Department of Oceanography, Texas A&M University, College Station, Texas, USA.
University of Wisconsin-Madison, Madison, Wisconsin, USA.
Appl Environ Microbiol. 2022 May 10;88(9):e0034722. doi: 10.1128/aem.00347-22. Epub 2022 Apr 18.
In July 2016, a severe coral reef invertebrate mortality event occurred approximately 200 km southeast of Galveston, Texas, at the East Flower Garden Bank, wherein ∼82% of corals in a 0.06-km area died. Based on surveys of dead corals and other invertebrates shortly after this mortality event, responders hypothesized that localized hypoxia was the most likely direct cause. However, no dissolved oxygen data were available to test this hypothesis, because oxygen is not continuously monitored within the Flower Garden Banks sanctuary. Here, we quantify microbial plankton community diversity based on four cruises over 2 years at the Flower Garden Banks, including a cruise just 5 to 8 days after the mortality event was first observed. In contrast with observations collected during nonmortality conditions, microbial plankton communities in the thermocline were differentially enriched with taxa known to be active and abundant in oxygen minimum zones or that have known adaptations to oxygen limitation shortly after the mortality event (e.g., SAR324, , , and MGII). Unexpectedly, these enrichments were not localized to the East Bank but were instead prevalent across the entire study area, suggesting there was a widespread depletion of dissolved oxygen concentrations in the thermocline around the time of the mortality event. Hydrographic analysis revealed the southern East Bank coral reef (where the localized mortality event occurred) was uniquely within the thermocline at this time. Our results demonstrate how temporal monitoring of microbial communities can be a useful tool to address questions related to past environmental events. In the northwestern Gulf of Mexico in July 2016, ∼82% of corals in a small area of the East Flower Garden Bank coral reef suddenly died without warning. Oxygen depletion is believed to have been the cause. However, there was considerable uncertainty, as no oxygen data were available from the time of the event. Microbes are sensitive to changes in oxygen and can be used as bioindicators of oxygen loss. In this study, we analyze microbial communities in water samples collected over several years at the Flower Garden Banks, including shortly after the mortality event. Our findings indicate that compared to normal conditions, oxygen depletion was widespread in the deep-water layer during the mortality event. Hydrographic analysis of water masses further revealed some of this low-oxygen water likely upwelled onto the coral reef.
2016 年 7 月，在德克萨斯州加尔维斯顿东南约 200 公里处的东花园区发生了一次严重的珊瑚礁无脊椎动物死亡事件，在 0.06 公里的区域内，约有 82%的珊瑚死亡。根据此次死亡事件后不久对死亡珊瑚和其他无脊椎动物的调查，应对人员假设局部缺氧是最有可能的直接原因。然而，由于花园区保护区内没有连续监测氧气，因此没有溶解氧数据来验证这一假设。在这里，我们根据两年内四次在花园区的考察，基于微生物浮游生物群落多样性进行了量化，其中包括在首次观察到死亡事件后 5 至 8 天进行的一次考察。与在非死亡条件下收集的观察结果相比，在温跃层中，微生物浮游生物群落以在低氧区中活跃和丰富的分类群或在死亡事件后不久具有对氧气限制的已知适应性的分类群（例如，SAR324， ， ，和 MGII）为特征的差异丰富。出乎意料的是，这些富集并没有局限于东海岸，而是在整个研究区域内普遍存在，这表明在死亡事件发生时，温跃层中的溶解氧浓度普遍下降。水文分析显示，南部东海岸珊瑚礁（局部死亡事件发生的地方）此时恰好处于温跃层中。我们的结果表明，对微生物群落的时间监测如何成为解决与过去环境事件相关问题的有用工具。2016 年 7 月，在墨西哥湾西北部，东花园区珊瑚礁的一个小区域内，约 82%的珊瑚突然毫无预警地死亡。据信，氧气枯竭是造成这种情况的原因。然而，由于事件发生时没有可用的氧气数据，因此存在相当大的不确定性。微生物对氧气变化敏感，可用作氧气损失的生物指标。在这项研究中，我们分析了在花园区收集的多年水样中的微生物群落，包括在死亡事件发生后不久。我们的研究结果表明，与正常情况相比，在死亡事件期间，深水区的氧气消耗更为广泛。水团的水文分析进一步表明，部分低氧水可能上升到珊瑚礁上。
