Reprint Series No. 30
Reprinted March 2000

EFFECTS OF THE INVASIVE SEAWEED SARGASSUM MUTICUM ON NATIVE MARINE COMMUNITIES IN NORTHERN PUGET SOUND, WASHINGTON

Karen J. Giver

 

May 1999

Bibliographic Citation
Giver, Karen J. 1999. Effects of the invasive seaweed Sargassum muticum on native marine communities in northern Puget Sound, Washington. Master of Science Thesis, Western Washington University, Bellingham, Washington. 93 pp. Washington State Department of Ecology (Publication No. 00-06-010), Padilla Bay National Estuarine Research Reserve Reprint Series No. 30.

Abstract
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 on 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 L. saccharina (mean of 20 species/plant compared to 10 species/plant on L. saccharina ) because of it's 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. S. muticum may affect water movement, light penetration, sediment accumulation and anozia at night. Further research is needed before management decisions can be made regarding S. muticum.