. Lonsdale, marine scientist at State University of New York at Stony Brook. The brown tide algae could have evolved their toxins to ward off shellfish, one of their main predators.
The toxin prevents shellfish gills from functioning, so the shellfish can’t feed and thus will starve. Brown tide species could be stimulated, at least in part, by excess nutrients from human sources, some scientists say.
Harmful Algal Blooms in Coastal Waters: Options for Prevention, Control and Mitigation. A National Oceanic and Atmospheric Administration report. Edgewater, Md.: Chesapeake Research Consortium, 1997.
Design and Implementation of Some Harmful Algal Monitoring Systems. Paris, France: Intergovernmental Oceanographic Commission. 1996.
Research on Toxic Algae: Pfiesteria-Like Organisms. Final Research Report. Raleigh: North Carolina Sea Grant College Program, 1998.