Results I) Regional Survey

1. Survey Sites Plate Sites Fig. 6: Chiton Effect on Free Space Fig. 5: Chiton Effect on B. violaceus % Free % B. violaceus Figure 3. Temperature Correlations Species Richness Chiton Index Chiton Index % Cover B. violaceus º Celsius Figure 4. % Free Space (grey boxes) and % B. violaceus (color boxes) on Plates During 2006 % Cover Pleasant Harbor Makah Marina John Wayne Marina Lopez IMC Factors Explaining Botrylloides violaceus Success in Washington St. Fouling Communities Erin Grey Department of Ecology & Evolution, University of Chicago, Chicago, IL 60637 Introduction In terrestrial and marine habitats, it is generally accepted that species diversity inhibits invasion success at small scales because diverse communities fully utilize resources1. In terrestrial habitat, at larger spatial scales abiotic factors that favor diversity also favor invasive success, thus leading to an overall positive correlation of diversity and invasive success at the regional level2. Such larger studies are lacking for marine habitats. The purposes of this study were to I) document a large scale pattern of a marine invasion and II) use smaller scale observation and experimental studies to quantify the relative contribution of biotic factors like competition and predation to the success of the invader on settlement plates. II) Spatial Pattern Materials & Methods I) Regional Survey 12 24*24cm random photos were taken underneath docks at 10 marinas with concrete floating docks in early Sept, 2005. Photos were scored for species identity, abundance & free space. Salinity and temperature were also recorded. II) Plate Dynamics 24*24cm acrylic plates were deployed underneath docks at 4 local sites. Plates were censused biweekly from May-Sep 2005-6 for species identity, species abundance, free space and predators. The chiton index was calculated by summing the number of hitons found on a plate during the summer of 2006, then dividing by the number of census dates. • Results I) Regional Survey • Rarefaction curves leveled off across sites, suggesting that the sample effort was sufficient to capture differences between sites (Figure 2). • Mean % cover B. violaceus • negatively correlated with • measures of richness & • diversity (Table 1). • Free space did not correlate • with anything (Table 1). • No significant correlations • in un-averaged data. • (data not shown) • Results II) Plate Dynamics • Competition for Free Space • Mean percent free space and B. violaceus cover on plates at each site • Was calculated for each census date. No statistical analysis has been • performed yet, but it is clear that free space is rarely limiting and that the • abundance of B. violaceus cannot be well-explain by free space. • Chiton Effect Figure 2. Species Richness Rarefaction Curves Sites Figure 1. Map of Study Region # Species Sample # Table 1. Spearman’s ρ for Site Means (*=p<.01, **=p<..001) An analysis of variance was performed to look at the effect of chiton abundance (“chiton index”- see Methods) on both % cover B. violaceus(Fig. 5) and % free space on plates (Fig. 6). Plates were nested within sites, as there were significant differences in chiton abundance among sites. Chitons had no significant effect on B. violaceus abundance but had a significant effect in creating free space on plates (Fig. 6). Washington, USA • Temperature negatively correlated with richness and positively with % cover of B. violaceus (Figure 3). • % B. violaceus: R2= 0.71, p= 0.022 • Species Richness: R2= -0.52, p= 0.125 B. violaceus chiton Plate from John Wayne Marina • Conclusions • At the regional scale of this study, and in contrast to terrestrial studies, no positive correlation between diversity and invasion success was found. • Free space is not correlated with either invasion success or diversity, implying that space-competition is not an important factor. • Temperature appears to explain most of the variation in B. violaceus abundance in the region. • Settlement plates observations also fail to find an obvious relationship between free space and B. violaceus abundance. • Chiton abundance differs significantly among sites and effects the amount of free space, but has no effect on B. violaceus success. • Literature Cited • Stachowicz, J. J., et al. (2002). "Biodiversity, invasion resistance, and marine ecosystem function: Reconciling pattern and process." Ecology83(9): 2575-2590. • Levine, J.M. (2000). “Species diversity and biological invasions: relating local processes to community pattern.” Science288: 761-763 Acknowledgements Special thanks to the Makah Tribe, Pleasant Harbor Marina, John Wayne Marina, Lopez Island Center for allowing me to conduct surveys on their property for 3 years. Research was funded by the EPA-STAR fellowship (FP-91631001) and NSF-DDIG Grant (DEB-0608217)