Seawater carbonate chemistry and aerobic performance of coral reef fishes during experiments, 2009

Concerns about the impacts of ocean acidification on marine life have mostly focused on how reduced carbonate saturation affects calcifying organisms. Here, we show that levels of CO2-induced acidification that may be attained by 2100 could also have significant effects on marine organisms by reducing their aerobic capacity. The effects of temperature and acidification on oxygen consumption were tested in 2 species of coral reef fishes, Ostorhinchus doederleini and O. cyanosoma, from the Great Barrier Reef, Australia. The capacity for aerobic activity (aerobic scope) declined at temperatures above the summer average (29°C) and in CO2-acidified water (pH 7.8 and ~1000 ppm CO2) compared to control water (pH 8.15). Aerobic scope declined by 36 and 32% for O. doederleini and O. cyanosoma at temperatures between 29 to 32°C, whereas it declined by 33 and 47% for O. doederleini and O. cyanosoma in acidified water compared to control water. Thus, the declines in aerobic scope in acidified water were similar to those caused by a 3°C increase in water temperature. Minimum aerobic scope values of ~200 mg O2 kg-1 h-1 were attained for both species in acidified water at 32°C, compared with over 600 mg O2 kg-1 h-1 in control water at 29°C. Mortality rate increased sharply at 33°C, indicating that this temperature is close to the lethal thermal limit for both species. Acidification further increased the mortality rate of O. doederleini, but not of O. cyanosoma. These results show that coral reef fishes are sensitive to both higher temperatures and increased levels of dissolved CO2, and that the aerobic performance of some reef fishes could be significantly reduced if climate change continues unabated.学界对海洋酸化（ocean acidification）给海洋生物带来的影响，既往多聚焦于碳酸盐饱和度降低对钙化生物（calcifying organisms）的作用机制。本研究证实，到2100年可能达到的二氧化碳诱导酸化水平，还可通过降低海洋生物的有氧能力（aerobic capacity）对其产生显著负面影响。 我们以澳大利亚大堡礁（Great Barrier Reef）的两种珊瑚礁鱼类——Ostorhinchus doederleini与O. cyanosoma为实验对象，探究了温度与酸化对其耗氧量（oxygen consumption）的影响。结果显示，相较于对照组水体（pH 8.15），当水温超过夏季平均温度（29℃）或处于二氧化碳酸化水体（pH 7.8、CO₂浓度约1000 ppm）时，受试鱼类的有氧代谢范围（aerobic scope）均出现显著下降。 在29℃至32℃的水温区间内，Ostorhinchus doederleini与O. cyanosoma的有氧代谢范围分别下降36%与32%；而在酸化水体中，二者的有氧代谢范围较对照组分别下降33%与47%。由此可见，酸化水体引发的有氧代谢范围降幅，与水温升高3℃所导致的降幅基本相当。 在32℃的酸化水体中，两种鱼类的有氧代谢范围最低值约为200 mg O₂ kg⁻¹ h⁻¹；而在29℃的对照组水体中，其有氧代谢范围则超过600 mg O₂ kg⁻¹ h⁻¹。 当水温升至33℃时，受试鱼类的死亡率大幅上升，表明该温度接近两个物种的致死高温上限。酸化处理进一步提升了Ostorhinchus doederleini的死亡率，但对O. cyanosoma未产生显著影响。 上述研究结果表明，珊瑚礁鱼类对水温升高与溶解二氧化碳浓度增加均具有较高敏感性；若气候变化持续不受管控，部分珊瑚礁鱼类的有氧代谢性能将出现显著衰退。