Is a super bloom on the way? Scientists worry a ‘brown tide’ will merge with red tide

The Florida Fish and Wildlife Conservation Commission is reporting an outbreak of Trichodesmium, sometimes called a brown tide, in waters offshore of Manatee County.

It is a separate species but similar to the well documented Karenia brevis, a photosynthetic organism responsible for the persistent red tide hitting Manatee and other nearby counties along 130 miles of coastline. Concerns are now being raised that if the two blooms merge, it could essentially deepen an ongoing red tide.

Kathleen Rein, a chemist at Florida International University, said a Trichodesmium bloom in the midst of the ongoing red tide crisis could be “very bad news.”

While unable to address the size, location or movement as of Thursday, Rein said, “I can tell you that Trichodesmium is a cyanobacteria. It is photosynthetic, like Karenia. Its growth is believed to be simulated by iron in Saharan dust. It fixes nitrogen, then the fixed nitrogen can be used by Karenia brevis to help it grow. Let’s hope the two blooms don’t find each other.”

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So far, FWC is only reporting that the brown tide is being detected in offshore waters, though it can appear anywhere this time of year. It is virtually an annual event believed to be fed by African dust blowing across the Atlantic. Blooms can get so big that they can be seen from space and while some can produce toxins, they are typically not harmful to marine life on their own.

Unless the brown tide merges with red tide and essentially becomes a red tide’s food source.

Mote Marine scientist Vincent Lovko said Trichodesmium is unique in that it forms well offshore and instead of getting nutrients from the water, pulls nitrogen from the air. While some strains can be toxic, Lovko said there has never been a reported toxic brown bloom in the Gulf of Mexico.

“It’s a completely different organism from the marine dinoflagellate, Karenia brevis, which causes our Florida red tide,” Lovko said.

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So if the two blooms do merge?

“As the Trichodesmium bloom dies and degrades, Karenia can potentially use the nutrients that are released,” Lovko said, while noting it’s not necessarily a merge.

Lovko said Trichodesmium is more present on the surface than K brevis, which lingers about a meter under the water. The problem is when the surface bloom starts to die and sinks into the red tide, it can provide a food source to the red tide, potentially extending its natural lifespan.

According to the FWC, documented Trichodesmium blooms date back as far as the 1700s when Captain James Cook of the British Royal Navy wrote about them. Sailors call the blooms “sea sawdust” because small blooms look like sawdust floating on top of the water. Larger blooms can look like oil slicks and change colors during its lifespan from a healthy brown to a dying pink or white.