"FIPR came through with funding for this research at a time when the work was absolutely needed. Basic research had been done, but we needed to know more about the practical applications - what we could do about red tide. Water resource managers, the government, the people all wanted to know, but no one wanted to fund it because bloom control was controversial."

Dr. Mario Sengco
Woods Hole Oceanographic Institute
On: FIPR helping to understand how phosphatic clay may help stem red tide

Red Tide has been a recurrent and serious problem along the west coast of Florida for many years. In addition to massive fish kills that litter the beaches with dead and rotten fish, as well as frequent closure of shell fish beds, the microscopic organism, Karenia brevis, that causes red tide has killed manatees, dolphins, and seabirds. The toxin produced by this organism, called brevetoxin, can also cause respiratory problems among those living near or visiting the beach. Estimates of Florida red tide vary considerably, but costs of $20 million dollars for episodes that last several months are often cited. Scientists are working on ways of stopping red tide. A recently completed Florida Institute of Phosphate Research funded project has produced data needed to justify field testing of one possible solution: using Florida phosphatic clay to stem red tide.

Clay has been used in Japan, China and Korea to control or suppress red tide blooms. South Korea, according to Dr. Mario Sengco, who is working on the Woods Hole Oceanographic Institution phosphatic clay project, has done the most with the idea of using clay to control red tides to protect that country's extensive marine mariculture industry. In that part of the world, Sengco said, red tide is a major economic problem because people eat, and make their living harvesting and selling, fish and shellfish.

When added to the seawater, the clay particles attaches to each other and to microscopic organisms like the red tide algae, eventually growing into aggregate particles that settle to the ocean bottom. If they settle deep enough and are not resuspended or don't escape, the organisms die. Studies done in Korea also indicate that the clay does not build up on the ocean floor, Sengco said, but that may not be the case in other locations.

The Woods Hole study indicates that Florida phosphatic clay works better than other clays against the red tide, Karenia brevis because it is very fine and stays in the water for a long time. It also has a high concentration of a mineral (i.e., montmorillonite) that is very sticky and key to the clay's ability to capture a number of the algae organisms. Phosphatic clay also works well with red tide organisms (Heterosigma akashiwo) in Seattle, Washington's Puget Sound .

Phosphatic clay is produced as part of Florida's phosphate mining operations. The matrix that is mined contains roughly equal parts of phosphate, sand and clay. The clay and sand are separated from the phosphate, which is chemically converted into phosphoric acid and used mainly to make fertilizer. The clay is stored in settling areas that take up to 40 percent of the land that is mined. Settling areas crust within 3 - 5 years, but remain the consistency of pudding beneath the surface for a long time. While the soil is nutrient rich, the settling areas have limited use because of their load bearing capacity. Finding ways to reduce the amount of clay produced and stored and finding uses for the clay and settling areas that exist is a FIPR research priority.

FIPR's part of the Woods Hole study is complete and a final report has been prepared, but the findings are already being tested at the next level with federal funding from the National Oceanic and Atmospheric Administration (NOAA) and the Ecology and Oceanography of Harmful Algae Bloom (ECOHAB) program. This phase of the Woods Hole work is a field study of using Florida's phosphatic clay during a red tide event in Sarasota Bay. The field test is very tightly controlled, according to Sengco. In November 2003 the research team sprayed 1000 kg of phosphatic clay from a Florida phosphate mine into the bay and studied where it went and the impact on the bay bottom. The impact of the clay alone appears to be limited, Sengco said. This fall (2004) the team will test whether the clay can stem a red tide event in a small section of the bay. He said the hope is that the field test will demonstrate if the clay will work in the presence of strong currents and wind and whether the red tide that sinks with the clay will have an impact on the bay bottom.

Whether the concept proves to be useful to stem widespread red tide or is best used in targeted areas such as fish hatcheries, the data that the research is generating will be useful to environmentalists, water managers, regulators, legislators and everyone interested in finding answers to red tide, Sengco said.

"For years scientists have studied what causes red tide, the timing of red tide, what controls the algae blooms. But, every time they were asked what can be done about red tide, everyone threw up their hands and said 'we don't know enough'," Sengco said. "We are now in the position to say what can be done and once the data is complete and out there everyone else can look at it and decide whether this approach is feasible and environmentally acceptable."