UCLA

Southern California is home to native macroalgae in the Sargassaceae family (order Fucales); several function as canopy-forming species in lower intertidal and subtidal ecosystems and act as foundational species by providing food and habitat for an array of organisms. The two genera found in this family are Stephanocystis and Sargassum. Among these, two endemics are the focus of my studies, Stephanocystis dioica and Sargassum agardhianum, which are warm-temperate species whose natural range begins south of Point Conception. As ocean temperatures continue to warm in Southern California, such warm-temperate canopy-forming species may play an increasingly important ecological role as community structure shifts. Despite this, foundational knowledge, including their reproductive biology, remains poorly understood.For S. dioica, I documented the reproductive phenology, identified the morphology of both sexes, and performed a series of experiments to culture embryos and juveniles. A novel ex-situ culture protocol successfully supported embryo and juvenile survival for up to 12 weeks. The reproductive phenology of S. agardhianum was documented establishing a summer-fall reproductive window. A morphological and histological study confirmed a monoecious habit and provided clear visualization of reproductive structures. These data provide a foundational tool for future research into the early life history and restoration potential of these native species. For S. agardhianum, herbarium records, iNaturalist observations, and field surveys were used to investigate its past and present distribution in Los Angeles and Orange Counties. Populations in Orange County appear stable, potentially reflecting lower urbanization, reduced ocean discharge volumes, and lower human foot traffic. In contrast, in the Palos Verdes Peninsula (PVP; LA County) my surveys detected S. agardhianum at fewer locations than historically recorded, hypothesized to reflect anthropogenic stressors including decades of sewage discharge and human foot traffic. The northern edge of the range was found to be one site in PVP, shifted from historical Malibu. In contrast, populations in Orange County appear stable, potentially reflecting lower urbanization, reduced ocean discharge volumes, and lower human foot traffic. , making this site a key location for future work as our ocean warms. Together, these studies provide foundational tools and baseline data for future research into the reproductive ecology, distribution, and conservation of these understudied warm-temperate native Sargassaceae.