Invasion
Invasion Description
1st Record: San Juan Islands/WA/Rocky and Andrews Bays, Straits of Juan de Fuca (1948, Scagel 1956)
Geographic Extent
San Juan Islands/WA/Rocky and Andrews Bays, Straits of Juan de Fuca (1948, Scagel 1956); San Juan Islands/WA/Jackle and Argyle Lagoons (19, Straits of Juan de Fuca (1956, Scagel 1956); Cypress, Guemes, and Hat Islands, San Juan Islands/WA/Straits of Juan de Fuca (Giver 1999)
Vectors
| Level | Vector |
|---|---|
| Probable | Oyster Accidental |
Regional Impacts
| Ecological Impact | Competition | |
| The invasion of Sargassum muticum resulted in displacement of native algae, in the San Juan Islands, northern Puget Sound. A removal experiment resulted in recovery of native kelps (Britton-Simmons 2004). Modeling and experiments indicated that S. muticum invasions required a combination of disturbance and high propagule pressure (Britton-Simmons et al. 2008). | ||
| Ecological Impact | Food/Prey | |
| Sargassum muticum was grazed by a high abundance, but low diversity of grazers, compared to native seaweeds. Common grazers were the amphipods Peramphithoe mea, Aoroides columbiae, Caprella laeviscula and Ischyocerus anguipes, and the snail Lacuna variegata. Much of the grazing was on periphytic diatoms, and the tissue consumption mostly occurs during the period of slow growth, before the annual dieback, and does not affect the seasonal abundance or dominance of the plant (Norton and Benson 1983). There were fewer Green Sea Urchins (Strongylocentrotus droebachiensis) at invaded sites, apparently because they found S. muticum unpalatable (Britton-Simmons 2004). However, the snail Lacuna vincta was 2-9X more abundant on S. muticum than on native algae. This preference seems to have been acquired in the last 30 years (Britton-Simon et al. 2011). | ||
| Ecological Impact | Habitat Change | |
| In the San Juan Islands, Washington, Sargassum muticum supported a total of 107 epifaunal taxa, and on average supported 20 species per plant, compared to 10 species per plant on the native kelp Laminaria saccharina. Epifaunal diversity increased in area invaded by S. muticum (Giver 1999). | ||