Hypoxia is a widespread and increasing phenomenon in marine environments, including coral reefs. The bearded fireworm (Hermodice carunculata) is a large corallivorous amphinomid polychaete, with a high tolerance of environmental stress, including temperature, salinity, and dissolved oxygen (DO). Currently, little is known about the response of H. carunculata to chronic (≥ 18 h) hypoxia, although this knowledge is crucial to understand its impact on coral reef health under hypoxia scenarios. We tested the hypothesis that the number of branchial filaments (previously used as a diagnostic character for species identification) increases in response to chronic hypoxia. We subjected wild-caught fireworms to two levels of reduced DO (Mid: 4.5 ± 0.25 mg O2 L−1 and Low: 2.5 ± 0.25 mg O2 L−1) to explore their morphological and physiological responses to seven days of chronic hypoxia. Hypoxia exposure resulted in a higher number of branchial filaments (low = 57.2 ± 5.3, mid = 57.4 ± 6.1, and normal = 47.4 ± 11.2) after seven days. Fireworms exposed to hypoxia further reduced their rate of regeneration, but returned to normal regenerative rates after fifteen weeks under normoxic conditions. There was no difference in regeneration rates between low and mid DO groups. Our results demonstrate the importance of considering multiple physiological and morphological endpoints as well as phenotypic plasticity in species delimitations. Indeed, the results suggest that morphological variation can be indicative of environmental conditions.

中文翻译：

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对长须火虫 Hermodice carunculata (Annelida: Amphinomidae) 慢性缺氧的快速塑性反应

缺氧是包括珊瑚礁在内的海洋环境中普遍存在且日益严重的现象。胡须火虫 (Hermodice carunculata) 是一种大型的食珊瑚两栖类多毛类动物，对环境压力具有很高的耐受性，包括温度、盐度和溶解氧 (DO)。目前，关于 H. carunculata 对慢性（≥ 18 小时）缺氧的反应知之甚少，尽管这些知识对于了解其在缺氧情况下对珊瑚礁健康的影响至关重要。我们测试了鳃丝的数量（以前用作物种鉴定的诊断特征）的数量随着慢性缺氧而增加的假设。我们将野生捕获的火虫置于两个降低的 DO 水平（中：4.5 ± 0.25 mg O2 L−1 和低：2.5 ± 0。25 mg O2 L−1) 来探索它们对 7 天慢性缺氧的形态和生理反应。7 天后，缺氧暴露导致鳃丝数量增多（低 = 57.2 ± 5.3，中 = 57.4 ± 6.1，正常 = 47.4 ± 11.2）。暴露于缺氧的火虫进一步降低了它们的再生率，但在正常氧条件下十五周后恢复到正常的再生率。低溶解氧组和中溶解氧组之间的再生率没有差异。我们的结果证明了在物种划分中考虑多个生理和形态终点以及表型可塑性的重要性。事实上，结果表明形态变化可以指示环境条件。7 天后，缺氧暴露导致鳃丝数量增多（低 = 57.2 ± 5.3，中 = 57.4 ± 6.1，正常 = 47.4 ± 11.2）。暴露于缺氧的火虫进一步降低了它们的再生率，但在正常氧条件下十五周后恢复到正常的再生率。低溶解氧组和中溶解氧组之间的再生率没有差异。我们的结果证明了在物种划分中考虑多个生理和形态终点以及表型可塑性的重要性。事实上，结果表明形态变化可以指示环境条件。7 天后，缺氧暴露导致鳃丝数量增多（低 = 57.2 ± 5.3，中 = 57.4 ± 6.1，正常 = 47.4 ± 11.2）。暴露于缺氧的火虫进一步降低了它们的再生率，但在正常氧条件下十五周后恢复到正常的再生率。低溶解氧组和中溶解氧组之间的再生率没有差异。我们的结果证明了在物种划分中考虑多个生理和形态终点以及表型可塑性的重要性。事实上，结果表明形态变化可以指示环境条件。但在常氧条件下十五周后恢复正常再生率。低溶解氧组和中溶解氧组之间的再生率没有差异。我们的结果证明了在物种划分中考虑多个生理和形态终点以及表型可塑性的重要性。事实上，结果表明形态变化可以指示环境条件。但在常氧条件下十五周后恢复正常再生率。低溶解氧组和中溶解氧组之间的再生率没有差异。我们的结果证明了在物种划分中考虑多个生理和形态终点以及表型可塑性的重要性。事实上，结果表明形态变化可以指示环境条件。