Sargassum (Phaeophyceae) is a brown seaweed that has spread massively. A floating mass of seaweed stretching from the Gulf of Mexico to West Africa is now the biggest seaweed bloom in the world. The vast rafts of it keep sunlight from reaching coral reefs; as it decays, the seaweed releases noxious compounds that harm marine life.
Sargassum is harvested from Caribbean beaches and coasts.