Figure 1. Schematic representation of the relationship between fertilization success and sperm concentration of Heliocidaris erythrogramma at different pH levels, assuming a negative pH impact on fertilization.

Determining fertilization success at an intermediate sperm concentration (here, the sperm concentration that generates 50% of maximum observed fertilization success in controls) yields maximum sensitivity in the assay. All data in Fig. 1Figure 1 are theoretical. FSR_{max Control} = maximum fertilization success in Controls; FSR_{50 Control} = 50% of maximum fertilization success in Controls; F _{max Control} = sperm concentration that generates maximum fertilization success in Controls; F _{50 Control} = sperm concentration that generates 50% of maximum fertilization success in Controls. FSR_{50 pH 7.8} = observed fertilization success in pH 7.8 treatment at the sperm concentration that generates 50% of maximum fertilization success in Controls; FSR_{50 pH 7.6} = observed fertilization success in pH 7.6 at the sperm concentration that generates 50% of maximum fertilization success in Controls. Actual fertilization curves vary for each individual pair.