Gobler Christopher J, Baumann Hannes
School of Marine and Atmospheric Sciences, Stony Brook University, Southampton, NY 11968, USA
Department of Marine Sciences, University of Connecticut, Groton, CT 06340, USA.
Biol Lett. 2016 May;12(5). doi: 10.1098/rsbl.2015.0976.
There is increasing recognition that low dissolved oxygen (DO) and low pH conditions co-occur in many coastal and open ocean environments. Within temperate ecosystems, these conditions not only develop seasonally as temperatures rise and metabolic rates accelerate, but can also display strong diurnal variability, especially in shallow systems where photosynthetic rates ameliorate hypoxia and acidification by day. Despite the widespread, global co-occurrence of low pH and low DO and the likelihood that these conditions may negatively impact marine life, very few studies have actually assessed the extent to which the combination of both stressors elicits additive, synergistic or antagonistic effects in marine organisms. We review the evidence from published factorial experiments that used static and/or fluctuating pH and DO levels to examine different traits (e.g. survival, growth, metabolism), life stages and species across a broad taxonomic spectrum. Additive negative effects of combined low pH and low DO appear to be most common; however, synergistic negative effects have also been observed. Neither the occurrence nor the strength of these synergistic impacts is currently predictable, and therefore, the true threat of concurrent acidification and hypoxia to marine food webs and fisheries is still not fully understood. Addressing this knowledge gap will require an expansion of multi-stressor approaches in experimental and field studies, and the development of a predictive framework. In consideration of marine policy, we note that DO criteria in coastal waters have been developed without consideration of concurrent pH levels. Given the persistence of concurrent low pH-low DO conditions in estuaries and the increased mortality experienced by fish and bivalves under concurrent acidification and hypoxia compared with hypoxia alone, we conclude that such DO criteria may leave coastal fisheries more vulnerable to population reductions than previously anticipated.
人们越来越认识到，在许多沿海和公海环境中，低溶解氧（DO）和低pH值条件同时存在。在温带生态系统中，这些条件不仅会随着温度升高和代谢率加快而季节性出现，而且还可能表现出强烈的昼夜变化，特别是在浅海系统中，光合作用率在白天可缓解缺氧和酸化情况。尽管全球范围内低pH值和低溶解氧普遍同时出现，而且这些条件可能对海洋生物产生负面影响，但实际上很少有研究评估这两种压力源的组合在多大程度上对海洋生物产生相加、协同或拮抗作用。我们回顾了已发表的析因实验证据，这些实验使用静态和/或波动的pH值和溶解氧水平，来研究广泛分类范围内的不同性状（如生存、生长、代谢）、生命阶段和物种。低pH值和低溶解氧组合的相加负面影响似乎最为常见；然而，也观察到了协同负面影响。目前，这些协同影响的发生情况和强度都无法预测，因此，酸化和缺氧同时发生对海洋食物网和渔业的真正威胁仍未得到充分了解。要填补这一知识空白，需要在实验和实地研究中扩展多压力源方法，并建立一个预测框架。考虑到海洋政策，我们注意到沿海水域的溶解氧标准在制定时未考虑同时存在的pH值水平。鉴于河口地区持续存在低pH值-低溶解氧同时出现的情况，以及与单独缺氧相比，鱼类和双壳贝类在酸化和缺氧同时发生时死亡率增加，我们得出结论，这样的溶解氧标准可能会使沿海渔业比以前预期的更容易受到种群数量减少的影响。
