Community-based monitoring reveals spatiotemporal variation of sargasso inundation levels and morphotype dominance across the Caribbean and South Florida

During the past decade, massive inundations of holopelagic Sargassum spp. (S. natans I, S. natans VIII, and S. fluitans III), commonly known as sargasso, have drastically affected beaches and coasts throughout the tropical Atlantic, leading to strong forecasting and monitoring efforts. This study aimed to characterize spatiotemporal variation in accumulation levels and morphotype composition of sargasso inundations. Community science initiatives can aid in monitoring sargasso regionally by locally collecting data on morphotype composition and accumulation level. A volunteer network compiled community-contributed photos from the "Sargassum Watch" Epicollect5 digital application. Florida and the Gulf coast showed less susceptibility to high accumulations than other subregions of the tropical Atlantic. S. fluitans III was the most frequently encountered morphotype, though the probability of encountering any of the three morphotypes depended on accumulation level. Despite differences in latitude, the 2021 season demonstrated similar 'peak' sargasso months between South Florida and Mexican Caribbean (May–July), though the intensity and duration of high-accumulation months differed. Much of these composition patterns and accumulation levels were likely related to the proximity of both regions to the Great Atlantic Sargassum Belt and dispersal through wind and water currents. Using community-collected data to outline quantitative trends and patterns in sargasso accumulation levels and composition, this study can be useful for future collaborations and syntheses with other forecasting and monitoring programs.