This could be a landmark event, especially for the people living in the Caribbean who have found Sargassum taking over their beloved beaches. Sargassum is a type of brown seaweed with berrylike air-filled bulbs. These gas-filled bladders are known as pneumatocysts and provide buoyancy to the plant. This is why sargassum forms in masses and floats (think “Sargasso Sea”) and therefore why it easily invades the beach in large quantities.