Search

Foundation species and invasive species strongly influence community diversity and structure, but typically in different ways. However, when widespread invasive species provide novel habitat within a community, their net effect may depend on both the environment and community composition. Fouling communities in northern and southern California harbors were surveyed to determine whether there was variation between two locations in the percent cover of an invasive bryozoan, Watersipora subtorquata (d'Orbigny, 1852), and its relationship to community diversity and composition in these two environments. Diversity significantly differed between locations and had a location-dependent association with W. subtorquata abundance. Communities were significantly dissimilar between locations, and W. subtorquata abundance had the highest percent contribution to community dissimilarity when compared to other species in the community. These results suggest that invasive species may have both facilitative and inhibitive relationships with species in a community, but that the net balance of these interactions depends on both the environmental and community context. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigates the influence of nonnative habitat-forming species on epifaunal fouling communities. It states that several experiments on nonnative species and native species including Watersipora subtorquata, Mytilus galloprovincialis and Ascidia ceratodes were performed in the fouling community in Bodega, California, wherein the associated epifaunal communities of Watersipora subtorquata was compared with other habitat modifiers and structurally similar mimics. Results revealed that the impact of habitat-forming species on epifaunal communities will depend on various factors including the quality of resource the habitat will provide, the epifaunal habitat preferences, and the strength of interactions between epifauna and habitat-forming species.

Both foundation species and introduced species have exceptional influence on community diversity and structure, though they have historically been thought to have opposite effects. However, when introduced species can provide novel habitat within a community, their benefit to the community as a foundation species may outweigh their cost as an invader. The magnitude or direction of species interactions can depend on the environment, thus the net effect of introduced foundation species can vary across different environmental factors. A settlement tile experiment was conducted on the fouling communities of California harbors to determine whether the effects of a widespread invasive bryozoan, Watersipora subtorquata , vary between two locations in its California range, Alamitos Bay and Bodega Harbor. Treatments with live and dead colonies and two sizes of blank tiles were used to evaluate the effects of colony structure and available bare substrate on both mobile and sessile species in the community. Though mobile invertebrate communities in each location across treatments were not significantly dissimilar to each other, communities on large tiles were significantly dissimilar to other communities in each location. Mobile species richness was greatest on live colony and small tiles in Bodega, but greatest on dead colony and large tiles in Alamitos. Both the diversity and community structure of sessile invertebrates across treatments differed significantly between regions. Diversity was greatest on dead colony tiles in Alamitos, where communities were more dissimilar across treatments, but was greatest on live W. subtorquata tiles in Bodega where communities were less dissimilar across treatments. These results highlight the potential for W. subtorquata to have location-dependent net effects on the community throughout its invasive range as a foundation species. • No significant effect of W. subtorquata on benthic community diversity or richness. • Location-dependent effects on benthic community dissimilarity by W. subtorquata. • W. subtorquata competes with colonial tunicates for space; inhibits lateral growth. • Novel example of facilitation; sponge epizoic on W. subtorquata colonies. [ABSTRACT FROM AUTHOR]