At a Glance
- Since November 2017, a 145-mile stretch of Florida's southwestern coast has been plagued by a deadly red tide.
- A bloom of a saltwater blue-green algae serves as fertilizer for the red tide.
- The stench has become so bad that lifeguards on area beaches have resorted to wearing gas masks.
A naturally occurring saltwater blue-green algae bloom is likely feeding Southwest Florida's deadly red tide but should not be called a brown tide as it has been widely reported recently in the media, a Florida algae scientist said.
Since last November, a 145-mile stretch of Florida's southwestern coast between Pinellas and Collier counties has been plagued by a deadly red tide caused by Karenia brevis. Thousands of marine animals and fish have died as a result of the toxic bloom, and humans have suffered from respiratory ailments and rashes.
The stench has become so bad in some areas that lifeguards have resorted to wearing gas masks.
A different type of naturally occurring algae first noticed in June off the coast of Florida — this time from the marine cyanobacterium Trichodesmium — has caused some confusion this week after media outlets referred to it as a brown tide and reported that should the two blooms merge, a super bloom could result.
Dr. Michael Parsons, professor of marine science at Florida Gulf Coast Universtiy, told weather.com the Trichodesmium bloom "shouldn’t be called brown tide because it causes confusion." A true brown tide is caused by an entirely different organism, Aureoumbra lagunensis.
"Trichodesmium and Aureoumbra are completely different organisms," Parsons said. "Trichodesmium is related to bacteria (prokaryotic) and forms filaments which stick together to form visible tufts in the water. Aureococcus is eukaryotic and blooms as small single cells."
Parsons said Trichodesmium, also known as saltwater blue-green algae, serves as fertilizer for the red tide. It is found worldwide in tropical and subtropical water and blooms every year in the Gulf of Mexico. The Florida Fish and Wildlife Conservation Commission (FWC) notes that in southwestern Florida, Trichodesmium blooms can extend for miles and are visible from space.
Many scientists, including Parsons, believe the Trichodesmium blooms are a precursor for the development of red tides.
Trichodesmium grows on the surface of the water and sucks nitrogen from the air. As it dies, it sinks and serves as fertilizer for the red tide, which typically blooms about 3 feet under the water's surface.
"Trichodesmium can fix nitrogen, which means it can absorb dissolved nitrogen gas from the water surface, and convert it into organic nitrogen. It basically makes its own fertilizer," Parson said. "The nitrogen that Trichodesmium fixes then becomes available to red tide – Trichodesmium fertilizes red tide. Without the Trichodesmium, there would not be enough nitrate or ammonium to support a red tide bloom."
Algae Blooms Explained
Although often mistakenly used interchangeably, red tides and blue-green algae blooms are very different and are caused by different types of bacteria.
Red tides (caused by Karenia brevis) and saltwater blue-green algae (caused by Trichodesmium) are both naturally occurring algae blooms that form in marine water. Freshwater blue-green algae blooms are caused by different types of cyanobacteria, or groups of photosynthetic bacteria.
According to the FWC, freshwater blue-green algae blooms originate from runoff containing human waste and fertilizers from nearby farms and neighborhoods. Nitrogen and phosphorus, as well as other nutrients in the polluted runoff, can act like fertilizer for the algae, creating large and long-lasting blooms.
Red tides, on the other hand, occur naturally, typically develop 10 to 40 miles offshore in Florida and are fed by Trichodesmium.
The Marine Laboratory and Aquarium notes that there is no direct link between nutrient pollution and the frequency or severity of red tides in Florida. However, when red tides move closer to shore, they are capable of using man-made nutrients from runoff for their growth.
If ingested, water contaminated with toxins found in red tides, brown tides and blue-green algae can cause nausea, vomiting and, in severe cases, acute liver failure, according to the FWC.
The Centers for Disease Control notes that coming in direct contact with the algae can result in a rash. Some research indicates a link between long-term inhalation of toxic algae fumes and neurological disorders like Parkinson’s and Lou Gehrig’s diseases.
