Seawater carbonate chemistry and Amphiprion melanopus activity during experiments, 2011

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.

珊瑚礁面临的两大核心威胁为持续升高的海水表面温度（sea surface temperature, SST）与海洋酸化，二者均源于大气二氧化碳（CO₂）浓度的不断上升。近期研究证据表明，水体温度升高与溶解态CO₂浓度上升均可改变鱼类行为，进而降低个体适合度，但二者的交互效应尚未明确。本研究采用全因子实验设计，探究温度（设置3个水平：28.5、30、31.5 °C）与二氧化碳分压（pCO₂，设置3个水平：均值分别为420、530与960 µatm）对幼体海葵鱼（Amphiprion melanopus, Bleeker 1852）的摄食量与活动水平的独立效应及交互效应。实验设置的环境条件与当前海洋现状以及基于大气CO₂排放预测的本世纪中期、末期海洋环境保持一致。将同窝幼鱼从幼虫阶段末期开始，在9种实验处理体系中饲养21天，随后开展行为观测。结果显示，在最高温度处理组中，幼鱼的摄食量与觅食活动均出现下降。单独分析CO₂水平的效应时，其并未对行为产生显著影响，但二者存在显著交互效应：当仅在高温（31.5 °C）结合对照浓度（420 µatm）或中等浓度（530 µatm）CO₂环境中饲养时，幼鱼的摄食量与觅食活动会降低；而当高温环境搭配高浓度CO₂（960 µatm）时，上述行为指标反而出现上升。若食物同化与生长的热最适条件已被突破，那么在高温与高CO₂环境中维持摄食量与觅食活动可能会降低能量利用效率；同时，维持较高的觅食投入可能会提升被捕食风险。本研究结果表明，到本世纪末期，海水表面温度升高与CO₂浓度上升的交互效应所引发的觅食行为变化，可能会对礁区幼鱼的生长与存活产生显著影响。