Meiofauna Metabolism in Suboxic Sediments: Currently Overestimated |
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| Authors: | Ulrike Braeckman Jan Vanaverbeke Magda Vincx Dick van Oevelen Karline Soetaert |
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| Institution: | 1. Ghent University, Department of Biology, Marine Biology Research Group, Ghent, Belgium.; 2. Royal Netherlands Institute for Sea Research - NIOZ-Yerseke, Yerseke, The Netherlands.; Universidade Federal do Rio de Janeiro, Brazil, |
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| Abstract: | 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 (O2]) 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 O2], and (2) performed respiration measurements at a range of O2] conditions. The oxygen turnover model predicts a tight coupling between ambient O2] and meiofauna body O2] with oxygen within the body being consumed in seconds. This fast turnover favors long and slender organisms in sediments with low ambient O2] 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 O2], with Nematoda displaying the highest metabolic sensitivity for declining O2] followed by Foraminifera and juvenile Gastropoda. Ostracoda showed a behavioral stress response when ambient O2] reached a critical level. Reduced respiration at low ambient O2] 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. |
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