Scientist Worry ‘Brown Tide’ Will Feed the Red Tide

red tide

The Florida Fish and Wildlife Conservation Commission (FWC) released the latest report on the condition of the beaches due to the red tide that is plaguing the state. After a week of lower red tide concentrations, levels are on the rise again.

Manatee County reported a concentration that is between 5 and 25 percent higher than the first week of September 2018, when conditions had improved by over 25 percent.

The red tide is caused by the Karenia brevis algae bloom in the water. Medium levels of red tide have been measured in 13 samples taken off Manatee shores, according to the FWC.

Experts detected traces of Trichodesmium, which is a cyanobacterium in Sarasota and Manatee Counties. Scientists are concerned the Trichodesmium could merge with K. brevis to form a “brown tide” 10 miles offshore.

A chemist at Florida International University, Kathleen Rein, stated that a Trichodesmium bloom in the middle of the crisis of the red tide could be bad news. Trichodesmium is photosynthetic, like Karenia. It is believed that its growth is simulated by iron in Saharan dust. It fixes nitrogen and the fixed nitrogen is used by the Karenia brevis to grow.

According to the FWC, the brown tide is only being detected in offshore waters, although it can appear anywhere this time of year. It is practically an annual event that is believed to be fed by African dust blowing across the Atlantic.

Blooms can grow so large that they can be seen from space. Some of them produce toxins, but most are not typically harmful to marine life. Unless the brown and red tides merge.

Vincent Lovko, a Mote Marine scientist, said Trichodesmium is unique because it forms well offshore and pulls nitrogen from the air instead of from the water. Some strains can be toxic, but according to Lovko, there has never been a report of a toxic brown tide in the Gulf of Mexico.

The two tides do not necessarily merge, Lovko explains. The Trichodesmium bloom will die and the Karenia can use the nutrients released as the bloom degrades.

Trichodesmium is present on the surface, K. brevis lingers a meter under the water. The problem is when the surface bloom degrades and sinks into the red ride, it provides a food source for the red tide, extending its natural lifespan.

Trichodesmium blooms have been documented as far back as the 1700s, when Captain James Cook of the British Royal Navy wrote about them, according to the FWC. Sailors call the blooms “sea sawdust” because they look like sawdust floating on the water. Larger blooms look like oil slicks and change colors during its lifespan. When they are healthy, the blooms are brown. They turn pink or white as they are dying.

Officials believe that Tropical Storm Gordon created surface currents that shifted the red tide bloom in a northwestern direction.

In Sarasota, red tide levels are between 5 and 25 percent lower than the first week of September, however, the Florida Department of Health is Sarasota County has issued a no-swim advisory at Bird Key Park Beach and Caspersen Beach due to high levels of enterococcus bacteria.

In Lee County, the FWC sampled water from 34 beaches. Six of the beaches in the county have high levels of red tide, nine beaches have medium levels, and 19 either have a low red tide or they are clear.

The high red tide beaches are Sanibel Lighthouse, Osprey Way in Captiva, Coon Key, Lighthouse Beach, offshore on Redfish Pass, and offshore on Gasparilla Pass.

In Charlotte County, Stump Pass and Englewood Beach have high levels of red tide.

The FWC is not reporting any signs of red tide in Collier County. On Friday, Sept. 7, 2018, the people on Fort Myers Beach did not see any signs of red tide. Businesses that have been suffering are encouraging people to return.

“Come to the beach and take a look for yourself. You’re probably going to be surprised. It’s not as bad as you think. It’s way better,” according to Cherly Duff, and employee of Rudy’s Treasure Chest.

Scientist are not sure when the algae will dissipate, however, blooms generally hit their peak in September or October

By Jeanette Smith


NBC 2: These are the beaches that currently have high levels of red tide
Bradenton Herald: Is a super bloom on the way? Scientists worry a ‘brown tide’ will merge with red tide
Bradenton Herald: There’s more red tide in Manatee, FWC says. Tropical Storm Gordon could be to blame

Image Courtesy of Jonathan L’s Flickr Page – Creative Commons License