Slurry Of Clay Used To Fight Against Florida's Deathly "Red Tide"


Tom Hale


Tom Hale

Senior Journalist

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist

Red tide.

The single-celled algae that cause "red tide" produce a potent neurotoxin that can kill marine life, including fish, shellfish, and marine mammals. Image credit: Jillian Cain Photography/

The past week, hundreds of tons of fish have died along the Florida coast due to “red tide,” a nasty blood-red cloud of microscopic algae that pump out potent toxins. In a bid to fight back against the bloom, scientists have recently deployed a novel strategy to kill the algae using clay.

Known as clay flocculation, the process simply involves spraying the water surface with a slurry of modified clay particles and seawater. The clay binds to the algae and eventually sinks to the seabed. Eventually, the cells and toxins become buried. Many of the algal cells will also rupture when they make contact with the modified clay and die.


Researchers from Woods Hole Oceanographic Institute (WHOI), Mote Marine Laboratory & Aquarium, and the University of Central Florida recently rolled out this method to the canals and coast of Florida as part of an ongoing initiative that’s seen clay flocculation deployed at 25 other sites. 

Florida red tides are caused by microscopic algae native to the Gulf of Mexico called Karenia brevis. The single-celled algae produce a potent neurotoxin that can cause respiratory illness and eye irritation in humans, as well as kill fish, shellfish, and marine mammals. 

Red tide
Spraying clay slurry in Florida as part of the new trial. Image courtesy of Bekah Horsley/Mote Marine Lab

The algal bloom occurs when a population of K. brevis undergoes a rapid explosion of growth, turning portions of the water a blood-red color. Red tides have often frequented the Gulf of Mexico, but they can be stimulated by fertilizer and sewage transporting abundant nutrients into the water. Furthermore, warming waters fuelled by climate change have driven an increase in red tides in recent years. 

As for this recent project in Florida, the researchers will be keeping a close eye on the situation, frequently taking water samples from both the treatment area and non-treated area to see if they can perfect this method of controlling the red tide.


"This is just the first of what we hope will be several upcoming trials of clay flocculation on active blooms in the wild," Dr Don Anderson, Senior Scientist at WHOI and Principal Investigator for this Initiative project, said in a statement

“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,” added Dr Anderson.

“In addition to cell abundance and toxin concentration, our team is evaluating phytoplankton community composition as well as multiple water quality measurements before, during and after the clay application to determine the success of cell and toxins removal as well as the impact on other water column parameters,” said Dr. Vince Lovko, Co-Principal Investigator and Senior Scientist at Mote.

 This Week in IFLScience

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  • tag
  • fish,

  • algae,

  • clay,

  • algal bloom,

  • red tide