2.7. Data analyses
Due to difficulty distinguishing sea bream (Archosargus rhomboidalis) and pinfish (Lagodon rhomboides) in the field, survey data for these two species were grouped for analysis. Variation in square-root-transformed herbivore abundance was evaluated using a two-way analysis of
variance (ANOVA) on square root transformed herbivore abundance data, with site and sampling time as fixed factors. Post-hoc tests on the species factor were conducted using Sidak's pairwise comparisons. Data from herbivory assays (% biomass loss per PU) were not normally distributed (Shapiro–Wilk test, p b 0.05), and were ranktransformed prior to analysis. The potential for a caging artifact was analysed using using a one-way ANOVA with herbivore exclusion treatment as a fixed factor, followed by Sidak's post hoc comparisons. Differences in biomass loss between the uncaged and partial cage treatment was used as the indicator of caging artifact. Variation in herbivory pressure was analysed using a three-way ANOVA on rank-transformed biomass loss data, with seagrass species, site, and time as fixed factors. Sidak's post hoc pairwise comparisons were used for significant main effects, and on the site × time ×
species interaction, to evaluate herbivory pressure across seagrass species at different times of the year at each site. Variation in C:N and C:P ratios of seagrasses from Pelican Shoal
(the donor site) was evaluated using two-way ANOVA (with species and time as factors) and Sidak's post-hoc comparisons on ranktransformed C:N ratios and on untransformed C:P ratios, with species and sampling time as fixed factors. Donor seagrasses from Pelican Shoal and ambient seagrasses from each assay sites were compared for potential differences in elemental composition. Pairwise comparisons were conducted on seagrass C:N and C:P ratios between the donor site and assay site for each site/ species/time combination. For elemental variables with normal distributions (C:P — all species; C:N — T. testudinum and H. wrightii), independent sample t-tests were used. Mann–Whitney U-tests were used for data with non-normal distributions (C:N — S. filiforme). C:N and C:P ratios, temperature, salinity, and herbivorous fish abundance were used in stepwise multiple regression analyses to predict seagrass biomass loss. In each of the two regression analyses conducted, herbivory assay data from the three uncaged and partial
cage treatments were pooled, and data from each seagrass species at each site were treated as a replicates (n = 12 replicates per sampling event). The first analysis included C:N and C:P ratios, temperature, and salinity for all four sampling events (n = 48). The second analysis included herbivorous fish abundance in addition to C:N ratios, C:P ratios, temperature, and salinity. However, because fish surveys were conducted on only two of the four sampling events, the second analysis only included data from the Fall and Winter sampling events (n = 24).