Giant Seaweed Blob Carrying Harmful Algal Bloom Heads Toward Florida Coast

Sun seekers gather at Clearwater Beach in Clearwater, Fla, on July 4, 2020. Drone Base/Reuters

A seaweed blob spanning 5,000 miles, nearly twice the width of the United States, is heading toward the Florida Gulf coast, with officials warning that the thick mat of algae poses environmental and health concerns as it approaches the shore.

Known as sargassum, the brown seaweed floats in open oceans, and is considered mostly harmless—while serving as a habitat for fish and crustaceans. Sargassum blooms are not a unique phenomenon, but the current one is noteworthy, mainly owing to its enormous scale: it is so big that it can be seen from space.

Another aspect that makes the giant blob currently heading for the Gulf of Mexico dangerous is the presence of harmful algal blooms  caused by the microscopic algae species Karenia brevis, commonly known as the “red tide.” The red tide can lead to respiratory illnesses and cause eye irritations, while killing marine life, according to the National Oceanic and Atmospheric Administration (NOAA).

“Over the next 36 hours, some beaches may experience a moderate to high risk of respiratory irritation from Karenia brevis (red tide) in Collier, Lee, Manatee, Pinellas, and Sarasota counties,” said the agency in a forecast on Tuesday. The red tide “is also present along the coast at concentrations that may cause respiratory irritation with onshore winds in Charlotte, Monroe and Pasco counties.”

When the seaweed mass hits the shoreline, the algae decomposition may lead to adverse health reactions from those residing in the region. “Rotting sargassum causes the production of hydrogen sulfide gas which smells like rotten eggs,” and the gas can “irritate the eyes, nose, and throat,” according to Florida Health (pdf).

“If you have asthma or other breathing illnesses, you will be more sensitive to hydrogen sulfide. You may have trouble breathing after you inhale it.” However, hydrogen sulfide levels in open air areas like beaches are not expected to have long-term health effects, and are not known to cause serious diseases like cancer.

Sargassum itself does not sting or cause rashes.  However, tiny sea creatures living within the sargassum bloom can cause skin irritations to beachgoers.

Besides this, the seaweed blob can result in detrimental effects on local ecosystems, as excessive algae growth takes over reef-building coral or prevents coral bleaching by blocking sunlight and reducing water temperatures.

Sargassum-Impacted Shores

Ocean currents are currently pushing the sargassum west, toward beaches across the Caribbean and the Gulf of Mexico.

Algae is already a problem on Florida’s Gulf Coast, where a red tide has caused dead fish to wash ashore, driving away tourists flocking to the area for the spring break. Beaches in the area could be surrounded by the incoming sargassum, and the situation has the potential to turn severe.

Coastal areas in part of Mexico were issued a warning earlier in the week to make preparations for up to three feet of sargassum build-up.

Accumulation of the algae material can lead to boats and other vessels getting ensnared, and block valves to power plants and desalination plants, along with disrupting marinas.

After a considerable amount of sargassum washed up on its shores last summer and impacted water production capabilities on St. Croix, the U.S. Virgin Islands declared a state of emergency. Maintenance efforts were increased to clear up debris affecting desalination plants and restore water production in the region.

“I want to assure St. Croix that we don’t anticipate any impact on public health from this annual invasion of sargassum in our waters, including the stench that we all, unfortunately, have learned to live with every summer,” Virgin Islands Governor Albert Bryan said at the time. “However, the seaweed overrunning our beaches also brings the potential for disruption to businesses and other negative financial impacts to our economy.

Taking Precautions

Sargassum is found abundantly in the ocean, according to NOAA. It consists of leafy appendages, branches, and berry-like structures. These round structures are filled with oxygen enabling the plant structure to stay afloat.

A wide range of marine life, from fishes and turtles to marine birds and shrimps, set up breeding grounds on the sargassum. At the end of its life, the seaweed blob loses its buoyancy and sinks to the ocean floor where it becomes part of the deep sea.

According to Florida Health guidelines, officials have instructed beachgoers to avoid touching or swimming near seaweed to prevent getting stung by organisms that live within the sargassum. Gloves are recommended when handling seaweed. People are warned to stay away in case of developing breathing problems. People suffering from asthmatic conditions are advised to limit their time on the beach.

When the harmful algal blooms of Karenia brevis are broken up by waves along the shore, a toxin that causes irritations is released into the air. It combines with sea spray and leads to eye and respiratory irritations, including coughing and itching, for beachgoers. The effects subside with reduced exposure but some people may have persistent ailments and should avoid visiting the affected regions, NOAA says.