Mats of Sargassum macroalgae overruns the Caribbean and culprit of the power outage in Puerto Rico

There are multiple species of Sargassum, a type of macroalgae common in the tropical Atlantic. For centuries blooms of the harmful seaweed have floated in the open low nitrogen waters of the North Atlantic. Sargassum could not reproduce in the northern waters of the Atlantic in large amounts as it needs nitrogen to flourish. Fish excretions, upwelling, and chemical nitrogen processes in the atmosphere were the only source of nitrogen keeping the weed under control. As the world population explodes, human sewage and agricultural runoff have provided nitrogen to Atlantic waters. Fertilizer runoff became a huge problem and has increased 85% since 1985, according to a study. This living organism exploded starting around 2011 and now covers thousands of miles of open water from Africa to Mexico. The warming ocean is also a factor in the blooms.

The enormous bloom has been named the Great Atlantic Sargassum Belt, and it is wreaking havoc in Africa, the Caribbean, the Gulf of Mexico, and South Florida. It exists in lesser amounts in other areas such as coastal Texas and North Carolina. These blooms can create coastal toxic dead zones transforming their role from a nursery to species such as Mahi Mahi, amberjacks and, larvae of multiple ocean species such as crab, shrimp, and sea turtles. Their role in the open ocean is beneficial to the health of the sea. Still, now the macroalgae “represent a danger to the quality of water, air, and the oxygenation processes that make aspects of marine life possible. The chemistry of the emerging threat can be found here.