Seawater carbonate chemistry and processes during experiments with Crassostrea gigas, 2007

This study demonstrated that the increased partial pressure of CO2 (pCO2) in seawater and the attendant acidification that are projected to occur by the year 2300 will severely impact the early development of the oyster Crassostrea gigas. Eggs of the oyster were artificially fertilized and incubated for 48 h in seawater acidified to pH 7.4 by equilibrating it with CO2-enriched air (CO2 group), and the larval morphology and degree of shell mineralization were compared with the control treatment (air-equilibrated seawater). Only 5% of the CO2 group developed into normal 'D-shaped' veliger larvae as compared with 68% in the control group, although no difference was observed between the groups up to the trochophore stage. Thus, during embryogenesis, the calcification process appears to be particularly affected by low pH and/or the low CaCO3 saturation state of high-CO2 seawater. Veliger larvae with fully mineralized shells accounted for 30% of the CO2-group larvae, compared with 72% in the control (p < 0.005). Shell mineralization was completely inhibited in 45% of the CO2-group larvae, but only in 16% of the control (p < 0.05). Normal D-shaped veligers of the control group exhibited increased shell length and height between 24 and 48 h after fertilization, while the few D-shaped veligers of the CO2 group showed no shell growth during the same period. Our results suggest that future ocean acidification will have deleterious impacts on the early development of marine benthic calcifying organisms.

本研究证实，预计至2300年将出现的海水二氧化碳分压（partial pressure of CO2, pCO2）升高及伴随的海水酸化现象，将对长牡蛎（Crassostrea gigas）的早期发育造成严重负面影响。研究人员将该牡蛎的卵进行人工授精后，置于经富二氧化碳空气平衡酸化至pH 7.4的海水中培育48小时（二氧化碳组），并以空气平衡海水为对照组，对比两组的幼虫形态与贝壳矿化程度。尽管在担轮幼虫阶段两组未观察到显著差异，但二氧化碳组仅5%的个体发育为正常的‘D形’面盘幼虫，对照组这一比例则达68%。研究发现，在胚胎发育阶段，高二氧化碳海水的低pH值及/或低碳酸钙饱和态，会对钙化过程造成尤为显著的影响。与对照组72%的占比相比，二氧化碳组中仅30%的幼虫拥有完全矿化的贝壳（p < 0.005）；45%的二氧化碳组幼虫完全未发生贝壳矿化，而对照组这一比例仅为16%（p < 0.05）。对照组的正常D形面盘幼虫在受精后24至48小时内，贝壳长度与高度均有所增加；而二氧化碳组仅存的少量D形面盘幼虫在此期间未出现贝壳生长。本研究结果表明，未来海洋酸化将对海洋底栖钙化生物的早期发育产生有害影响。