The unwelcome seaweed monster

Could a humble seaweed take over our towns and jeopardise life? If you live in a beachside town in Florida, USA, or are enjoying a vacation on the many islands in the Caribbean right now, chances are a seaweed is throwing a stench of rotten eggs. In the past few days, the crashing waves have been dumping tonnes of decaying Sargassum, a brown algal seaweed, on the beaches. Coastal towns are spending thousands of dollars cleaning up the stinky mess.

Using space-based satellites, scientists foresaw the arrival of the seaweed monster, slowly drifting on the Atlantic Ocean, about a month ago. It came from the Great Atlantic Sargassum Belt—the largest macro algae bloom in the world—found near the coast-less Sargasso Sea in the central Atlantic Ocean.

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The 2023 bloom, which is the biggest recorded so far, weighs about 5.5 million metric tonnes—as heavy as 55,000 blue whales! It stretches about 8,000 kilometres—all the way from West Africa to the Gulf of Mexico.

While Sargassum may be having a bad rap in recent years for the mess they create, thanks to all the nutrients our rivers carry to the sea, these algae are special. Unlike other seaweeds, mats of Sargassum float freely on the ocean surface and aren’t attached to rocks. Their many air-filled bladders keep them buoyant, and the ocean currents help them drift. Although these mats of seaweed are only a few metres deep, they are home to over 200 species of fish and invertebrates, including the Sargassum fish, which looks like the seaweed, and the Sargassum crab that swims. Mats of seaweed also act as a nursery for many sea turtles and other marine life forms. Isn't Sargassum awesome? It depends on who you ask!