The Sargassum Crisis: Toxic Seaweed Inundation of Puerto Rico's Coasts

Beginning around 2011, Puerto Rico — along with other Caribbean islands — began experiencing unprecedented influxes of sargassum, a brown seaweed that arrives in massive floating mats from the tropical Atlantic. While sargassum has always been part of the Atlantic ecosystem (the Sargasso Sea is named for it), the scale and frequency of recent arrivals have reached crisis proportions.

Scientists attribute the sargassum crisis to a combination of factors linked to climate change and human activity: rising ocean temperatures, altered ocean currents, and increased nutrient runoff from agricultural fertilizers and deforestation in the Amazon basin and West Africa. These conditions have fueled explosive growth of sargassum in a region scientists call the Great Atlantic Sargassum Belt, which can stretch from West Africa to the Gulf of Mexico.

When sargassum washes ashore in massive quantities, it creates multiple environmental and public health hazards. As the seaweed decomposes, it releases hydrogen sulfide (H2S) — a toxic gas that smells like rotten eggs and causes headaches, respiratory problems, and nausea. Coastal residents, hotel workers, and beachgoers are regularly exposed. Decomposing sargassum also leaches heavy metals including arsenic, which contaminate nearshore waters.

The ecological impact is severe. Thick mats of sargassum block sunlight from reaching seagrass beds and coral reefs, suffocating marine ecosystems. Sea turtle nesting beaches become inaccessible when buried under seaweed. Fish kills occur in waters depleted of oxygen by decomposing biomass.

For Puerto Rico's tourism-dependent economy, the sargassum crisis is an economic disaster. Beaches that normally attract visitors become unusable for weeks or months. Hotels report cancellations. Fishing communities cannot launch boats through the seaweed. The cost of mechanical removal runs into millions of dollars annually — money the island's austerity-constrained budget can barely afford.

The colonial dimension is clear: Puerto Rico lacks the fiscal autonomy to mount an adequate response, the political representation to demand federal resources, and the environmental regulatory authority to address the root causes. Climate change adaptation, which could help mitigate the crisis, requires investment that the PROMESA fiscal control board has deprioritized in favor of debt service. The sargassum crisis exemplifies how colonized territories bear disproportionate costs of global environmental crises they did not cause.