A giant sargassum blob. Red tide killing fish. The demise of our coral reefs. It seems like the hits just keep coming. And it could have a long-term impact on boating’s future, sort of like what Mount Vesuvius did to urban renewal

What’s been dubbed the “Great Atlantic Sargassum Belt” is actually the world’s largest brown algae bloom. A 5,000-mile mat of sargassum is creeping toward Florida and the Caribbean, according to reports from the University of South Florida-St. Petersburg.

A 2019 study found that since 2011, sargassum mats have been increasing. More than 8,400 tons, the most ever recorded in a single day, once washed up on Galveston Island, Texas.

For the past seven years, USF researchers have been tracking the growing sargassum accumulation. Dr. Chuanmin Hu, USF College of Marine Science, calls it a belt now stretching from the coast of Africa to the Caribbean. What began as an anomaly in 2011 is now breaking records.

“We really want to understand why this is the new normal,” Hu said. “And what are the causes and what are the consequences? Before 2011, there was almost no seaweed in the tropical Atlantic or Caribbean Sea.”

Brian Barnes, an assistant professor at USF, told NBC News that the seaweed could affect shipping routes and trap smaller boats by fouling propellers and clogging water intakes.

“A continuous, single mat could be several miles long and 100 meters wide,” he said. “You don’t want to get inside if you drive a small boat.”

When the seaweed covers beaches and shallows, it rots and releases noxious gasses. More than 11,000 acute sargassum toxicity cases were reported in an eight-month span in Guadalupe and Martinique in the wake of a 2018 sargassum bloom.

Red Tide

Agricultural fertilizer runoff is the most common cause of both red tide and the hazardous algae blooms we’re seeing in our waterways.

Red tide has returned to parts of Florida’s Gulf Coast thanks in major part to Hurricane Ian, a Category 4 storm that slammed southwestern Florida last September. In 56 of the water samples taken by the Florida Fish and Wildlife Conservation Commission this week, medium to high concentrations of red tide were found. Some of the state’s pristine beaches have been littered with dead fish, and the water turned reddish-brown, causing throat irritation and breathing problems for anyone on or near the water.

The bacteria responsible for red tide is naturally present in the Gulf of Mexico. It’s typically dormant until fed by agricultural fertilizer runoff containing high amounts of phosphorus.

The runoff, primarily from sugar cane, livestock and farming operations in central Florida, pours through rivers and into coastal waters to cause the blooms. Hurricane Ian’s massive rainfall increased the flow of fertilizers, animal waste and nutrients.

The current red tide episode is not Florida’s worst. Between 2017 and 2018, red tide lasted nearly 19 months, killing more than 2,000 tons of marine life and permanently reducing the near-shore fishing opportunities — something to which I can attest.

Reef Decline

Algae are also having destructive effects on aquatic ecosystems, like Florida’s coral reefs. Blooms rapidly use up the oxygen in water, starving other marine life and producing harmful gasses and toxins that create “dead zones.” There’s a reported 8,000-square-mile dead zone in the central Gulf of Mexico from Mississippi River runoff.

In the case of sargassum mats, if they become too dense over reefs, they block sunlight to the water column, causing plants to die. There’s a reason coral reefs are known as the “rainforests of the sea.” Despite covering less than 1% of the ocean, they provide essential habitat for a 25% of all marine life — more than 1 million species.

Concern for coral reefs is very real. Without them, we lose much of our sport fishing, tourism, shoreline protection and more. Addressing the causes of harmful blooms of every kind should be a priority for everyone with a stake in the marine industry.