The early life stages of an estuarine fish, the red drum (Sciaenops ocellatus), are tolerant to high pCO2

Ocean acidification (OA) and other climate change induced environmental alterations are resulting in unprecedented rates of environmental deterioration. This environmental change is generally thought to be too fast for adaptation using typical evolutionary processes, and thus sensitivity may be dependent on the presence of existing tolerant genotypes and species. Estuaries undergo natural pCO(2) fluctuations over a variety of time scales, and levels regularly exceed the predicted end of the century values. Interestingly, estuarine fish species have been overlooked in reference to the impacts of OA. Here, we use the estuarine red drum (Sciaenops ocellatus) as a model to explore the hypothesis that early life stages of estuarine species have intrinsic tolerance to elevated pCO(2). Our sensitivity endpoints included: survival, growth, yolk consumption, heart rate, and scototaxis. Survival was significantly decreased when exposed to 1300 latm and 3000 latm, and coincided with a significant increase in heart rate at the 3000 latm exposure. However, these effects were less pronounced than the findings of previous studies on other marine fish species. Yolk depletion rate and standard length were not significantly affected by pCO(2). Scototaxis behaviour was also not significantly affected by exposure to elevated levels of pCO(2) under both acute and acclimated exposure scenarios. Overall, these results support the hypothesis that estuarine life history and habitat usage may play a critical role in determining sensitivity of fish species to OA. Furthermore, estuarine species may provide present-day insight into the physiological and ecological foundation of OA tolerance.