Two-way ANOVA for percent motility (A) and sperm speed (B) of <i>Heliocidaris erythrogramma</i> across different pH treatments (fixed) and males (random).

<p>Significant effects (<i>P</i>≤0.05) are shown in bold.</p

Scatterplots for observed (FSR_obs) versus modelled (FSR_mod) fertilization success for pH 7.8 (A) and 7.6 (B).

<p>Regression analyses revealed a significant relationship between observed (independent) and modelled fertilization (dependent) for pH 7.8 (<i>P</i> = 0.012, r² = 0.336), but not for pH 7.6 (<i>P</i> = 0.413, r² = 0.042).</p

Seawater parameters for the three different pH treatments.

<p>pH<b>_NBS</b>, temperature (T), salinity (Sal) and total alkalinity (A_T) were measured directly and used to compute partial pressure levels of carbon dioxide (<i>p</i>CO₂) and seawater saturation states for calcite and aragonite (Ω_Ca and Ω_Ar respectively) using CO2SYS. Means ± S.E.</p

Modelled (FSR_mod) and observed (FSR_obs) fertilization success for each urchin pair under acidified conditions (pH 7.6 and 7.8), and parameters from Control observations (pH 8.1) used in modelling FSR_mod at lowered pH levels.

<p>FSR_{50 Control} = 50% of maximum fertilization success in Controls; <i>F</i>_{50 Control} = sperm concentration that generates 50% of maximum fertilization success in Controls. Sperm data from each male in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053118#pone-0053118-t002" target="_blank">Table 2</a> were used in modelling FSR_mod. No females were spawned for male A.</p

Ocean acidification effects on sperm speed and percent sperm motility for each male <i>Heliocidaris erythogramma</i>.

<p>Significant differences in parameters between sites (<i>P</i>≤0.05) are shown in bold.</p

Impacts of ocean acidification on sperm motility and sperm swimming speed in <i>Heliocidaris erythrogramma.</i>

<p>Proportion of mean (±S.E.) motile sperm (A) and sperm speed (B) at different levels of ocean acidification (pH mediated by CO₂ addition). Lower case letters indicate significantly different groups at <i>p</i> = 0.05 (Tukey’s test). (C) Mean logarithmic response ratios (±95% CI) of effects of ocean acidification on percent motility and sperm speed (n = 19).</p

Two-way ANOVA for observed (FSR_obs; A) and modelled fertilization success (FSR_mod; B) of <i>Heliocidaris erythrogramma</i> across different pH treatments (fixed) and males (random).

<p>Significant effects (P≤0.05) are shown in bold.</p

Effects of ocean acidification on fertilization success (FSR) in <i>H. erythrogramma</i>.

<p>(A) Mean (±S.E.) observed (FSR_obs) and modelled fertilization success (FSR_mod) for pHs 7.6 and 7.8, and mean (±S.E.) FSR₅₀ (50% of maximum FSR) for pH 8.1. (B) Bootstrapped mean logarithmic response ratios (±95% CI) of effects of ocean acidification on FSR_obs and FSR_mod. FSR_mod shows change in fertilization success expected due to ocean acidification’s influence on sperm swimming behaviour (Fig. 2C). (n = 18 replicate trials). See text for details.</p