Archaeologically, the use of marine kelps and seaweeds is poorly understood, yet California's islands are surrounded by extensive and highly productive kelp forests with nearshore habitats containing more than 100 edible species. Historical accounts from around the Pacific Rim demonstrate considerable use of seaweeds and seagrasses by native people, but there has been little discussion of seaweeds as a potential food source on California's islands. This chapter summarizes the biology, diversity, ecology, and productivity of marine macroalgae and marine angiosperms in the California Bight, supporting the likely consumption of seaweeds in the past. The potential use of plentiful and nutritious seaweeds by California Island peoples has major implications for the perceived marginality of the islands.