The Gulf Coast of Florida has been suffering this summer from a disturbing phenomenon — an expanse of murky reddish-brown water that kills vast quantities of fish and other aquatic animals, and leaves the beaches littered with carcasses and reeking from the smell of decomposition.
The carnage is the result of a phenomenon called a red tide — an explosion of harmful algal blooms, or HABs, that occurs in ocean waters around the world. According to the National Oceanic and Atmospheric Administration, HABs occur when colonies of algae — the tiny organisms that can live in both fresh and salt water — grow out of control, while producing toxins that can kill fish and make shellfish unsafe to eat.
Florida Red Tide
While HABs have been reported at times in every U.S. coastal state, they occur nearly every summer along Florida's Gulf Coast. There, the species that most often causes the problem is Karenia brevis, a microscopic organism — each cell is no more than 45 micrometers (less than 0.0018 inches) in length — with a massive potential for destruction. To distinguish it from other varieties of red tide, K. brevis blooms are called Florida red tide.
As this Florida red tide primer from the Florida Fish and Wildlife Conservation Commission details, K. brevis is found in the waters off Florida year-round in concentrations of 1,000 cells or less per liter (33.8 ounces) of water. But in the summer and early fall, K. brevis can go crazy. This study by University of South Florida scientists, published in the scientific journal Sensors, describes a July 2014 bloom in which the algae multiplied to concentrations of up to 20 million per liter of water in some patches, and formed a bloom that spread over thousands of square miles of offshore water.
Red tides apparently have been happening along the Florida coast for a long time — Spanish explorers described finding massive fish kills in the 1500s, and the phenomenon was first scientifically documented in the 1840s. A massive Florida red tide event that started in November 1946 lasted roughly a year and killed an estimated 1 billion fish.
What Causes HABs?
What exactly causes Florida red tide events remains a little murky, though a study published by University of Miami scientists in the journal Harmful Algae in December 2015 suggests that it has to do with fluctuations in the position of the Loop Current, a flow of warm water that travels through the Gulf of Mexico.
Though red tide has gotten a lot of media coverage, it's unclear whether the blooms actually are getting any worse. Marine scientist Dr. Vince Lovko, manager of the Phytoplankton Ecology Program at Mote Marine Laboratory in Sarasota, and Hayley Rutger, Mote's content development manager, write jointly in an email, "It's hard to provide a simple answer about the long-term trends in red tide frequency, abundance of the algae, size of blooms throughout Florida's history or long-term trends in other features, because data collection has changed and improved so much over time."
Red tides do a lot of damage. According to the Florida Fish and Wildlife Conservation Commission, the toxins released by K. brevis cause massive die-offs of fish, invertebrates such as shrimp, sponges, sea urchins and crabs, and seabirds. The toxins can cause sea turtles to swim in circles and lose their coordination, so that they become stranded and die, and creatures as large as manatees succumb to the poison as well.
But people — particularly those with emphysema and asthma — also can be harmed by red tide, as coastal winds blow airborne toxins inland as far as a mile (1.6 kilometers), this red tide FAQ from Mote warns. They're advised to avoid red tide areas.
Can Red Tides Be Controlled?
Can something be done to stop red tides, or at least to control them? So far, nobody's come up with an answer.
"Karenia brevis occurs naturally in the Gulf of Mexico, and there is no tried-and-true way to completely remove the algae and its impacts without potentially harming Gulf ecosystems," Lovko and Rutger write. "However, we are studying smaller-scale control and mitigation methods that may benefit limited-area waterways, such as closed canals in red tide-affected coastal communities."
Researchers are exploring some possible methods for red tide mitigation, such as "living docks" covered with filter-feeding animals and ozonation equipment that could remove red tide from limited areas of water. The use of K. brevis-killing compounds from seaweed or other organisms that would act as parasites on them are other possible remedies being evaluated, Lovko and Rutger write.