Experimental ocean acidification alters the allocation of metabolic energy

Energy is required to maintain physiological homeostasis in response to environmental change. Although responses to environmental stressors frequently are assumed to involve high metabolic costs, the biochemical bases of actual energy demands are rarely quantified. We studied the impact of a near-future scenario of ocean acidification [800 µatm partial pressure of CO2 (pCO2)] during the development and growth of an important model organism in developmental and environmental biology, the sea urchin Strongylocentrotus purpuratus. Size, metabolic rate, biochemical content, and gene expression were not different in larvae growing under control and seawater acidification treatments. Measurements limited to those levels of biological analysis did not reveal the biochemical mechanisms of response to ocean acidification that occurred at the cellular level. In vivo rates of protein synthesis and ion transport increased 50% under acidification. Importantly, the in vivo physiological increases in ion transport were not predicted from total enzyme activity or gene expression. Under acidification, the increased rates of protein synthesis and ion transport that were sustained in growing larvae collectively accounted for the majority of available ATP (84%). In contrast, embryos and prefeeding and unfed larvae in control treatments allocated on average only 40% of ATP to these same two processes. Understanding the biochemical strategies for accommodating increases in metabolic energy demand and their biological limitations can serve as a quantitative basis for assessing sublethal effects of global change. Variation in the ability to allocate ATP differentially among essential functions may be a key basis of resilience to ocean acidification and other compounding environmental stressors.

生物需消耗能量以维持生理稳态，从而应对环境变化。尽管环境压力刺激引发的反应通常被认为涉及高额代谢成本，但实际能量需求的生化基础却鲜有量化研究。本研究以发育与环境生物学领域的重要模式生物——紫球海胆（Strongylocentrotus purpuratus）为对象，探究了近未来海洋酸化情景[CO₂分压（pCO₂）为800微大气压（µatm）]对其发育与生长过程的影响。在对照组与海水酸化处理组中，幼虫的体型、代谢率、生化成分及基因表达均无显著差异。若仅局限于上述生物分析层面的测量，则无法揭示细胞水平上应对海洋酸化的生化机制。酸化条件下，幼虫体内蛋白质合成与离子转运速率提升了50%。值得注意的是，离子转运的体内生理活性提升无法通过总酶活性或基因表达数据预测。酸化环境中，生长阶段幼虫维持的蛋白质合成与离子转运速率提升，共同消耗了84%的可用ATP（占大部分）。相比之下，对照组中的胚胎、预摄食期及未摄食幼虫平均仅将40%的ATP分配至这两个过程。解析生物适应代谢能量需求增加的生化策略及其生物学限制，可为评估全球变化的亚致死效应提供定量依据。生物在必需功能间差异化分配ATP的能力差异，或许是其应对海洋酸化及其他复合环境压力的韧性核心基础。