Sargassum seaweed

Many marine species call the sargassum in the Sargasso Sea home. It is a wonderful ecosystem and an especially great place to grow up. Sargassum seaweed forms large mats that provide a perfect habitat for small fish and other creatures. This is a productive floating neighborhood surrounded by some of the clearest, cleanest ocean water in the world. The view from the sargassum mat must be spectacular, looking down at depths of 1500-7000 meters (5000-23,000 feet or 2.5-4.3 miles).

Sargassum seaweed is a brown macroalga and traditionally occurs in the middle of the Atlantic Ocean, trapped within rotating currents. This area is called the Sargassum Sea and is the only sea with no land borders. The gyre that contains the sea is caused by surrounding currents, including the North Atlantic Current to the north, the Gulf Stream to the west, the Canary Current to the east, and the North Atlantic Equatorial Current to the south. 

Sargassum seaweed is free to move around because it has no holdfasts (attachments to a substrate). This seaweed has many small gas bladders that make it float. This golden mass of seaweed forms a living ecosystem with a diverse community of organisms.

At least a hundred fish species, including mahi-mahi, over 140 species of invertebrates, and several species of sea turtles seek shelter and food among the haven of seaweed. In addition, many migratory seabird species rest on the surface of the mat during their long migrations. 

Endemic species are found only among the sargassum mats. The sargassum anglerfish is small and perfectly camouflaged. The sea slug called sargassum nudibranch resembles the gas bladders of the algae with its color and shape, grazing on hydroids and bryozoans that live in the seaweed. The sargassum crab is a tiny crab living in a sargassum universe and perfectly matches its color. The sargassum pipefish is a relative of the seahorse, sheltering vertically among the strands of seaweed. Endemic shrimp are there too, with a transparent, brownish-green color, found nowhere else in the world. 

At least five species of sea turtles use the floating seaweed mat as a temporary home: loggerhead, green, Kemp’s ridley, hawksbill, and leatherback sea turtles. Baby turtles feed on tiny fish, crabs, and shrimp that also live in the algae. The mat forms vital feeding grounds and an oceanic nursery, protecting juveniles in their early stages of life. The thick vegetation creates shelter from birds overhead and predation from larger fish below. The algae also absorb heat from the sun and acts like a warm blanket keeping the small sea turtles warm.

Once a world completely isolated and remote, the Sargasso sea has now morphed and broken off into a new entity. In 2009-2010, a massive amount of sargassum seaweed was pushed out of the Sargasso Sea by an intense negative phase of the Atlantic Oscillation, which altered regional winds and ocean currents. This event formed the Great North Atlantic Sargassum Belt. This belt of seaweed now occurs worldwide from West Africa, the Caribbean Sea, and the Gulf of Mexico. The sargassum seaweed flourishes seasonally, unfortunately landing on tropical beaches in the summers. This excessive biomass is causing problems for tourism, smothering coral reefs, posing a marine hazard to sea life, and producing toxic gases as it rots on beaches. 

Sargassum seaweed is causing massive disruption to many places.

Some places where this occurs are finding ways to use the sargassum weed. Seaweed can be made into very strong bricks for construction, and biofuels like biomethane.

Because the seaweed floats around in the Atlantic Ocean, it accumulates heavy metals such as lead, cadmium, and the toxic metalloid arsenic. Therefore, the seaweed is proving unfit for commercial use in cosmetics, as a fertilizer for crops, or as animal feed. Heavy metals are transferred from our polluted ocean waters to the algae. Hopefully, other uses are still viable.