Studying carbon dynamics in the coral holobiont provides essential knowledge of nutritional strategies and is thus central to understanding coral ecophysiology. In this study, we assessed the carbon budget in Pocillopora damicornis (using HCO3) as a function of feeding status and temperature stress. We also compared dissolved oxygen (O2) fluxes measured at the colony scale and at the polyp scale. At both scales, O2 production rates were enhanced for fed vs. unfed corals, and unfed corals exhibited higher bleaching and reduced photosynthetic activity at high temperature. Unfed corals exclusively respired autotrophically acquired carbon, while fed corals mostly respired heterotrophically acquired carbon. As a consequence, fed corals excreted on average >5 times more organic carbon than unfed corals. Photosynthate translocation was higher under thermal stress, but most of the carbon was lost via respiration and/or mucus release (42−46% and 57−75% of the fixed carbon for unfed and fed corals, respectively). Such high loss of translocated carbon, coupled to low assimilation rates in the coral tissue and symbionts, suggests that P. dami cornis was nitrogen and/or phosphorus limited. Heterotrophy might thus cover a larger portion of the nutritional demand for P. damicornis than previously assumed. Our results suggest that active feeding plays a fundamental role in metabolic dynamics and bleaching susceptibility of corals.

中文翻译：

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温度和摄食对 Pocillopora damicornis 碳收支和 O2 动态的影响

研究珊瑚全生物中的碳动力学提供了营养策略的基本知识，因此是理解珊瑚生态生理学的核心。在这项研究中，我们评估了 Pocillopora damicornis（使用 HCO3）作为摄食状态和温度压力的函数的碳收支。我们还比较了在菌落规模和息肉规模上测量的溶解氧 (O2) 通量。在这两个尺度上，喂食珊瑚与未喂食珊瑚的 O2 生产率均提高，并且未喂食珊瑚在高温下表现出更高的漂白和降低的光合活性。未喂食的珊瑚只呼吸自养获得的碳，而喂食的珊瑚主要呼吸异养获得的碳。因此，喂食的珊瑚比未喂食的珊瑚排出的有机碳平均多出 5 倍以上。在热应激下光合物质易位较高，但大部分碳通过呼吸和/或粘液释放损失（分别为未喂食和喂食珊瑚固定碳的 42-46% 和 57-75%）。如此高的易位碳损失，加上珊瑚组织和共生体的低同化率，表明 P. damicornis 受氮和/或磷限制。因此，异养可能比以前假设的大米蠵虫的营养需求占更大的部分。我们的结果表明，主动摄食在珊瑚的代谢动力学和白化敏感性中起着重要作用。再加上珊瑚组织和共生体的低同化率，表明 P. damicornis 受氮和/或磷限制。因此，异养可能比以前假设的大米蠵虫的营养需求占更大的部分。我们的结果表明，主动摄食在珊瑚的代谢动力学和白化敏感性中起着重要作用。再加上珊瑚组织和共生体的低同化率，表明 P. damicornis 受氮和/或磷限制。因此，异养可能比以前假设的大米蠵虫的营养需求占更大的部分。我们的结果表明，主动摄食在珊瑚的代谢动力学和白化敏感性中起着重要作用。