Historically confined to the nutrient-poor waters of the Sargasso Sea, sargassum is thriving in new waters due to land-based nutrient inputs, climate variability, and river outflows. Remote sensing and field studies show that nutrient-rich discharges from the Mississippi, Atchafalaya, and Amazon Rivers are accelerating growth. Laboratory experiments demonstrate that the two main species—Sargassum natans and Sargassum fluitans—can double biomass in just 11 days under enriched conditions.
“By examining shifts in nutrient composition—particularly nitrogen, phosphorus, and carbon—we’re beginning to understand the larger environmental forces at play,” said Brian Lapointe, Ph.D., research professor at FAU Harbor Branch, in the September release.
Between the 1980s and 2020s, nitrogen levels in sargassum tissue rose by more than 50% while phosphorus slightly declined, raising the N:P ratio and signaling a strong connection to fertilizer runoff, wastewater discharge, and atmospheric deposition.
The spread of the GASB has reshaped ecosystems and economies across the Atlantic basin. Massive mats of seaweed smother beaches, disrupt fisheries, and strain coastal tourism economies from the Caribbean to Florida. In 1991, a biomass surge even forced the shutdown of a Florida nuclear power plant due to clogged intake pipes.
Lapointe noted, “The expansion of sargassum isn’t just an ecological curiosity—it has real impacts on coastal communities. The massive blooms can clog beaches, affect fisheries and tourism, and pose health risks.”
The FAU review also highlights micro-scale nutrient recycling, where organisms and microbes within sargassum mats help sustain productivity even in nutrient-poor waters. This reinforces the importance of considering both land-sea nutrient flows and in-situ ecological processes.
The 2009–2010 negative phase of the North Atlantic Oscillation may have seeded the GASB by shifting surface waters southward, allowing sargassum populations to expand into the tropics. Coupled with stronger Amazon flood cycles, these dynamics illustrate the tight feedback loop between atmospheric events, terrestrial runoff, and marine ecosystems.
A recent Nature Communications study underscores that these blooms are part of a wider trend: warming oceans and shifting circulation patterns are driving new ecological regimes across the tropics. FAU’s review connects these broad climate drivers directly to coastal impacts, highlighting the urgent need for international monitoring and adaptive management.
The research was supported by the Florida Department of Emergency Management, U.S. EPA, NOAA programs, NASA, and other partners. Authors stress that coordinated, basin-wide monitoring is essential to mitigate ecological damage and economic disruption from future blooms.
