Seawater carbonate chemistry and biological processes during experiments with Limacina helicina, 2009@en

Thecosome pteropods (pelagic mollusks) can play a key role in the food web of various marine ecosystems. They are a food source for zooplankton or higher predators such as fishes, whales and birds that is particularly important in high latitude areas. Since they harbor a highly soluble aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The effect of changes in the seawater chemistry was investigated on Limacina helicina, a key species of Arctic pelagic ecosystems. Individuals were kept in the laboratory under controlled pCO2 levels of 280, 380, 550, 760 and 1020 µatm and at control (0°C) and elevated (4°C) temperatures. The respiration rate was unaffected by pCO2 at control temperature, but significantly increased as a function of the pCO2 level at elevated temperature. pCO2 had no effect on the gut clearance rate at either temperature. Precipitation of CaCO3, measured as the incorporation of 45Ca, significantly declined as a function of pCO2 at both temperatures. The decrease in calcium carbonate precipitation was highly correlated to the aragonite saturation state. Even though this study demonstrates that pteropods are able to precipitate calcium carbonate at low aragonite saturation state, the results support the current concern for the future of Arctic pteropods, as the production of their shell appears to be very sensitive to decreased pH. A decline of pteropod populations would likely cause dramatic changes to various pelagic ecosystems.

被壳翼足类（Thecosome pteropods）是一类远洋软体动物（pelagic mollusks），在各类海洋生态系统的食物网中发挥关键作用。它们是浮游动物乃至鱼类、鲸类、鸟类等更高营养级捕食者的食物来源，在高纬度海域尤为重要。由于其壳体为高度可溶性的文石质结构，这类生物对人为二氧化碳排放增加引发的海洋酸化极为敏感。本研究以北极远洋生态系统的关键物种——海若螺（Limacina helicina）为对象，探究了海水化学变化对其的影响。实验个体在实验室中被置于不同梯度的可控二氧化碳分压（pCO2）条件下培养，分压值分别为280、380、550、760及1020 µatm，同时设置了对照温度（0℃）与升温温度（4℃）两个梯度。在对照温度下，海若螺的呼吸速率不受二氧化碳分压的影响；但在升温条件下，呼吸速率随二氧化碳分压升高而显著上升。在两个温度梯度下，二氧化碳分压均对其肠道排空速率无显著影响。以放射性钙-45（45Ca）掺入量表征的碳酸钙（CaCO3）沉积速率，在两个温度梯度下均随二氧化碳分压升高而显著下降，且该下降趋势与文石饱和度状态呈高度相关。尽管本研究证实，被壳翼足类可在较低文石饱和度条件下完成碳酸钙沉积，但研究结果仍支持当前学界对北极被壳翼足类未来生存状况的担忧——其壳体生成过程对海水pH下降极为敏感。被壳翼足类种群数量的下降，可能会引发各类远洋生态系统的剧烈变化。