Ocean acidification may have deleterious effects on many species, but anticipating long-term changes in the abundance of populations will require an understanding of ocean acidification as an evolutionary force. Here, I show that ocean acidification alters natural selection on offspring size and is likely to drive contemporary evolution. In a detailed study of a coastal fish species (California grunion), I demonstrate that larval mortality is highly sensitive to ocean acidification and that mortality rates are lower for larger larvae. However, these effects are countered by tradeoffs between offspring size and number, suggesting that measurements of maternal fitness are critical for quantifying selection through ocean acidification. Measurements of selection and genetic variation were used to project the evolution of larval size as seawater conditions changed incrementally over many decades. Results for California grunion suggest that contemporary evolution may offset the projected decline in reproductive success by about 50%.

海洋酸化可能对许多物种产生有害影响，但要预测种群数量的长期变化，需要了解海洋酸化是一种进化力量。在这里，我表明海洋酸化改变了对后代大小的自然选择，并可能推动当代进化。在对沿海鱼类（California grunion）的详细研究中，我证明了幼虫死亡率对海洋酸化高度敏感，并且较大的幼虫死亡率较低。然而，这些影响被后代大小和数量之间的权衡所抵消，这表明母体健康的测量对于通过海洋酸化量化选择至关重要。随着海水条件在几十年内逐渐变化，选择和遗传变异的测量被用来预测幼虫大小的演变。加利福尼亚 grunion 的结果表明，当代进化可能抵消预计的繁殖成功率下降约 50%。