Nutrient runoff from rainfall has led to record concentrations of algae in the Chesapeake Bay and extensive dinoflagellate blooms, according to researchers at the University of Maryland System and the Benedict Estuarine Research Laboratory.
Dinoflagellates are a particular worry, according to scientists, since some species are known to cause toxic "red tide" blooms which kill fish and other marine life. "We have been fortunate so far in the Chesapeake Bay," according to Gail Mackiernan, assistant director of the Maryland Sea Grant College, "since there appear to have been no extensive fish kills from toxic dinoflagellates -- as there have been in North Carolina and Florida, for example. Most of the Bay's problems with phytoplankton blooms occur when the algae die, sink into deeper water and decay, causing a precipitous drop in oxygen levels." However, she cautions that toxic blooms are not impossible as some problem species have been identified from the Bay.
Visible only with the aid of a microscope (except when collected together in a dense bloom), dinoflagellates share characteristics of both plants and animals. Most carry chloroplasts, and can therefore perform photosynthesis like all plants; but they also exhibit behavior more typical of animal life, using a whip-like tail (flagellum) to move about _ and in some cases apparently to mount a swarming attack on hapless fish. Some species also feed on other microscopic creatures.
In North Carolina waters considerable attention has fallen on the so-called "phantom dinoflagellate," Pfiesteria piscicida, which has been blamed for numerous fish kills in the Neuse River and elsewhere. According to researcher JoAnn Burkholder at North Carolina State University, this microscopic algae can lie dormant in a cyst-like form for extended periods of time, can change shape rapidly and often, can swarm and attack schools of fish, and can release a powerful toxin that poisons and kills large numbers of fish very quickly. The dinoflagellates then feed on materials released by the dead and dying fish.
Although there have been no documented cases of fish kills caused by the phantom dinoflagellate in the Bay itself, scientists have kept a watchful eye because of the organism's potential to cause dramatic die-offs. In 1993, researcher Alan Lewitus, then working at the Horn Point Environmental Laboratory
(University of Maryland Center for Environmental and Estuarine Studies), isolated a dinoflagellate from Bay waters that appeared to be the toxic phantom. At about the same time, Denise Breitburg, a researcher at the Benedict Estuarine Research
Laboratory, lost a whole tank full of fish called gobies, a die-off she says was caused by the phantom dinoflagellate.
"We sent the samples to JoAnn Burkholder, who confirmed our suspicions," Breitburg says. At the end of August 1996 the insidious organism apparently struck again, and Breitburg and her colleagues witnessed another dramatic die-off in her laboratory. "We had about 100 juvenile fish (mummichugs) in a big tank," she says. "When we came in after the week-end, we had a pile of dead fish on the bottom --- all the fish were either dead or dying."
Breitburg and her colleagues identified the phantom dinoflagellate in the tank, but got confirmation from JoAnn Burkholder to be sure. "I don't know of anything else that kills so many fish so quickly," Breitburg says. "It [the phantom dinoflagellate] gets every single fish simultaneously."
She is hoping to avoid a repeat performance. "We've just spent two days scrubbing the lab with bleach," says Breitburg, who is being especially careful to make certain the dinoflagellate is eradicated from the laboratory.
Aquaculturists Not Immune,
Fish farmers may be no more immune to the ravages of dinoflagellates than Bay scientists or North Carolina fishermen. At least one Maryland aquaculturist has experienced serious losses this year, apparently as the result of dinoflagellate blooms.
"We knew we had an anomalous situation early in the season," says Tony Mazzaccaro, owner and operator of Hyrock farm, on the Manokin River near Princess Anne. The water seemed "awfully dark," says Mazzaccaro, and he thought there might be tannin in the water (an acidic solution often resulting from decaying leaves in wooded areas). All water quality measurements seemed okay --- but as it turns out, there were almost certainly dinoflagellates even then.
Nevertheless, the hybrid striped bass seemed healthy and continued to feed until mid-summer, when the fish took a sudden turn for the worse. "They went off their feed," Mazzaccaro says. And then they began to die.
By the time Sea Grant Extension specialist Dan Terlizzi was called in to look at the ponds the dinoflagellate bloom was thick. "One of the densest I've ever seen," says Terlizzi. With a simple microscope Terlizzi was able to identify dinoflagellates, but samples were sent to Wayne Coats of the Smithsonian Environmental Research Center in Edgewater, Maryland for more specific identification. Coats isolated a number of species of dinoflagellates, including what looked to be one of the life stages of the phantom dinoflagellate.
Coats sent a sample to Karen Steidinger of the Florida Marine Resources Institute for identification, and she agreed that they had found at least one of the life stages of Pfiesteria.
"I don't think it was Pfiesteria that killed the fish," says Mazzaccaro, who points out that other dinoflagellates (such as the nontoxic Gyrodinium) comprised almost the entire bloom identified in the analyzed samples. For another thing, he says, he was able to treat another pond of fish beginning to show similar signs of stress with potassium permanganate, which seemed to control the toxic bloom right away. He doesn't think control would have been that easy if it had been the phantom dinoflagellate. Exactly what happened is not yet clear, says Terlizzi, who notes that methods for dealing with organisms like Pfiesteria in aquaculture operations are still very much in their infancy. Whether caused by the phantom dinoflagellate or not, the die-off represents a major setback for what many consider a model aquaculture operation in Maryland. By the time the bloom ended, Mazzaccaro lost some 20,000 hybrid striped bass near market size.
A Bad Break
Until the recent die-off, Mazzaccaro's decision to draw water from the nearby Manokin River to raise hybrid stripers (rockfish) in excavated ponds had paid off. "Hybrid bass raised in salt water produce a better-tasting product," according to Mazzaccaro.
"In nine weeks I sold 120,000 pounds of fish last year --- sometimes 5 - 8,000 pounds a day," he says. Demand was so high that, according to Mazzaccaro, "I could have sold a quarter million pounds of fish last year."
According to Terlizzi, Mazzaccaro had encountered and addressed most of the major challenges that face fish farmers --- marketing difficulties, water quality problems, predators and other problems. But with the recent fish kill, Mazzaccaro must now consider how to deal with dinoflagellates.
"I've applied for a grant from the Maryland Industrial Partnerships (MIPS) program," says Mazzaccaro, "to work on the problem." The MIPS program partners emerging businesses with experts at the University of Maryland, College Park, experts such as Fred Wheaton, an authority in the field of aquacultural engineering. The key, Mazzaccaro thinks, will be to sterilize river water drawn for his ponds. "Right now we're looking at an ozone system," he says.
"This is not just my problem," adds Mazzaccaro. "Every aquaculturist who isn't sitting over an aquifer, in this region and all over the nation, will need to solve this problem." The future of any aquaculture operation that depends on using water from natural bays and rivers will be affected by our ability to solve this problem, he says.
Whether or not the dinoflagellates --- including the "phantom" dinoflagellate --- will continue to be a problem for aquaculturists remains to be seen. But according to Denise Breitburg, we should not be "at all surprised" to find the phantom dinoflagellate in the Chesapeake Bay.
"We have now experienced the effects of the dinoflagellate [Pfiesteria] in two separate locations on the Patuxent River," says Breitburg, "and with two different species [gobies and fundulus]."
"It's definitely in the Bay," she says, and since one of its traits is to lodge in the sediments, she says she doesn't know how we could ever get it out.
For additional information contact: Jack Greer, Maryland Sea Grant: 301-405-6376 Dan Terlizzi, Maryland Sea Grant Extension: 410-267-5660