Effects of Sargassum muticum on native
marine communities

Karen Osborn
Monterey Bay Aquarium Research Institute

Wednesday, August 25, 1999
3:00 p.m.—Pacific Forum

The epibiont community associated with Sargassum muticum in northern Puget Sound (San Juan Islands) was examined from May to September 1997. Abundance and species richness of epibiont communities were determined as well as the relationships between faunal abundance and plant size, particulate load, and polyphenolic concentration of S. muticum. One hundred and seven epifaunal taxa were identified from S. muticum. Faunal communities on S. muticum were compared with those on Laminaria saccharina, a native alga displaced by S. muticum.

S. muticum is able to support a more abundant and species rich community than the native alga L. saccharina (mean of 20 species/plant compared to 10 species/plant on L. saccharina) because of its high degree of morphological complexity. Only two species never occurred on S. muticum that were common on L. saccharina, whereas 15 species were common on S. muticum but never found on L. saccharina. Abundance of fauna increased as S. muticum biomass increased through time. No relationship was found between polyphenolic concentration (1 – 2% dry weight) and herbivore abundance. The particulate load on S. muticum was heavy and consisted primarily of diatoms.

Epibiont diversity and abundance increase in areas invaded by S. muticum because of the increased habitat, productivity, and complexity that S. muticum provides. For this reason, elimination of S. muticum is not recommended based on the impact S. muticum has on epifauna. However, S. muticum may negatively affect water movement, light penetration, sediment accumulation, and anoxia at night. Further research is needed before management decisions can be made regarding S. muticum.

Next: 1999 Annual Intern Symposium