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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.
Results I) Regional Survey
Results II) Plate Dynamics
Rarefaction curves leveled off across sites, suggesting that the sample effort
was sufficient to capture differences between sites (Figure 2).
Figure 2. Species Richness Rarefaction Curves
Sites
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.
Figure 4. % Free Space (grey boxes) and % B. violaceus (color boxes) on Plates During 2006
Figure 1. Map of Study Region
# Species
% Cover
Survey Sites
Plate Sites
Makah Marina
Sample #
II) Plate Dynamics
B. violaceus
chiton
Plate from John Wayne Marina
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.
Figure 3. Temperature Correlations
35
•Temperature negatively correlated
with richness and positively with %
cover of B. violaceus (Figure 3).
30
25
20
Fig. 6: Chiton Effect on Free Space
%
Free
15
% B. violaceus:
Species Richness:
10
5
R2= 0.71, p= 0.022
R2= -0.52, p= 0.125
Chiton Index
0
11
12
13
14
15
16
17
º Celsius
Conclusions
1.
2.
3.
4.
5.
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
Acknowledgements
1.
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)
2.
Pleasant
Harbor
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).
Fig. 5: Chiton Effect on B. violaceus
(data not shown)
Lopez IMC
Chiton Effect
% B. violaceus
Washington, USA
•Mean % cover B. violaceus Table 1. Spearman’s ρ for Site Means (*=p<.01, **=p<..001)
negatively correlated with
%B
S
Alpha
Free
measures of richness &
diversity (Table 1).
-0.88**
-0.85*
-0.16
%B
•Free space did not correlate
0.95**
0.17
with anything (Table 1).
S
•No significant correlations
.0.01
Alpha
in un-averaged data.
John Wayne
Marina
Stachowicz, J. J., et al. (2002). "Biodiversity, invasion resistance, and marine ecosystem function: Reconciling pattern and process." Ecology 83(9): 25752590.
Levine, J.M. (2000). “Species diversity and biological invasions: relating local processes to community pattern.” Science 288: 761-763
Chiton Index