New space images reveal a previously unknown structure stretching almost 5,000 miles across in the Atlantic Ocean

Scientists detected 37.5 million tons of Sargassum brown seaweed drifting between the western coast of Africa and the Gulf of Mexico in May, according to researchers at the Harbor Branch Oceanographic Institute at Florida Atlantic University (FAU). This biomass has evolved from a regional presence in the Sargasso Sea into the Great Atlantic Sargassum Belt, driven by land-based nutrient pollution and ocean circulation, according to a study published in Science titled ‘Harmful Algae’.

How does Sargassum impact coastal economies?

The seaweed creates significant economic losses for regions dependent on tourism. Visitors often find foul-smelling shorelines and beaches that are difficult to access, according to the FAU study.

Local authorities must allocate substantial labor and financial resources to continuous beach cleanup efforts. Brian Lapointe, Ph.D., lead author of the study and research professor at FAU Harbor Branch, noted that nutrient-rich waters have previously caused mass strandings and costly cleanups.

The economic disruption extends beyond tourism. Lapointe stated that massive blooms can affect fisheries and previously led to the emergency shutdown of a Florida nuclear power plant in 1991.

What is fueling the growth of the Great Atlantic Sargassum Belt?

The expansion is linked to a shift in nutrient sources. According to Lapointe, the algae are moving away from natural oceanic sources like vertical mixing and toward land-based inputs, including wastewater discharge, agricultural runoff, and atmospheric deposition.

Early growth was fueled by nutrients originating from the Amazon River, according to the study. Researchers identified increases in carbon, nitrogen, and phosphorus levels within the sargassum tissue over time.

Satellite observations and ocean circulation models show the seaweed moves from nutrient-rich coastal waters, particularly in the western Gulf of Mexico, into the open ocean via the Gulf Stream and the Loop Current.

What are the environmental and health risks?

While Sargassum provides a habitat for marine species in the open sea, it becomes a hazard upon reaching the shore. Decomposing seaweed releases hydrogen sulfide, a toxic gas, according to the FAU research.

Large accumulations can smother beaches and damage coral reefs. These masses also create low-oxygen zones that disrupt coastal ecosystems, according to the study.

What may happen next for the North Atlantic?

The blooms may become a permanent annual event if land-based nutrient pollution continues to fuel biomass growth. Coastal communities could face increasing costs for beach maintenance and infrastructure protection.

Further shifts in nutrient composition may likely alter the stoichiometry of marine primary producers. This could potentially lead to more frequent mass strandings along the Gulf Coast and Caribbean beaches.

Frequently Asked Questions

What is Sargassum?
Sargassum is a genus of brown macroalgae that drifts freely across the ocean, providing marine habitats offshore but becoming a nuisance when it washes ashore.

Why has the amount of seaweed increased?
According to Brian Lapointe, the increase is driven by land-based nutrient inputs such as agricultural runoff and wastewater discharge, rather than natural oceanic mixing.

What health risks are associated with these blooms?
As the seaweed decomposes on land, it can release hydrogen sulfide, which is a toxic gas associated with decaying organic matter.

How should coastal cities balance tourism revenue with the rising cost of seaweed removal?