Faunal Communities Associated With Sargassum Horneri

Sargassum horneri is a brown macroalga that was introduced to the coast of southern California from Japan in 2003 and has since spread aggressively. S. horneri could have negative ecological and economic impacts on native kelp forest ecosystems by outcompeting native species of algae for limited resources such as space and light. Macroalgae provides important habitat for small invertebrates that form the primary food source for many reef fish. Therefore, changes in the algal community that result from invasive species such as S. horneri could impact higher trophic levels of marine food webs. The meso-invertebrate assemblages associated with S. horneri were studied to characterize the microfaunal prey community using this alga as biogenic habitat and compared to those assemblages on Macrocystis pyrifera, a foundation kelp species native to southern California. S. horneri individuals were collected off the coast of Catalina Island and the invertebrates inhabiting it were preserved, identified, enumerated and measured.  Length-weight relationships were established for the most abundant taxa by measuring and weighing many individuals, and these relationships were used to estimate their biomass. Invertebrate species abundance and biomass were compared to assemblages on M. pyrifera, using data from a previous study done at Catalina Island. The meso-invertebrate community associated with the two species of algae varied substantially, suggesting that the displacement of M. pyrifera by S. horneri has the potential to alter the species composition and abundance of prey available to reef fishes and lead to a restructuring of the food web in southern California kelp forests.