Ocean Acidification and Fertilization in the Antarctic Sea Urchin Sterechinus neumayeri: the Importance of Polyspermy

Ocean acidification (OA), the reduction of the seawater pH as a result of increasing levels of atmospheric CO₂, is an important climate change stressor in the Southern Ocean and Antarctic. We examined the impact of OA on fertilization success in the Antarctic sea urchin Sterechinus neumayeri using pH treatment conditions reflective of the current and near-future “pH seascape” for this species: current (control: pH 8.052, 384.1 μatm of p_CO2), a high CO₂ treatment approximating the 0.2–0.3 unit decrease in pH predicted for 2100 (high CO₂: pH 7.830, 666.0 μatm of p_CO2), and an intermediate medium CO₂ (pH 7.967, 473.4 μatm of p_CO2). Using a fertilization kinetics approach and mixed-effect models, we observed significant variation in the OA response between individual male/female pairs (N = 7) and a significant population-level increase (70–100%) in t_b (time for a complete block to polyspermy) at medium and high CO₂, a mechanism that potentially explains the higher levels of abnormal development seen in OA conditions. However, two pairs showed higher fertilization success with CO₂ treatment and a nonsignificant effect. Future studies should focus on the mechanisms and levels of interindividual variability in OA response, so that we can consider the potential for selection and adaptation of organisms to a future ocean.