Could Clay Kill Red Tide? Mote Scientists, Partners Think So

SARASOTA, FL — As red tide blooms take over the region’s bays and gulf waters, scientists at the Mote Marine Laboratory & Aquarium are leading an initiative to develop new tools to decrease the toxins that are harming marine life and causing respiratory irritation for those visiting local beaches.

Florida’s red tides occur naturally in the waters and are caused by a native species of algae, Karenia brevis. Karenia brevis produces brevetoxins that affect the central nervous system of fish and other vertebrates and can kill them, according to the Florida Fish and Wildlife Conservation Commission website. When waves break open the red tide organism's cells, it releases the toxins into the air, which can cause respiratory irritation, especially those with chronic respiratory conditions, like emphysema or asthma.

For two years, the Florida Red Tide Mitigation & Technology Development Initiative, a partnership between Mote and the Florida Fish and Wildlife Conservation Commission, has been working to battle red tide by developing new tools and technologies. More than 25 projects are already underway, according to a news release from Mote.

In one of the more promising projects, Mote scientists are working with the Woods Hole Oceanographic Institute and the University of Central Florida to explore the use of clay to kill red tide.

In response to the current red tide bloom affecting Sarasota Bay, Tampa Bay and the coastline from Sarasota to Pasco counties, researchers have been testing the ability clay dispersal to remove red tide cells and toxins from the water, a mitigation strategy used in other parts of the world to control other types of harmful algae blooms, Mote said.

This clay mitigation — a process known as clay flocculation — involves spraying the water’s surface with a slurry of modified clay particles and seawater. As the dense clay particles sink, they combine with red tide cells, which kills the cells and can bury them in the sediment on the seafloor, Mote said.

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Researchers recently began testing process in a Sarasota canal they were given access to by the city of Sarasota and the Sarasota Outboard Club.

The clay-and-seawater slurry was dispersed over the water using hoses. Then, a screen was placed into the water on one end of the canal, and water samples were taken on both sides to compare the treated and non-treated areas.

“Although we have many initiative projects in different stages of research and development, we’re excited to be able to conduct one of our first field tests to work through logistical hurdles and gauge the effectiveness of a treatment option in a real-world situation, with actual red tide present in a water system,” Kevin Claridge, vice president for Sponsored Research & Coastal Policy Programs at Mote and administrator for this initiative said.

Dr. Don Anderson, senior scientist at WHOI and principal investigator for this initiative project, added, "This is just the first of what we hope will be several upcoming trials of clay flocculation on active blooms in the wild. What we learn here will help us better understand how conditions in Florida affect its success and how clay flocculation might be tailored to blooms of Karenia brevis, as well as other species of algae, here and elsewhere in the world.”