Hydrilla biomass (a, c) and zebra mussel density on hydrilla (b, d) at different sites (a, b) and mean by treatment at muddy vs. rocky sites (c, d). The lower and upper lines of the boxplots represent the 25th and 75th percentiles and the bold line represents the median. Data falling outside the percentile range are plotted as outliers. Different letters denote significant differences (Tukey HSD pairwise comparison, p-values < 0.05). Differences between muddy vs. rocky sites (c, d) were not significant.