written by
Norman Hart
On a recent visit to Antigua & Barbuda I noticed several beaches around the island littered with sargassum weed which has been increasingly plaguing Caribbean coastlines. Sargassum is a genus of large brown seaweed (a type of algae) that floats in island-like masses and never attaches to the seafloor. Smaller fishes, such as filefishes and triggerfishes, reside in and among brown Sargassum. Researchers used a 19-year record of satellite data to study the Sargassum, which has bloomed every year from 2011 to now. In 2018, as seaweed piled up on beaches throughout the Caribbean, it began to rot. Already stinking and sulfurous, the thick layers began to attract insects and repel tourists. Lately a lot sargassum has grown in the ocean and washed ashore in unprecedented quantities. It prevents fishermen from getting into the water, and entangles their nets and propellers. It entangles sea turtles and dolphins, smothering seagrass meadows and coral reefs. Because of it Barbados has declared a national emergency. In normal years, sargassum is a blessing rather than a curse. Mats of it drift around the ocean, held afloat by gas-filled bladders that look like grapes. They accumulate in the North Atlantic, forming the Sargasso Sea—The fronds are a breeding site for American eels, a sanctuary for turtle hatchlings, and a haven for hundreds of other species, some of which live nowhere else. The Sargassum fish, for example, is a small, frog-faced predator whose body has adapted to perfectly mimic the seaweed. 
For some years now, islanders have learnt to use sargassum to fertilize their crops. They take advantage of the seaweed as a natural fertilizer and herbicide to improve the harvest of products such as corn, squash and beans. Certain species are also cultivated and cleaned for use as a herbal remedy. Many Chinese herbalists prescribe it powdered.   
Images courtesy of the Life on the Edge Exploration