Copepod vital rates under CO2-induced acidification: a calanoid species and a cyclopoid species under short-term exposures

Although copepods have been considered tolerant against the direct influence of the ocean acidification (OA) projected for the end of the century, some recent studies have challenged this view. Here, we have examined the direct impact of short-term exposure to a pCO2/pH level relevant for the year 2100 (pHNBS, control: 8.18, low pH: 7.78), on the physiological performance of two representative marine copepods: the calanoid Acartia grani and the cyclopoid Oithona davisae. Adults of both species, from laboratory cultures, were preconditioned for four consecutive days in algal suspensions (Akashiwo sanguinea) prepared with filtered sea water pre-adjusted to the targeted pH values via CO2 bubbling. We measured the feeding and respiratory activity and reproductive output of those pre-conditioned females. The largely unaffected fatty acid composition of the prey offered between OA treatments and controls supports the absence in the study of indirect OA effects (i.e. changes of food nutritional quality). Our results show no direct effect of acidification on the vital rates examined in either copepod species. Our findings are compared with results from previous short- and long-term manipulative experiments on other copepod species.尽管此前学界普遍认为桡足类（copepods）对本世纪末预估的海洋酸化（Ocean Acidification, OA）直接影响具有耐受性，但近期多项研究对这一观点提出了挑战。本研究针对2100年对应水平的pCO₂/pH值（pH以NBS为计量基准，对照组pH为8.18，低pH组为7.78），探究了短期暴露对两种代表性海洋桡足类生理性能的直接影响：分别为哲水蚤类（calanoid）的格拉姆纺锤水蚤（*Acartia grani*）与剑水蚤类（cyclopoid）的达氏大眼剑水蚤（*Oithona davisae*）。实验所用两种桡足类的成体均来自实验室培养种群，先在经CO₂鼓泡预调节至目标pH值的过滤海水中制备的血红哈卡藻（*Akashiwo sanguinea*）悬浮液中连续预驯化4天。随后，我们测定了经预驯化的雌体的摄食活性、呼吸活性与繁殖产出。海洋酸化处理组与对照组所投喂饵料的脂肪酸组成无显著差异，这证实本研究未受海洋酸化间接效应的干扰（即食物营养品质的改变）。研究结果显示，海洋酸化对两种桡足类所检测的各项生命速率均无直接影响。我们将本研究的发现与此前针对其他桡足类开展的短期与长期操控实验结果进行了对比分析。