| Concerns over the ecological and economic harms associated with non-native seaweeds have generated much interest in the factors influencing the invasion process. Despite the increasing presence of non-native seaweeds in coastal habitats, little is known about the response of herbivores to these algal invaders. I conducted experimental studies to determine the edibility of non-native seaweeds by comparing the feeding rates of native macroalgal consumers in single-food trials on non-native and native seaweeds. Macroalgae-eating native consumers included the sea hare Aplysia californica, the snail Chlorostoma aureotincta, the crab Pachygrapsus crassipes, and the urchin Strongylocentrotus purpuratus. I selected non-native seaweeds with different periods of residency in southern California waters, including species with a >25-year history of population establishment (Sargassum muticum), and those that have appeared in the last five years (Caulacanthus ustulatus, Sargassum filicinum, and Undaria pinnatifida). The urchin grazer, S. purpuratus, was the only species to consume native seaweeds more rapidly than non-native seaweeds. In contrast, the gastropods A. californica and C. aureotincta selectively fed on non-native seaweeds faster than native seaweeds. The crab P. crassipes showed no preferences. Among seaweed invaders, U. pinnatifida was the most palatable food whereas S. muticum was consistently eaten at the slowest rates. For the edible U. pinnatifida , herbivore control will likely depend on the intensity of grazing pressure in the field. The Sargassum congeners and C. ustulatus will likely experience less herbivore regulation due to their structural and chemical attributes. |
