Seawater carbonate chemistry and protein content, respiration, symbiodinium densities, survivorship of Pocillopora damicornis larvae in a laboratory experiment

Efforts to evaluate the response of coral larvae to global climate change (GCC) and ocean acidification (OA) typically employ short experiments of fixed length, yet it is unknown how the response is affected by exposure duration. In this study, we exposed larvae from the brooding coral Pocillopora damicornis to contrasts of temperature (24.00 °C [ambient] versus 30.49 °C) and pCO2 (49.4 Pa versus 86.2 Pa) for varying periods (1-5 days) to test the hypothesis that exposure duration had no effect on larval response as assessed by protein content, respiration, Symbiodinium density, and survivorship; exposure times were ecologically relevant compared to representative pelagic larval durations (PLD) for corals. Larvae differed among days for all response variables, and the effects of the treatment were relatively consistent regardless of exposure duration for three of the four response variables. Protein content and Symbiodinium density were unaffected by temperature and pCO2, but respiration increased with temperature (but not pCO2) with the effect intensifying as incubations lengthened. Survival, however, differed significantly among treatments at the end of the study, and by the 5th day, 78% of the larvae were alive and swimming under ambient temperature and ambient pCO2, but only 55-59% were alive in the other treatments. These results demonstrate that the physiological effects of temperature and pCO2 on coral larvae can reliably be detected within days, but effects on survival require > or = 5 days to detect. The detection of time-dependent effects on larval survivorship suggests that the influence of GCC and OA will be stronger for corals having long PLDs.

全球气候变化（Global Climate Change, GCC）与海洋酸化（Ocean Acidification, OA）对珊瑚幼虫的响应评估研究，通常采用固定时长的短期实验方案，但目前尚未明确暴露时长如何影响其响应。本研究以育幼型珊瑚多孔鹿角珊瑚（*Pocillopora damicornis*）的幼虫为实验对象，设置温度（24.00 ℃[环境对照] vs 30.49 ℃）与pCO2（49.4 Pa vs 86.2 Pa）的梯度处理，并设置1至5天的不同暴露时长，以验证“暴露时长对以蛋白质含量、呼吸速率、虫黄藻（Symbiodinium）密度及存活率为指标的幼虫响应无影响”的假说；所选暴露时长与珊瑚典型浮游幼虫期（pelagic larval durations, PLD）具有生态学相关性。

所有响应指标均随培养天数出现显著差异，且四项响应指标中有三项的处理效应不受暴露时长的显著影响。蛋白质含量与虫黄藻密度不受温度及pCO2的影响，但呼吸速率随温度升高而上升（不受pCO2影响），且该效应随培养时长延长而增强。但存活率在实验结束时各处理组间存在显著差异：至第5天时，环境对照（常温常pCO2）下有78%的幼虫仍存活并可游动，而其余处理组的存活率仅为55%~59%。

本研究结果表明，温度与pCO2对珊瑚幼虫的生理效应可在数天内被可靠检测，但对存活率的效应则需要≥5天才能被观测到。幼虫存活率的时间依赖性效应提示，全球气候变化与海洋酸化对拥有较长浮游幼虫期的珊瑚的影响将更为显著。