Early larval development of the Sydney rock oyster Saccostrea glomerata under near-future predictions of CO2 driven ocean acidification

Anthropogenic emissions of carbon dioxide (C02) from fossil fuel combustion and deforestation are rapidly increasing the atmospheric concentration of CO2 and reducing the pH of the oceans. This study shows that predicted near-future levels of ocean acidification have significant negative effects on early larval development of the Sydney rock oyster Saccostrea glomerata (Gould, 1850). CO2 was added to seawater to produce pH levels set at 8.1 (control), 7.8, and 7.6 (actual pH values were 8.11,7.81, and 7.64, respectively). These treatments represent present-day surface ocean pH, as well as upper (.6. pH ~ -0.3) and lower (.6. pH ~ -0.5) pH predictions for the surface oceans in 21 00. With decreasing pH, survival of S. glomerata larvae decreased, and growth and development were retarded. Larval survival decreased by 43% at pH 7.8 and by 72% at pH 7.6. Antero-posterior measurement (APM) was reduced by 6.3% atpH 7.8 and 8.7% atpH 7.6, and dorso-ventral measurement (DVM) was reduced by 5.1 % at pH 7.8 and 7.5% at pH 7.6. The percentage of empty shells remaining from dead larvae decreased by 16% at pH 7.8 and by 90% at pH 7.6 indicating that the majority of empty shells dissolved within 7 days at pH 7.6. Scanning electron microscope images of 8-day-old larvae show abnormalities on the shell surface at low pH suggesting (1) problems with shell deposition, (2) retarded periostracum formation, and/or (3) increased shell dissolution. Larval life-history stages are considered particularly susceptible to climate change, and this study shows that S. glomerata larvae are sensitive to a high-C02 world and are, specifically, negatively affected by exposure to pH conditions predicted for the world's oceans for the year 2100