Sargassum is a genus of brown seaweed that floats in massive mats across the ocean. While it provides a vital habitat for marine life in the open sea, it becomes a major environmental and economic problem when "Great Atlantic Sargassum Belts" wash ashore in massive quantities. When these mounds of seaweed rot on beaches, they release hydrogen sulfide gas, which smells like rotten eggs and can cause respiratory issues for tourists and locals. From an ecological standpoint, thick carpets of sargassum can block sunlight from reaching seagrass beds and coral reefs, effectively "smothering" them. It also creates a physical barrier that prevents sea turtle hatchlings from reaching the ocean and can entangle larger marine animals. For the tourism-dependent economies of the Caribbean and Florida, the "brown tide" is a financial disaster, requiring millions of dollars in cleanup costs and leading to massive hotel cancellations as pristine white-sand beaches are transformed into smelling, sludge-filled shorelines.