Ghent University, Department of Biology, Marine Biology Research Group, Ghent, Belgium.
PLoS One. 2013;8(3):e59289. doi: 10.1371/journal.pone.0059289. Epub 2013 Mar 28.
Oxygen is recognized as a structuring factor of metazoan communities in marine sediments. The importance of oxygen as a controlling factor on meiofauna (32 µm-1 mm in size) respiration rates is however less clear. Typically, respiration rates are measured under oxic conditions, after which these rates are used in food web studies to quantify the role of meiofauna in sediment carbon turnover. Sediment oxygen concentration ([O(2)]) is generally far from saturated, implying that (1) current estimates of the role of meiofauna in carbon cycling may be biased and (2) meiofaunal organisms need strategies to survive in oxygen-stressed environments. Two main survival strategies are often hypothesized: 1) frequent migration to oxic layers and 2) morphological adaptation. To evaluate these hypotheses, we (1) used a model of oxygen turnover in the meiofauna body as a function of ambient [O(2)], and (2) performed respiration measurements at a range of [O(2)] conditions. The oxygen turnover model predicts a tight coupling between ambient [O(2)] and meiofauna body [O(2)] with oxygen within the body being consumed in seconds. This fast turnover favors long and slender organisms in sediments with low ambient [O(2)] but even then frequent migration between suboxic and oxic layers is for most organisms not a viable strategy to alleviate oxygen limitation. Respiration rates of all measured meiofauna organisms slowed down in response to decreasing ambient [O(2)], with Nematoda displaying the highest metabolic sensitivity for declining [O(2)] followed by Foraminifera and juvenile Gastropoda. Ostracoda showed a behavioral stress response when ambient [O(2)] reached a critical level. Reduced respiration at low ambient [O(2)] implies that meiofauna in natural, i.e. suboxic, sediments must have a lower metabolism than inferred from earlier respiration rates conducted under oxic conditions. The implications of these findings are discussed for the contribution of meiofauna to carbon cycling in marine sediments.
氧气被认为是海洋沉积物中后生动物群落的结构因素。然而，氧气作为控制小型动物（32μm-1mm 大小）呼吸速率的因素的重要性尚不清楚。通常，呼吸速率是在有氧条件下测量的，然后在食物网研究中使用这些速率来量化小型动物在沉积物碳转化中的作用。沉积物中的氧气浓度([O2])通常远未饱和，这意味着 (1) 当前对小型动物在碳循环中作用的估计可能存在偏差，(2) 小型动物需要有策略在缺氧环境中生存。两种主要的生存策略通常被假设为：1）频繁迁移到有氧层，2）形态适应。为了评估这些假设，我们 (1) 使用了一个作为环境 [O2] 函数的后生动物体中的氧气周转模型，以及 (2) 在一系列 [O2] 条件下进行了呼吸测量。氧气周转模型预测环境 [O2] 和后生动物体 [O2] 之间存在紧密的耦合，体内的氧气在几秒钟内被消耗掉。这种快速的周转有利于在低环境 [O2] 的沉积物中具有长而细的生物体，但即使如此，对于大多数生物体来说，在缺氧和有氧层之间频繁迁移并不是缓解氧气限制的可行策略。所有测量的小型动物的呼吸速率都随着环境 [O2] 的降低而减慢，线虫对下降的 [O2] 表现出最高的代谢敏感性，其次是有孔虫和幼年腹足类。介形类动物在环境 [O2] 达到临界水平时表现出行为应激反应。在低环境 [O2] 下呼吸减少意味着自然（即缺氧）沉积物中的小型动物的新陈代谢必须比在有氧条件下进行的早期呼吸速率推断的要低。这些发现的影响将在海洋沉积物中后生动物对碳循环的贡献方面进行讨论。
