Spread and impact of the introduced Japanese seaweed, (Sargassum muticum) in native kelp forests of the San Juan Archipelago (yr. 2)

J. Timothy Wootton, The University of Chicago
$31,595

The introduction of species into habitats outside their normal geographic range is accelerating as human mobility increases. Introduced species have the potential to radically alter the structure and function of native ecosystems and are a leading threat to biodiversity. The Japanese alga Sargassum muticum has been invading kelp forests in the San Juan Islands of Washington since its introduction nearly fifty years ago (Scagel 1956). Despite its widespread distribution as an exotic in North America and Europe very little is known about how S. muticum impacts native communities. Subtidal kelp communities in the San Juan Islands are important habitat for a wide variety of animals including invertebrates, fish, mammals and birds. Furthermore, the kelp species that dominate these plant assemblages add three-dimensional structure to the habitat and are important sources of carbon in coastal food webs. Therefore, any widespread effects of S. muticum on these algal communities are likely to have broader consequences for the nearshore ecosystem in this region. We are using an experimental approach to explore the dynamics and consequences of the S. muticum invasion in the San Juan Islands.

In 2002, our research will focus on three projects: I) continued monitoring of S. muticum removal experiments in order to compare long and short term responses of the native community to S. muticum removal, 2) testing a possible indirect interaction pathway involving S. muticum, native kelp species and their shared herbivore, the native snail Lacuna vincta, and 3) exploring the phenomenon of biotic resistance by experimentally evaluating the role of native functional groups in resisting invasion by S. muticom. Our results will provide additional insight into the impacts of this ongoing invasion on the native plant and animal biota of the San Juan Islands. In particular, our work in 2002 may contribute valuable information about long versus short term dynamics and the role of indirect effects in the invasion process. Furthermore, our research on the role of native functional groups in resisting invasion will enhance our (presently limited) understanding of the phenomenon of biotic resistance. By increasing our understanding of the dynamics and consequences of this invasion, we may also gain insight into possible mitigation strategies. This study will provide critical information regarding how important a threat S. muticum is to the integrity of the coastal ecosystem in this region.