Influx of Sargassum Seaweed Washing Ashore

Sargassum seaweed, above and below, has been inundating shorelines across the Virgin Islands.

There is an extended and unusual influx of seaweed on the territory’s shores, according to the Department of Planning and Natural Resources. The presence of this Sargassum seaweed is typical in Atlantic and Caribbean waters, but the amount and distribution this year is not typical for this region.

The floating mats of Sargassum seaweed originate from the Sargassum Sea, which is an area of around 2 million square miles of calm waters in the Atlantic Ocean stretching from the Caribbean to the Azores.

Prevailing wind, storms, and currents disperse the weed from this area, and it is a common annual summer occurrence along shores of the Gulf of Mexico. This seaweed is a floating species that reproduces asexually and does not require any connection to a land surface.

The Sargassum seaweed is an important oceanic habitat for marine organisms, particularly juvenile fish and sea turtles that use it to shelter from predators. It is also an essential source of food for many off shore species. The seaweed is important for the sport-fishing industry, as the floating mats attract big game fish.

The seaweed itself is high in nutrients, and provides important enrichment to nutrient-poor beaches when it washes up. It provides nutrients needed by beach vegetation that in turn helps to stabilize the beach from erosion.

The seaweed is non-toxic, but as it decays on land it produces a strong odor. The decay process can begin as the seaweed builds up into bays. Not much can be done while the seaweed is in the water, but when it comes ashore it can be cleaned up using rakes.

Any mechanical removal requires a permit from DPNR. The seaweed can be added to a compost pile or disposed of at the landfill, although it should not be added to plants directly as mulch.

For more information on the Sargassum seaweed call the Division of Fish and Wildlife at 775-6762 on St. Thomas.