LAUSR

The recent spread of the Asian seaweed, Sargassum horneri (Turner) C. Agardh, along the Pacific coast of North America, presents an opportunity to expand our understanding of traits of invasive macroalgae. Here we used surveys to characterize the life history of S. horneri and to quantify traits that promote its spread and persistence, including seasonality in abundance and reproduction, broad habitat affinity, and high reproductive capacity. We found that S. horneri occupies a wide range of suitable depths and substrates, allocates substantial biomass to reproduction, and has seasonal patterns of biomass offset from that of most native macroalgae. A field experiment revealed S. horneri has a high capacity for local dispersal and recruitment that appears sufficient for maintaining populations through multiple generations. Our findings can be paired with knowledge of the life histories of co-occurring species to characterize their potential to interact with S. horneri, which should prove useful for developing best practices for managing its spread.