Effects of ocean acidification caused by rising CO2 on the early development of three mollusks

Increasing atmospheric CO2 can decrease seawater pH and carbonate ions, which may adversely affect the larval survival of calcareous animals. In this study, we simulated future atmospheric CO2 concentrations (800, 1500, 2000 and 3000 ppm) and examined the effects of ocean acidification on the early development of 3 mollusks (the abalones Haliotis diversicolor and H. discus hannai and the oyster Crassostrea angulata). We showed that fertilization rate, hatching rate, larval shell length, trochophore development, veliger survival and metamorphosis all decreased significantly at different pCO2 levels (except oyster hatching). H. discus hannai were more tolerant of high CO2 compared to H. diversicolor. At 2000 ppm CO2, 79.2% of H. discus hannai veliger larvae developed normally, but only 13.3% of H. diversicolor veliger larvae. Tolerance of C. angulata to ocean acidification was greater than the 2 abalone species; 50.5% of its D-larvae developed normally at 3000 ppm CO2. This apparent resistance of C. angulata to ocean acidification may be attributed to their adaptability to estuarine environments. Mechanisms underlying the resistance to ocean acidification of both abalones requires further investigation. Our results suggest that ocean acidification may decrease the yield of these 3 economically important shellfish if increasing CO2 is a future trend.

大气二氧化碳浓度升高可降低海水pH值与碳酸盐离子浓度，进而可能对钙化动物的幼体存活产生不利影响。本研究模拟了未来大气二氧化碳浓度梯度（800、1500、2000及3000 ppm），探究了海洋酸化对3种软体动物——杂色鲍（Haliotis diversicolor）、皱纹盘鲍（Haliotis discus hannai）以及葡萄牙牡蛎（Crassostrea angulata）早期发育的影响。研究结果显示，在不同pCO₂水平下，受试生物的受精率、孵化率、幼体壳长、担轮幼虫发育状态、面盘幼虫存活率及变态率均显著下降（牡蛎孵化率除外）。相较于杂色鲍，皱纹盘鲍对高CO₂环境的耐受性更强：当CO₂浓度为2000 ppm时，皱纹盘鲍面盘幼虫的正常发育率可达79.2%，而杂色鲍面盘幼虫的正常发育率仅为13.3%。葡萄牙牡蛎对海洋酸化的耐受性则优于两种鲍类；在3000 ppm CO₂浓度下，其D形幼虫的正常发育率仍可达50.5%。葡萄牙牡蛎对海洋酸化的这种显著抗性，可能与其对河口生境的适应性有关。两种鲍类抵御海洋酸化的内在机制仍有待进一步研究。本研究结果表明，若未来大气CO₂浓度持续升高，海洋酸化可能会降低这3种具有重要经济价值的贝类的产量。