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Red tide could recede

A Woods Hole scientist leads research on suffocating the algae by spreading clay.

By HANNAH FAIRFIELD
THE New York Times

Every year, stretches of the U.S. coastline are attacked by poisonous enemies that massacre fish and shellfish, unnerving beach-goers and prompting scores of "no fishing" alerts.

But these assailants, actually harmful algae that mushroom into dense colonies known as red tides, may soon be deterred by a humble defender: clay.

Scientists are testing ways to use ordinary clay to smother the algae, which are single-celled creatures. Spread thinly over tainted ocean waters, the clay clumps as it falls through the water column, coating the cells and causing them to die on the sea floor.

The procedure has helped protect billion-dollar fishing industries in South Korea and Japan, and some scientists believe it can be used in the United States.

"Lots of research has been done on toxins and chemistry of harmful algal blooms but very little about control or mitigation," said Donald M. Anderson, a red tide expert at Woods Hole Oceanographic Institution who has been leading the research. "But people who live along the coasts are sick and tired of living with the danger."

The red tides consist mostly of several dozen different kinds of algae, and are often not red at all, but occur as brown, orange or green mats, or are sometimes nearly invisible. They are not literally tides either, but are carried toward shorelines by the tides.

In many cases, the microscopic killers are algae in the form of dinoflagellates, single-celled creatures that can photosynthesize but can also propel themselves through the water with a long tail. In the last two decades, they have occurred with increasing frequency in the United States, most often in the late summer. Some scientists fear that fertilizers and other nutrients washing into coastal waters from land can trigger growth of some dinoflagellates.

Millions of fish, shellfish and birds can be killed as the microscopic organisms move through coastal waters. The National Oceanic and Atmospheric Administration estimates that more than $1 billion could be lost in the next decade as a direct result of the blooms' assault on U.S. waters.

Danger to humans People exposed to the toxins can experience disorientation, nausea, vomiting, and respiratory and weakened immune response, in some cases even if they have only walked near the poisoned waters and been showered by the spray. Plants like eelgrass also succumb to the killer, reducing lush shoreline habitats to bare deserts.

In May, Anderson and other researchers who have spent years doing tests in tanks received an $870,000 grant from a government consortium headed by the oceanic administration's Coastal Oceans Program to design a full-scale pilot project to test the clay procedure on a natural bloom in Florida.

The method, which Korea credits with helping reduce red-tide fishing losses from $100 million in 1995 to $1 million in 1996, could ultimately protect valuable fishing industries in states like Washington, Maine, Louisiana and Texas that are frequently hit with red tides. Clay application might also protect coastal communities like those in Florida and California that lose millions of dollars when beaches close.

Small-scale experiments using the clay have been surprisingly successful. Mario Sengco, a member of Anderson's lab at Woods Hole, tested the clay in large outdoor tanks when a toxic bloom hit Corpus Christi Bay. Sengco filled the tanks with bay water, mixed clay with water into a thin slurry and sprayed a fine mist of the clay over the tanks with a garden hose. In two and a half hours, the clay in several tanks had removed about 70 percent of the toxic cells from the water.

To make the clay particles stick together, Sengco uses a tiny amount of the coagulant polyaluminum hydroxychloride, a chemical often added to drinking water. This increases the effectiveness of the sinking clay to strip algae from the water, allowing the procedure to work with far less clay than used in Asia.

Risk to shellfish Despite the success of removing the cells from the water, some scientists are concerned that dispersing clay might have some negative effects. Research done at Dalhousie University in Nova Scotia showed that large amounts of sediment repeatedly resuspended in the water could harm animals living on the sea floor, like clams. However, EPA scientists in Florida found that smaller amounts of clay didn't cause any harm to shrimp or minnows. The new grant includes money for new field experiments.

"In areas where resuspension occurs - with tidal activity, and any storm or wind-induced mixing of the water column - clams and other sensitive bivalve species will be strongly affected by the increased sediment load," said Marie-Claude Archambault, an oceanography graduate student at Dalhousie University.

Other scientists are concerned that all the algae cells may not die when they fall to the ocean floor, therefore shifting the death zone from the surface to the bottom.

Sandra Shumway, a marine ecologist at the University of Connecticut, notes that some species of algae cells can survive low quantities of clay application. She believes that the large amounts of clay used in Korea and Japan would not be allowed in this country.

"The United States cares a lot about the environment, and I'd be surprised if anyone will be allowed to spread that much clay on the sea floor," Shumway said. "Even if it's done just with aquaculture, there are organisms on the bottom that will be harmed."

Proceeding cautiously is necessary, Anderson said. "We might remove dissolved toxin with lower amounts of clay," he said. "This might lead to the strategy of treating a red tide without having to remove all of the cells."

Last summer, he worked with fishermen in Washington to see how the clay application might work at a fishery. Using a power washer like those used to clean sidewalks, Anderson spread a veil of clay over salmon cages and watched the fish react. They coughed initially, but after the clay settled in a few minutes, the fish were unharmed. The scientists monitored sediment deposition and reported that so little was spread over a large area that there was no noticeable increase on the sea floor.

Jack Rensel, a fishing industry consultant in the Puget Sound area who is continuing the experiments, said the clay mitigation could save the industry when coastal regions were surprised by an algae bloom.

"Fish in cages have nowhere to go when a toxic bloom hits," he said. "We have to look at ways to try and save them."