Seaweed, seaweed everywhere

Floating Sargassum seaweed species are spreading in the Atlantic Ocean Thanks to the gas vesicles that give the Sargassum genus its name, the open-ocean seaweed species S. natans and S. fluitans float freely in the ocean. On page 83 of this issue, Wang et al. (1) report that patches and lines of these seaweeds have grown and spread through the Caribbean and across the north equatorial Atlantic to the west coast of Africa and the Gulf of Guinea, forming what the authors call the great Atlantic Sargassum belt. Other species of Sargassum, such as S. muticum (2) and S. horneri (3), have also increased their range recently but are rooted and are probably being spread through shellfish shipments and ship ballast water. It is the freely floating species that are providing the major changes noted by Wang et al.