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CRAMP Rapid Assessment. Reference Site Analysis
Reference sites were selected by the level of perceived impact. Sites selection was based on inaccessibility, access, and level of protection. This was assessed qualitatively to avoid a circular argument where the quantified data is used both to select and analyze the sites. This provides an external means of defining the reference conditions used to compare against impacted areas.
Transformed and original values were evaluated to determine the degree of variability. Measurements of the coefficient of variation (CV) were used to determine which transformations were most appropriate for each factor (=stdev(X)/mean(X)*100). Stronger transformations were applied to reduce concerns of leverage. Factors that would be considered to have large effects on the results included: coral species, silt, mud, sand, calcareous algae, macroalgae, small fish, introduced fishes, planktivores, sessile invertebrate trophic level, and age of islands even after transformations. These parameters all had CV’s that exceeded 100.
A cluster analysis was then conducted to compare the selected reference sites to see if they fell into distinct groups in a dendrogram. The cluster analysis was not used for any strict inference, hypothesis testing, or development of sites, only to see how similar the selected reference sites are to the whole suite of sites. A similarity matrix was constructed within PRIMER analyzing between sites, using a Bray-Curtis similarity measure. Since initial reference site selection was based on depth and exposure, all wave and depth parameters were excluded. Twenty-nine biotic and abiotic parameters were used.
A cluster analysis using only the reference sites showed that there was considerable overlap and that habitat types were not all closely related to each other.
Dendrogram depicting similarity of reference sites to determine if habitat types can be discriminated.
Boxplots and descriptive analyses of each variable by the six habitat types revealed which factors were most important in explaining the differences in habitat type.
Boxplot of total coral cover by habitat type using reference sites. 1=sheltered <5m, 2=Exposed < 5m, 3=Sheltered 5-10m, 4=Exposed 5-10m, 5=Sheltered >10m, 6=Exposed >10m.
Habitat differences for each factor were then confirmed using formal tests. One-way ANOVA’s showed the following factors to be significantly different by habitat type: total coral cover, sand, substrate, population within10km, and age.
It was then necessary to determine if the reference sites were environmentally different from the non-reference sites. A Principal Components Analysis (PCA) was used to evaluate how well the sites were separated.
Principal components analysis of environmental variables of reference and non-reference sites (n=172)
Next, it was necessary to determine if the reference sites in a given habitat class were different from the reference sites in other classes and how much each factor contributed to the differences.
Principal components analysis of reference sites by habitat class. 1=sheltered <5m, 2=Exposed < 5m, 3=Sheltered 5-10m, 4=Exposed 5-10m, 5=Sheltered >10m, 6=Exposed >10m.
Habitat differences for each factor were then confirmed using formal tests.
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A discriminant analysis was performed to determine if the reference sites fell within their predicted habitat class.
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An analysis of variance (ANOVA) was used to determine which variables influenced these reference site similarities and which factors were significantly different between habitat classes.
One-way ANOVA’s showed the following factors to be significantly different by habitat type: total coral cover, sand, substrate, human population within10 km, and age of the site.
Last Update: 04/21/2008
By: Lea Hollingsworth
Hawai‘i Coral Reef Assessment & Monitoring Program
Hawai‘i Institute of Marine Biology
P.O. Box 1346
Kāne‘ohe, HI 96744
808-236-7440 phone
808-236-7443 fax
email: jokiel@hawaii.edu