Pfiesteria is latest of microorganisms to infest waters Tiny creatures increasingly cause harm to fish, humans

September 18, 1997|By Timothy B. Wheeler | Timothy B. Wheeler,SUN STAFF

Red tides in Florida. Brown tides in Texas and Long Island. From Maine to Alaska, America's coasts are awash in tiny organisms that without warning can turn the water the color of mahogany -- or blood. Some of them also can kill fish and even unsuspecting human consumers of poisoned seafood.

Pfiesteria piscicida, the toxic dinoflagellate linked this summer with fish kills or lesions in three Chesapeake Bay tributaries, is the latest of a nasty bunch of microscopic creatures that have been increasingly wreaking havoc in recent years among fishermen and shore dwellers in this country and abroad.

"We consider this a national concern," said Kevin G. Sellner, director of a federal research program working to predict red tides and other "harmful algal blooms," as scientists call this coastal nuisance.

Invisible when present in small numbers, certain types of algae release potent toxins that can kill fish, birds and even marine mammals if the microscopic plants multiply into massive floating "blooms" or growths. Last year, along Florida's southwest coast, more than 150 endangered manatees died from a poison released by a red tide.

The impact on humans' health can be just as disastrous. Some blooms produce toxins that, when consumed in tainted fish or shellfish, can act on the nervous system, causing paralysis or memory loss. Others trigger bouts of severe diarrhea.

Airborne, cough-inducing toxins blown ashore from red tides have emptied resort beaches, and shellfish beds have had to be closed to keep consumers from eating clams, oysters and scallops that have accumulated the algae poison. Fishing industries and tourist attractions in Florida and North Carolina, among other states, have lost tens of millions of dollars.

"Winds and tides carry them onshore, they make a mess, kill fish and cause respiratory problems in people over wide areas," said Donald F. Boesch, director of the University of Maryland's Center for Environmental Science. He headed a panel of scientists that studied the blooms and their consequences last year for the federal government.

In the Bible

Harmful algae blooms are not new. Red tides are mentioned in the Old Testament, and fossils have been found in prehistoric sea beds. In this country, 16th century Spanish explorers reported Indian tales of fish kills in Tampa Bay during red tides.

The vast majority of microscopic plants and animals in oceans' plankton soup are harmless. Of some 4,400 algae species, about 50 or 60 are capable of producing toxins. Even those do not do so with any regularity. Many of them, like Pfiesteria, are 'u dinoflagellates, single-celled organisms so named because of the tiny whip-like appendages that propel them through the water.

The number of species known to cause problems has grown in recent years, and many researchers believe the destructive blooms likewise have been increasing in number and intensity.

"They are truly getting worse in many areas of the world, including the United States," said Donald M. Anderson, senior scientist at Woods Hole Oceanographic Institution in Massachusetts.

Blooms threaten virtually every coastal state, cover longer stretches of shoreline and involve more species, experts say. They also afflict inshore waters in Europe, Asia, Australia and South America.

Why they may be worsening, and what triggers them, is a mystery being hotly debated by scientists.

Some of the harmful blooms may be a manifestation of too much enrichment of coastal seas with nutrients from sewage and polluted runoff.

But Anderson, one of the world's leading researchers on harmful algae, says that "for most of the species in this country that are harmful, the link to pollution is weak at best. Many of them are growing in waters that are quite clean."

The red tides that affect Florida begin off the coast. But Maryland's Boesch says there are some indications the blooms of the toxic dinoflagellate, Gymnodinium breve, may worsen when they drift inshore where waters are nutrient-enriched.

Other scientists speculate that the early stages of global warming may be helping spread these organisms, expanding the range of waters they find hospitable. Still others suggest harmful algae may get more direct help moving around the globe, hitchhiking in water taken on as ballast by ships and then discharged in distant ports.

Whatever the cause, the outbreaks of harmful algae are unpredictable. Some are infrequent and limited to a small area, while others occur for several years in a row and cover thousands of square miles. Some blooms are so thick they discolor the water, while others may not be visible to the naked eye, masking the potent toxins being released.

"One area will have a bad [outbreak] one year, and another year another area," noted Woods Hole's Anderson.

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