Ocean acidification, the ongoing reduction of surface ocean seawater pH and free CO32- due to absorption of surplus atmospheric CO2, is a symptom of global change that poses challenges to marine life. While much research investigates ocean acidification impacts on external calcifiers, less considers its impacts on internal calcifiers, whose calcification is relatively isolated from seawater chemistry. Among these are teleost fishes, which calcify otoliths within their inner ear capsules. Counter to hypotheses that otoliths will remain immune to acidifying seawater, it is now understood that they are indirectly impacted: HCO3- retained in the bloodstream to buffer acidosis moves into the endolymph where it serves as substrate for CaCO3 precipitation, contributing to abnormal otolith growth. While several studies have demonstrated that ocean acidification enhances otolith growth and alters otolith shape, further questions remain unanswered. This dissertation includes three research projects that expand on the existing literature: Chapter I provides the most thorough review of ocean acidification impacts on otoliths available; Chapter II (Holmberg et al. 2019a) is the first study to investigate and demonstrate ocean acidification impacts on all three otolith types, and uses scanning electron microscopy to investigate novel otolith morphological metrics in Clark’s anemonefish, Amphiprion clarkii; Chapter III (Holmberg et al. 2019b) repeats this methodology and corroborates the outcome, albeit with the smallmouth grunt (Haemulon chrysargyreum), a species boasting a three times-longer larval phase for maximum exposure time; Chapter IV (Holmberg et al. 2019c) is one of only three studies that used chemometrics to investigate ocean acidification impacts on CaCO3 polymorph
replacement in fish otoliths, and used attenuated total reflectance Fourier-transform infrared spectroscopy to analyze H. chrysargyreum sagittae. Thus far, several effects of elevated pCO2 were observed in these species, including enhanced otolith size, lateral development, and surface roughness, as well as altered otolith shape. These impacts may impair sensory perception in teleost fishes, with implications for fitness. All experiments contribute to a growing knowledge base serving to aid predictions of teleost fitness in the future ocean.
Holmberg R. J., 2019. Ocean acidification impacts on teleostean otolith development. PhD thesis, University of Massachusetts Boston. Thesis (restricted access).