Growth performance and survival of larval Atlantic herring, under the combined effects of elevated temperatures and CO2

In the coming decades, environmental change like warming and acidification will affect life in the ocean. While data on single stressor effects on fish are accumulating rapidly, we still know relatively little about interactive effects of multiple drivers. Of particular concern in this context are the early life stages of fish, for which direct effects of increased CO2 on growth and development have been observed. Whether these effects are further modified by elevated temperature was investigated here for the larvae of Atlantic herring (Clupea harengus), a commercially important fish species. Over a period of 32 days, larval survival, growth in size and weight, and instantaneous growth rate were assessed in a crossed experimental design of two temperatures (10°C and 12°C) with two CO2 levels (400 μatm and 900 μatm CO2) at food levels mimicking natural levels using natural prey. Elevated temperature alone led to increased swimming activity, as well as decreased survival and instantaneous growth rate (Gi). The comparatively high sensitivity to elevated temperature in this study may have been influenced by low food levels offered to the larvae. Larval size, Gi and swimming activity were not affected by CO2, indicating tolerance of this species to projected "end of the century" CO2 levels. A synergistic effect of elevated temperature and CO2 was found for larval weight, where no effect of elevated CO2 concentrations was detected in the 12°C treatment, but a negative CO2 effect was found in the 10°C treatment. Contrasting CO2 effects were found for survival between the two temperatures. Under ambient CO2 conditions survival was increased at 12°C compared to 10°C. In general, CO2 effects were minor and considered negligible compared to the effect of temperature under these mimicked natural food conditions. These findings emphasize the need to include biotic factors such as energy supply via prey availability in future studies on interactive effects of multiple stressors.

未来数十年间，海洋变暖与酸化等环境变化将对海洋生物的生存造成影响。当前，有关单一胁迫因子对鱼类影响的研究数据正快速累积，但我们对多重驱动因子的交互效应仍知之甚少。在此背景下，鱼类的早期生活阶段尤其值得关注——已有研究发现，CO₂浓度升高会对其生长与发育产生直接影响。本研究以具有重要商业价值的大西洋鲱（Clupea harengus）幼鱼为对象，探究了升温是否会进一步改变CO₂升高所带来的效应。实验采用双因素交叉设计，设置10℃、12℃两个温度梯度以及400 μatm、900 μatm两个CO₂分压水平，并以天然猎物模拟自然食物供给水平，在为期32天的实验周期内，对幼鱼的存活率、体长体重增长及瞬时生长率（Gi）进行了评估。单独的升温处理会提升幼鱼的游泳活性，同时降低其存活率与瞬时生长率（Gi）。本研究中幼鱼对升温的较高敏感性，可能受到实验投喂食物水平偏低的影响。CO₂浓度升高并未对幼鱼体长、瞬时生长率及游泳活性造成显著影响，表明该物种对本世纪末预计的CO₂浓度水平具有耐受性。研究发现升温与CO₂升高对幼鱼体重存在协同效应：在12℃处理组中未检测到CO₂浓度升高的显著影响，但在10℃处理组中观测到了CO₂升高带来的负面效应。两种温度条件下幼鱼存活率对CO₂的响应存在显著差异：在环境本底CO₂条件下，12℃组的存活率高于10℃组。总体而言，在模拟自然食物条件下，相较于温度的影响，CO₂的效应较为微弱，可忽略不计。本研究结果强调，在未来开展多重胁迫因子交互效应的相关研究时，需纳入猎物可获得性等与能量供给相关的生物因子。