Sea urchin fertilization in a warm, acidified high pCO2 ocean across a range of sperm densities

Marine invertebrate gametes are being spawned into an ocean simultaneously warming, acidifying and increasing in pCO₂. Decreased pH/increased pCO₂ narcotizes sperm indicating that acidification may impair fertilization, exacerbating problems of sperm limitation, with dire implications for marine life. In contrast, increased temperature may have a stimulatory effect, enhancing fertilization. We investigated effects of ocean change on sea urchin fertilization across a range of sperm densities. We address two predictions: (1) low pH/increased pCO₂ reduces fertilization at low sperm density and (2) increased temperature enhances fertilization, buffering negative effects of acidification and increased pCO₂. Neither prediction was supported. Fertilization was only affected by sperm density. Increased acidification and pCO₂ did not reduce fertilization even at low sperm density and increased temperature did not enhance fertilization. It is important to identify where vulnerabilities lie across life histories and our results indicate that sea urchin fertilization is robust to climate change stressors. However, developmental stages may be vulnerable to ocean change.