Zebra mussel density on rocks (white boxplots) and on hydrilla (grey boxplots) and mean by treatment for Hydrilla vs Rock as substrates in June 2022 for sites where rocky substrates were dominant. 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. Asterisks above the diagram denote statistically significant differences between attachment surfaces (rocks vs. hydrilla) at each site (paired student’s t-test, * p-value < 0.05, ** p-value < 0.01, *** p-value < 0.001).