Seawater carbonate chemistry and Amphiprion melanopus activity during experiments, 2011@en

Two of the major threats to coral reefs are increasing sea surface temperature and ocean acidification, both of which result from rising concentrations of atmospheric carbon dioxide (CO2). Recent evidence suggests that both increased water temperature and elevated levels of dissolved CO2 can change the behaviors of fishes in ways that reduce individual fitness, however the interacting effects of these variables are unknown. We used a fully factorial experiment to test the independent and interactive effects of temperature (3 levels: 28.5, 30, and 31.5 °C) and pCO2 (3 levels: averaging 420, 530, and 960 µatm) on food consumption and activity level of juvenile anemonefish Amphiprion melanopus (Bleeker 1852). Experimental levels were consistent with current-day ocean conditions and predictions for mid-century and late-century based on atmospheric CO2 projections. Sibling fish were reared for 21 days from the end of their larval phase in each of the nine treatments, at which time behavioral observations were conducted. Food consumption and foraging activity decreased at the highest temperature. In isolation, CO2 level did not significantly affect behavior; however, there was an interaction with temperature. While rearing at high temperature (31.5 °C) and control (420 µatm) or moderate (530 µatm) CO2 resulted in a reduction of food consumption and foraging activity, rearing at high temperature and high CO2 (960 µatm) resulted in an elevation in these behaviors. Maintaining food consumption and foraging activity in high temperature and CO2 conditions may reduce energy efficiency if the thermal optimum for food assimilation and growth has been exceeded. Maintaining foraging effort might increase predation vulnerability. These results suggest that changes in foraging behaviors caused by the interactive effects of increased SST and CO2 could have significant effects on the growth and survival of juvenile reef fishes by late century.珊瑚礁面临的两大主要威胁分别是日益升高的海表温度（Sea Surface Temperature, SST）与海洋酸化，二者均由大气中二氧化碳（carbon dioxide, CO₂）浓度攀升所引发。现有研究证据表明，水温升高与溶解态二氧化碳（dissolved CO₂）浓度提升均会改变鱼类行为，进而降低个体适合度（fitness），但目前学界对这两个变量的交互效应仍尚不明确。本研究采用完全析因实验（fully factorial experiment）设计，探究温度（设置3个梯度：28.5、30、31.5 ℃）与分压二氧化碳（partial pressure of CO₂, pCO₂，设置3个梯度：平均420、530、960 µatm）对幼体海葵鱼（juvenile anemonefish）黑双锯鱼（*Amphiprion melanopus*, Bleeker 1852）的摄食量与活动水平的独立效应与交互效应。实验设置的浓度梯度与当前海洋环境、基于大气二氧化碳预测的本世纪中叶及末叶海洋环境预测值相符。将同窝幼鱼从仔鱼阶段末期开始，在9种实验处理中分别饲养21天，随后开展行为观察实验。在最高温度梯度下，幼鱼的摄食量与觅食活动均有所下降。单独来看，二氧化碳浓度并未对鱼类行为产生显著影响，但二者与温度存在显著交互效应：当幼鱼在高温（31.5 ℃）与对照浓度二氧化碳（420 µatm）或中等浓度二氧化碳（530 µatm）条件下饲养时，其摄食量与觅食活动均出现下降；而当幼鱼在高温与高浓度二氧化碳（960 µatm）条件下饲养时，上述行为指标反而有所提升。如果食物同化与生长的温度最适范围已被突破，那么在高温与高二氧化碳环境下维持摄食量与觅食活动，可能会降低能量利用效率。维持较高的觅食投入则可能提升幼鱼被捕食的风险。本研究结果表明，到本世纪末，海表温度升高与二氧化碳浓度上升的交互效应所引发的觅食行为改变，可能会对礁栖幼鱼的生长与存活产生显著影响。