Korea and Japan have used clay sprays to control red tides for more than a decade, but Americans have been reluctant to adopt the technique because of water quality concerns. Now, researchers at the Woods Hole Oceanographic Institute have found that local clay can smother the harmful algae without harming the local shellfish. It’s working in Florida and in Texas, but what about New England? Will clambakes ever be safe again?

The ocean is full of algae, many of which are innocuous and lie at the base of the food chain. But some, like those associated with red tides, or harmful algal blooms, produce harmful neurotoxins. If a human eats the meat of a poisoned clam he can become disoriented and nauseated or even paralyzed.

But the impact of red tides on the fisheries and tourism industries can be larger than their health effects. Public health departments minimize the risk of human illness by monitoring toxin levels and issuing bans on seafood fishing and consumption. The bans can stretch on for months, devastating the seafood industry.

In 1997, a Pfiesteria outbreak off the coast of Maryland cost the seafood industry $43 million, and according to a New York Times article published this summer, the National Oceanic and Atmospheric Administration estimates that more than $1 billion could be lost over the next 10 years from the effects of harmful algae blooms. Clay sprays could slash that loss of revenue.

Mario Sengo, a post-doctorial researcher at Woods Hole Oceanographic Institute, has spent the better part of four years studying the effects of natural clay sprays on U.S. algae species. Most of his work has focused on algae that affect the coast of Florida and Texas, which are different from those that cause red tides in the northeast.

The Japanese have been using clay sprays to control harmful algae blooms since the late ’80s, said Sengo, but the U.S. didn’t become aware of the technique until the mid-’90s. Korea and China have also used clay sprays to mitigate the blooms and save local fisheries.

In 1996, the Korean aquaculture industry lost an estimated $100 million from fish mortalities during a particularly massive red tide. The following year, said Sengo, they sprayed clay in and around the aquaculture pens, resulting in the removal of more than 90 percent of the harmful microorganisms from the water columns and a reduction in losses to $1 million.

Clay sprays appear to be effective at keeping algae blooms under control, but Sengo said more rigorous experiments must be completed before Americans begin watering their aquaculture pens with clay slurries. Based on the Korean data, Sengo estimates that hundreds of tons of clay were spread over the ocean.

“It’s like moving a hill over the ocean,” he said. But his Florida studies suggest that by adjusting the spray technique and the type of clay, Americans may be able to use 40 times less clay than the Koreans.

Sengo’s results are only preliminary. He has yet to do a pilot study in open water, but has tested the clay in an artificial water column, which resembles a sock floating in the ocean, to see how the clay settles and which organisms it removes.

Remarkably, the clay has specificity for the harmful algae. “It doesn’t remove all living things,” he said, explaining that the cell’s characteristics determine if the clay sticks to it. Some cells swim more vigorously, while others are coated in mucous, but both are tactics that keep the cell from being coated in clay.

New England’s algae seem to be particularly feisty. Out of 25 clay types Sengo has tested, none are effective against Alexandrium tamarense, the primary species of harmful algae found in the northeast.

“The New England organism may just be very powerful swimmers or escape with some method we just don’t understand,” Sengo said.

Another problem lies in the potency of the New England variety.

“You can get toxicity with one to 100 cells per liter,” Sengo said. “In natural systems, there are so few microorganisms that I can’t see how you can justify using something like this to treat a small bay or estuary.”

The solution may lie in a combination of clays and flocculants, he said.

“It’s not a silver bullet that will cure the red tide,” Sengo said. “But it’s very interesting.”