Community Changes Associated with the Spread of an Introduced Seagrass, Zostera Japonica

Species introductions have provided a valuable source of information for understanding the factors that regulate community composition. However, the effect of such introductions has often been obscured by a lack of information on distribution and abundance patterns before or during an invasion event. I examined the changes in a benthic community associated with the ongoing spread of an introduced seagrass, Zostera japonica, by sampling transplanted seagrass plots and established Z. japonica patches of known ages. The sedimentary and faunal changes associated with Z. japonica were similar to those observed with native seagrass species. Mean sediment grain size declined and sediment volatile organics increased within Z. japonica patches. Faunal richness was higher within Z. japonica patches compared with adjacent unvegetated areas, and many numerically dominant species were positively associated with this introduced seagrass. However, the effects of Z. japonica on faunal abundance varied with both the age of a seagrass patch and site location. The introduction of this seagrass has thus changed the physical habitat as well as the richness and densities of resident fauna. Many studies of introduced species have concentrated on direct interactions between introduced and native organisms. In contrast, the community changes associated with the introduction of Z. japonica emphasize the potential importance of indirect and system—level effects of introduced species on community composition.