Consistent genetic divergence observed among pelagic Sargassum morphotypes in the western North Atlantic

International audienceSargassum (class: Phaeophyceae, order: Fucales) is a complex group of marine brown macroalgae. There are 361 accepted species, mostly benthic, distributed globally in temperate and tropical waters (Guiry & Guiry, 2021). Among these, however, the world's only holopelagic macroalgae are as follows: Sargassum fluitans and S. natans. These drifters are suspected to reproduce asexually, maintain buoyancy via gas-filled floats, and establish a surface ocean habitat in the subtropical North Atlantic, equatorial Atlantic, Caribbean Sea, and Gulf of Mexico that is unparalleled in the open ocean. Individual, radial branching clumps are dispersed across the sea surface, aggregated by helical Langmuir circulation into parallel windrows, or concentrated into dense mats measuring 10s of meters acros