| The ability of humans to transport species across geographic boundaries has created a substantial threat to many habitats via the introduction of non-native species. These invaders have the potential to alter many aspects of the communities that they invade. Zostera japonica Aschers. & Graebn. is an intertidal angiosperm that was introduced to Washington State from Japan. This abundant species has spread and continues to colonize new mudflat habitat throughout Washington, Oregon, B.C. Canada, and most recently, California. Understanding the impacts of this invader is essential both from a scientific and a management perspective.; This research examined impacts of the invasive seagrass Z. japonica , in Padilla Bay, Washington. By using a series of transplants I was able to show that Z. japonica has substantial impacts at the population, community, and ecosystem level. At the population level, beds of eelgrass transplanted to different tidal zones showed that the growth potential of Z. japonica is not limited by tidal zone at sites that retain water during low tide. In addition, competition was found between the invader and the native eelgrass, Zostera marina L., with each species having a negative effect on shoot density in the other. In addition, leaves of the native species were shorter when grown with the invader.; At the community level, the benthic and infaunal assemblages associated with the invader differed form plots in which the vegetation had been removed. However, assemblages associated with Z. japonica did not significantly differ from the assemblages associated with the native eelgrass. Tidal zone and site were also very important in determining the assemblage of organisms.; At the ecosystem level, I found that Z. japonica changed the microbial community in the sediment compared to the native species. Z. japonica also decomposed faster than the native eelgrass. Though the impacts of this invader were highly variable across sites within the bay, the combination of these results strongly suggests that Z. japonica will have large impacts on community and ecosystem processes as it continues to spread along the west coast of North America. |
