Fish diseases are rampant. From red tide to white plague,
from rapid-wasting disease to Pfiesteria hysteria,
the aliens are among us.
|Peter J.S. Franks
A spreading red tide, more than a mile off the coast of La Jolla, California, in April 1995.
In our twentieth-century fiction the alien invasion may come directly from outer space (War of the Worlds) or indirectly, from the scientific laboratory (The Andromeda Strain). But from the ballast water of ships? Or the shrimp farms of Ecuador? And while the shape-shifter may have been a character out of the Star Trek television series, the notion is not so out of this world. Such a creature already exists in our earthly realm in the form of a lethal microorganism that can assume at least two dozen different guises, known as Pfiesteria piscicida, “the phantom,” and the “cell from hell.”
In recent years, along the coastal and inland waterways of the United States and the world, these exotic arrivals have become frighteningly real. Plagues of often previously unknown microbes, viruses, parasites, and algal blooms are ravaging coral reefs, shellfish beds, rainbow trout, and even populations of marine mammals, including Florida’s endangered manatee. Some of the toxic predators are sickening humans as well. While the scientific community is divided about precisely what is causing many of the outbreaks, there is consensus that fish diseases are reaching epidemic proportions.
As Dr. George Woodwell, a prominent scientist with the Woods Hole (Massachusetts) Research Center and an NRDC trustee, describes the situation: “This is hardly unexpected. It’s all part of the general biotic impoverishment of coastal waters due to human-induced chemical, physical, and biological changes. This chronic disturbance leads to a simplification of basic structures. It favors small-bodied, rapidly producing organisms, from which come pests of all sorts, including those carrying disease.”
Let us begin by examining what experts call harmful algal blooms (HABs). An algal bloom occurs when algae – single-celled microscopic plants called phytoplankton that make up the base of the marine food chain – photosynthesize and multiply rapidly by converting dissolved nutrients and sunlight. Some algal blooms may prove lethal as the sudden abundance of algae depletes the oxygen that fish need to survive. Generally, however, most naturally occurring blooms are vital and beneficial to the marine food chain. Yet among the thousands of algal species a few dozen exist that are especially insidious and contain potent toxins that result in HABs. During an HAB the toxins from poisonous algae pigment the waters and ultimately contaminate a particular planktonic community. As Donald M. Anderson, a senior scientist at the Woods Hole Oceanographic Institution, describes it, “red tides often occur when heating or freshwater runoff creates a stratified surface layer above colder, nutrient-rich waters.”
Among the worst HAB offenders are members of a particularly eerie class of algae known as dinoflagellates. Not only do these tiny creatures photosynthesize and contain chlorophyll like plants, but they also bear an animal-like characteristic – a long, undulating twin tail that propels them forward. Although scientists are uncertain about why, certain dinoflagellates prove lethal to higher organisms. Some devour their neighbors. In other instances, when fish break open the fragile blooms as they swim, toxins are released that are absorbed in fish’s gills, causing asphyxiation. Or creatures that feed upon the algae – clams, mussels, oysters, or scallops – retain the poisons in their tissues. “Typically the shellfish themselves are only marginally affected, Anderson has written, “but a single clam can sometimes accumulate enough toxin to kill a human being.”
Over the last decade the number of identified dinoflagellate species has risen from twenty-two to fifty-five in waters around the globe. Simultaneously, we are witnessing massive fish kills, such as that caused by the red tide that wiped out millions of menhaden last fall along the Texas coast and forced a ban on oyster harvesting. We are also seeing increasing incidences of human illness, especially in the underdeveloped world, where monitoring of HAB events is inadequate. In one example a toxin called ciguatera, produced by a dinoflagellate found in seaweeds, sediments, and coral rubble, enters the tissues of tropical fish such as the red grouper and dog snapper. An estimated ten thousand to fifty thousand seafood consumers worldwide are affected annually by ciguatera. More than 175 gastrointestinal, neurological, and cardiovascular symptoms have been recorded.
According to Dr. Ted Smayda, professor of oceanography at the University of Rhode Island and an expert on HABs, “the evidence suggests that these [HABs] are occurring where there has been increased nutrient enrichment of coastal waters.” In our world of multivitamins, “nutrient enrichment” may sound like a boon, but for underwater ecosystems it is a blight, occurring in an environment saturated with too-high levels of nitrogen and phosphorus – which are associated primarily with the runoff of human sewage, agricultural fertilizers, and animal waste. “We’ve made remarkable progress over the last twenty-five years in treating discharges from sewage and industrial polluters,” notes Tim Eichenberg of the Center for Marine Conservation (CMC), who cochairs with NRDC the Clean Water Network. “But during the same period we’ve done almost nothing about runoff.” As Beth Milliman of the Washington, D.C.-based Coast Alliance puts it, “Runoff is the last almost completely unregulated source of pollution into coastal waters.”
Take the phenomenon of the mysterious dinoflagellate called Pfiesteria, first detected in a North Carolina State University at Raleigh laboratory in 1988. The work of aquatic ecologist Dr. JoAnn Burkholder has since become the focus of a book And the Waters Turned to Blood. The title derives from a biblical passage in Exodus, describing the first of the ten plagues of Egypt and perhaps the earliest recorded instance of a red tide: “… and all the waters that were in the river were turned to blood. And the fish that were in the river died; and the river stank.”
|Florida Dept. of Natural Resources
The dinoflagellate responsible for red tide outbreaks, magnified 4,600 times.
Burkholder eventually identified the new Pfiesteria microbe as the culprit in the largest fish kill in North Carolina history – nearly a billion menhaden baitfish in 1991 in Pamlico Sound. While menhaden are not harvested for eating, they are a key forage species for larger fish like the striped bass and are used in the production of oil and fertilizer. Pfiesteria, Burkholder found, could lie dormant at the bottom of an estuary for years before suddenly, inexplicably springing to life. The catalyst is a still-unidentified chemical signal given off by passing fish, which stimulates the microbe. “Pfiesteria can transform from an amoeba to a toxic zoospore in two minutes,” Burkholder has said. “The zoospores make toxins that are shed into the water, basically drugging the fish and making them lethargic. The toxins can rip a hole through the skin of the fish, causing bleeding sores, although some fish die so quickly that no sores develop”
Until last summer the majority of fish kills attributed to Pfiesteria had been confined to North Carolina, mainly in its lower Neuse River. Then it spread to the Chesapeake Bay region, where several Maryland and Virginia rivers were closed to fishing for more than a month. Although menhaden that move through the tributaries in large schools were the primary species affected, there are also concerns about long-term problems for striped bass (known as rockfish in their Chesapeake Bay spawning grounds). The Atlantic striper has only recently made a comeback after stringent regulations were placed on over fishing. “One effect observed in rockfish in Burkholder’s lab has been bleeding underneath the skin,” points out Kim Coble, senior scientist for the Chesapeake Bay Foundation. “That’s also a symptom prevalent in the bay’s rockfish, whose average body weight is down substantially.”
Not only has Pfiesteria invaded menhaden and perhaps rockfish, it also seems capable of making the species jump to humans. Back in 1993, Burkholder and a colleague suffered nausea, disorientation, and memory loss after inhaling fumes emanating from lab tanks of fish dying from Pfiesteria. When the same symptoms occurred in fifteen Chesapeake Bay fishermen in 1997, what some called Pfiesteria hysteria ensued. Four months after experiencing memory loss and other problems associated with Pfiesteria exposure, thirteen of the fifteen individuals had fully recovered. (Altogether, Maryland has seen thirty-seven Pfiesteria-related cases.) Scientists asserted that the toxic microbe posed no health hazard to fish consumers, but Maryland’s seafood sales plummeted as much as 75 percent in some regions. Congress appropriated $7 million for the federal Centers for Disease Control and Prevention to conduct an ongoing investigation of Pfiesteria in several states.
|Dr. Ronald Hedrick
Tubifex worms harbor the whirling disease parasite.
The sudden appearance of Pfiesteria coincided with a quadrupling of the North Carolina hog industry over the past decade. In the eastern part of the state almost 10 million hogs now produce the equivalent waste of all the people in New York State and California combined. Burkholder declared her belief that the growth and reproduction of Pfiesteria was being stimulated by excessive nutrient runoff. Twice in the summer of 1995, after she announced her discovery, Burkholder received anonymous threatening phone calls. “If I knew what was good for me, I would drop the research – only more bluntly than that,” she says.
“This waste is being stored in open cesspools – they call them lagoons – and hogs produce more than 200 million pounds of nitrogen per year,” according to Rick Dove, riverkeeper for the Neuse River, which flows for about 250 miles before emptying into the sea. “The U.S. Department of Agriculture [USDA] says between eighty and ninety percent of that nitrogen is discharged to the environment as ammonia gas. When it comes back to the ground, nature converts the ammonium to nitrates, basically fertilizing the river to death. The predominant winds move west to east, so it’s almost all moving into the Albemarle/Pamlico Sound and the ocean shores.” Early in 1997 the state declared a year-long moratorium on new hog farms in three counties drained by the Neuse River.
Along Maryland’s lower eastern shore, says Coble, “all the data we’ve seen makes it very clear that the primary source of nutrients is agricultural, specifically the application of manure. More than ninety percent of the soils are saturated with phosphorus.” Whereas the North Carolina source is the hog industry, in Maryland it is poultry. An estimated 111 million broiler chickens are raised annually in the Pocomoke River watershed, producing about one-quarter of a billion pounds of manure – twenty-five times more waste than that produced by the people living there. “There just isn’t anyplace to put it,” adds Coble. “A short-term issue that has to be investigated is transporting the manure to a composting facility, or another agricultural area that needs fertilization. We’re also calling for a moratorium on growth in that industry.”
Solutions are being sought. Last October, to reduce as much as 90 percent of the runoff, $200 million in federal funds were allocated to replace plowed fields with a buffer zone of trees along nearly all of the Chesapeake Bay waterways. This marked the first time that wetlands conservation and agricultural programs have merged in this fashion. The USDA will “rent” land from participating farmers, who will be paid by the state of Maryland to set aside permanently as many as twenty thousand acres. Vice President Al Gore, on hand for the announcement, said, “By protecting the lands adjacent to the tributaries of the bay and by restoring wetlands we can significantly reduce the amount of nutrients, sediment, and pesticides that reach the water.”
Gore also instructed federal agencies to come up with other programs to help control runoff, a problem that until now the twenty-five-year-old Clean Water Act has largely failed to address. “There are many existing tools within the Act to control factory-farm pollution,” says NRDC policy analyst Robbin Marks, “but it’s incredible how little regulation and enforcement has gone on.” She cites the fact that while there are roughly 6,600 factory farms in this country, only approximately 30 percent of them have obtained permits from the Environmental Protection Agency (EPA). Of those, virtually none are poultry farms, and only a minuscule number are hog farms. To enforce the permitting process on factory farms, the EPA is developing a new administrative strategy, and Congress is considering legislation.
Elsewhere the upsurge in HABs makes their Pfiesteria cousin pale by comparison. Along Florida’s west coast large expanses of coastline are being affected by red tides for periods as long as eighteen months. Scientists speculate that between ten and fifty miles offshore, in low-nutrient water, a torrent of nutrients is produced as the current surges against the continental shelf, propagating the algae. The red tide is then transported into nutrient-rich, shallow waters by winds and/or currents, where it continues to multiply to harmful levels. The result has been poisoned shellfish, dead and rotting fish on beaches, and toxic airborne irritants that drive residents and tourists from the shoreline.
Dead yellowtail flounder following a red tide in western Japan.
Woods Hole marine biologist Donald Anderson is quick to note that pollution cannot be blamed for all the HABs. “It’s a likely factor in some, but certainly not all, instances,” he says. “One cause is simply natural dispersal – currents, storms, and movement of water carrying cells from one area to another. This is what happened with New England’s first experience with a toxic red tide in 1972, after a hurricane. I believe most of the new outbreaks are naturally occurring and can be attributed to better scientific ability to detect toxins”
But many researchers, including University of Rhode Island’s Ted Smayda, beg to differ. While Smayda sees coastal runoff as a major contributing factor, he also points to such problems as the transoceanic displacement of exotic organisms through other means. They can be transported in ballast water or by attaching themselves to the hulls of ships. “Novel species, which are being introduced into many areas, sometimes go berserk and grow like hell if the habitat is suitable for them,” Smayda postulates.
Indeed, says Center for Marine Conservation water-quality scientist Jonathan Finney, “there have been more than two hundred species of introduced organisms in San Francisco Bay, some of which are wreaking havoc on the ecosystem” One of these is the Asian clam, first discovered there in 1986 and now the dominant bottom-feeding shellfish. “It seems to filter everything,” says Finney, “including nonharmful algal blooms that serve as the bottom of the food chain. People really don’t know what it will do to the fisheries there” The Asian clam also absorbs pollutants extremely rapidly, including selenium discharges from oil refineries. Highly toxic to wildlife, selenium was the culprit in the mid-1980s tragedy at the Kesterson Wildlife Refuge in California’s Central Valley, in which thousands of birds were deformed and killed. A study released by the U.S. Geological Service in March 1997 showed concentrations of selenium in the San Francisco Bay’s Asian clams to be several times higher than in native clam species. This in turn affects diving ducks, sturgeons, Dungeness crabs, and other wildlife that feed on Asian clams. Another study has found reproductive problems in ducks that migrate from northern California to Alaska, suggesting that they too may be ingesting higher levels of selenium.
Then there is the changing climate. While many researchers cite nutrient runoff, erosion, and waste dumping as the probable causes of new diseases that are ravaging coral reefs – where nearly one-third of the world’s fish species reside – Anderson views warmer waters as a likely key. Smayda agrees, citing the scientific argument that changing water temperatures induced by global warming will influence wind patterns, which in turn influence some of the sea-current or circulation patterns, which in turn influence how nutrients are pumped in or used in those systems – thus favoring more harmful algal blooms. “For example,” he says, “the El Nino episodes have resulted in the dispersal of a highly toxic organism from New Guinea into the Gulf of Thailand, in just over twenty years. In the process a lot of people became ill or died from eating contaminated shellfish;”
Fish and shellfish are not the only living creatures in the ocean subject to disease: coral is vulnerable too. “When the coral reefs go, the fisheries go, and there goes our food chain,” says Craig Quirolo, a Florida diver and founder of the conservation group Reef Relief. In the fall of 1996, along the only living coral reef in the continental United States, off Key West, Florida, Quirolo was the first to observe a mysterious epidemic that marine biologists have labeled white pox. Appearing as white blotches from the base to the tip of the coral, white pox melts the tissue and leaves behind the bleached skeletons of what had been living animals. In some areas of the reef their death toll was about 80 percent. “The problems are occurring at all depths, and the number of species affected is increasing,” says Dr. James Porter, a marine ecologist at the University of Georgia who has been studying the disease. White pox followed in the wake of earlier maladies called black band and white plague II. During the first eight months of 1997 another ailment, known as rapid-wasting disease, also destroyed vast coral patches along a two-thousand-mile swath from Mexico into the Caribbean.
As pollution and global climate change stir up trouble in the world’s waters, the rise in aquaculture – fish farming – may also be wreaking havoc. HABs appear to thrive on these captive audiences. “Often after a fish or shellfish farm is introduced somewhere, a year later the wild species nearby are dead from an HAB,” says Anderson. “The most likely explanation is that the toxic algae was always there, it just never had a bunch of caged fish for red tides to come up against and make themselves known.”
Viral diseases appear more prevalent in aquaculture too, particularly in the rapidly growing shrimp industry. As the domestic demand for shrimp has increased – it is our second-favorite seafood after canned tuna – U.S. harvests have not been able to produce shrimp fast enough. In 1996, $2.5 billion worth of shrimp were imported; most came from aquaculture operations in Asia and Latin America for processing at stateside facilities. Many of these shrimp were carrying a lethal disease, the Taura-syndrome virus. While its origins remain a mystery to scientists, the virus is named for the river in Ecuador where the first confirmed outbreak occurred, in mid-1992. It poses no health threat to people but turns shrimp tails a pinkish color and kills the shellfish within days. Once in a shrimp farm’s environment, the Taura virus, carried in gull droppings or airborne water bugs, or even on the wind, can spread rapidly. Within two years after its appearance, Taura syndrome had devastated shrimp farms all across Ecuador, Peru, and Brazil. It has since spread to both Central American coastlines, and by 1995 major losses were occur ring at U.S. farms, largely in Texas and South Carolina. According to the U.S. Marine Shrimp Farming Program, losses to disease (along with a lack of available feedstock) saw production fall from 6.6 million pounds in 1993 to a projected 1997 figure of less than 1.5 million pounds.
|Howard Glasgow and JoAnn Burkholder
Atlantic menhaden with open sores, infected with Pfiesteria.
“These outbreaks,” the National Marine Fisheries Service reported last year, “have raised concerns that viruses could spread from aquaculture facilities to the wild shrimp stocks in U.S. coastal waters with potentially serious implications…. Infected shrimp processed in the United States may infect wild shrimp via solid wastes, effluents, bait shrimp, and infected material from processing used in shrimp and fish feed ”
As a result of such outbreaks, shrimp farms in Texas are now required to obtain permits to monitor discharges of wastewater for evidence of the disease. Yet Diane Wilson of Seadrift, Texas, a shrimper and founder of the Calhoun County Resource Watch, notes that only two of the state’s fifty-two shrimp farms have obtained such permits. “It’s not even clear what state agency has control over the industry and who’s watching what,” she says. “It’s totally out of control. They should put a moratorium on shrimp farming.” Adds Deyaun Boudreaux, environmental director for the Texas Shrimp Association, “We’re skeptical that our coast is the appropriate place for this type of pond impoundment. The discharges from these farms are going right into our shrimp nurseries, during a life state when they’re most vulnerable.”
Even the isolated and pristine western trout streams, long known as a fly-fishing paradise, are not immune to disease. Specifically, they have been infected with whirling disease, so named because the culpable parasite deforms the trout’s cartilage and causes the fish to whirl in the water before it dies. The tubifex worms that host the parasite, says Barry Nehring, of the Colorado Division of Wildlife, “thrive anyplace in an aquatic ecosystem where there is accumulation of sediment and/or organic matter.” An article in the New York Times reported that the worms also increase “exponentially in polluting waters.” Scientists are currently examining whether warmer water temperatures cause the whirling-disease spore to spread and to what extent pollution erodes the trout’s immune system.
The arrival of whirling disease in the United States has been traced to a shipment of frozen trout fillets from Denmark back in 1956. Experts believe the disease first surfaced in Pennsylvania rivers in the late 1950s through the disposal of contaminated fish parts. It is thought to have eventually spread westward through the transport of hatchery-raised fish to Rocky Mountain trout farms. Scientists contend that for decades the parasite lay dormant but then mysteriously awakened. By the mid1990s, whirling disease reduced the numbers of rainbow trout in Montana’s Madison River to 10 percent of what they had been only four years earlier. A similar scenario has unfolded along almost two hundred miles of Colorado’s premier trout streams; twenty-two other states have reported incidences of trout infected with whirling disease.
A rainbow trout exhibits the characteristically deformed cartilage associated with whirling disease.
Nehring explains what transpired: “In the last two decades a huge proliferation of people have built their own trout-stocking ponds on rivers. Once an infected fish is released into the wild, that’s how the disease spreads. First the fish dies, and the spores from its decomposed body are ingested by aquatic worms, which in turn produce a waterborne version of the parasite that reinfects. It so happens that the spores released by the worms float downstream almost in perfect synchrony with the emergence from the gravel of young, recently hatched wild fish – at a time when they are most susceptible to severe damage.”
“This disease has put at risk one of the great treasures of this country,” says Patrick Graham, director of Montana’s Department of Fish, Wildlife and Parks. “And it has moved much faster than we had expected.” Colorado fisheries researcher Keith Thompson warns of a “biological Chernobyl” should the parasite’s presence continue to expand. Not only the rainbow trout, but the West’s cutthroat trout – a food source for many animals, including the threatened grizzly bear – is in grave jeopardy as well.
So much has transpired in such a short time that scientists have had little opportunity to react, much less develop a game plan. As Ted Smayda puts it, “There are so many concurrent changes going on in freshwater and marine habitats. We are seeing disease in all these different compartments, each of which may be responding to different types of modification in the overall environment. Whether you’re talking about nutrient enrichment, ballast water, climate change as a result of carbon dioxide, or fishing pressure, the anthropogenic signal is there.”
There may be as many solutions as there are diseases and sources. Lisa Speer, oceans specialist for NRDC, describes the overall situation: “We understand so little about what this flood of chemicals and other toxins into the water is doing. With runoff we’re seeing so many signs that really need to be addressed – and quickly. We ought to be adopting a position as we have with global warming: we don’t know for sure what all the linkages are between the danger signs, but let’s take much stricter action.” Science and government must work together to fund research and create solutions. But, as in waters clouded with algal blooms, our visibility is limited, our outlook is unclear, the direction we must take remains murky.
The incidences of new diseases among marine life from fish to shellfish to marine mammals – are be coming so widespread as to be mind-boggling. Here are a few examples from the last two years.
- In California, where abalones have long been over-fished, the industry generates nearly $4 million in annual sales, mostly to Asian buyers. But those numbers may be difficult to sustain. An international group of marine biologists warned that a tiny parasitic worm is infecting abalones in some of California’s commercial shellfish farms; just as shrimp-farm diseases have spread to the wild, this parasitic worm may infect the abalone’s natural environment. The worm was first noticed a decade ago in an abalone shipment from South America. It acts by weakening and deforming the abalone shell, slowing growth and reducing the meat. Last May the California Department of Fish and Game outlawed the transfer of any farm-related abalone into the open ocean. But according to National Fisherman magazine: “recent studies confirm that some growers still are dumping empty abalone shells, kelp, and other debris into the ocean, where the worms may reach wild stocks.”
- In 1997 a disease dubbed QPX was discovered among quahogs at clam farms in Massachusetts, Virginia, and New Jersey. Nobody knows what causes QPX to kill the quahogs just as they reach marketable size. [t, too, is considered a potential danger not only to .armed quahogs but also to those in the wild.
- Noting deformities in frogs – multiple and missing appendages and oddly deformed eyes – in the United States and Canada, scientists studied samples of water drawn from Minnesota ponds where the frogs had been seen. Last October, at a conference in France, the researchers announced that an unknown water-borne agent is the most likely cause of the deformities.
- Following the release in March 1997 by the U.S. Army Corps of Engineers of more than 3 trillion gallons of polluted Mississippi River water through a spillway, an algal species called anabena caused fish kills and prompted health advisories at Louisiana’s Lake Pontchartrain. The freshwater was carrying high amounts of nutrients from runoff along the Mississippi watershed, which drains 41 percent of the lower forty-eight states. In June fishermen and boat operators were urged to stay off the lake. It was thought the organisms would die off by autumn; Lake Pontchartrain has yet to recover.
- In mid-September 1996 tens of thousands of dead fish – herring, red snapper, speckled trout, red drum, saltwater catfish, and more – washed ashore on Mustang Island near Texas’s Gulf Coast. Scientists noted that the apparent cause, a red tide, may have developed after heavy rains (following an extended drought) poured nutrient-overloaded freshwater into the surrounding sea waters.
- Sea turtles all over the world have been seen covered with noncancerous growths called fibropapillomas, which eventually smother the animals. In some habitats the infection rate is as high as 90 percent, especially in near-shore areas.
– Dick Russell