RAPID: A Unique Cruise Opportunity to Test the Effect of Trace Metal Limitation on Oxidative Stress and Coral Bleaching

智力上的功绩。自20世纪80年代以来，珊瑚漂白的频率、严重程度和地理范围都急剧增加，预计这一趋势将继续下去，对热带地区造成重大的环境和经济影响。这种漂白或珊瑚失去其光合作用内共生甲藻(Zooxanthellae；Symbioddium spp.)，似乎是由于高光强下温度升高引起的氧化应激增加所致。然而，这种失败背后的机制尚不清楚。PIs目前的项目名为“微量金属限制对虫黄藻氧化应激的影响及其在珊瑚漂白中的作用”(OCE-0648478)的前提是，虫黄藻抗氧化防御系统的必要上调受到低浓度的溶解铁、锌和铜；抗氧化酶功能所必需的金属(铜、锌、锰和铁-超氧化物歧化酶；过氧化氢酶[铁]；抗坏血酸过氧化物酶[铁])的限制。实验室和野外操作实验的结果表明，在高温(但不是低)温度和光照强度下限制珊瑚宿主对铁和铜/锌的有效性确实可以显著降低栖息地共生体的光合作用效率和ROS酶活性，同时增加其光系统的非光合作用猝灭；这两个指标都表明了漂白条件的开始。然而，尽管在每个实验中都有很高的完整性，他们发现这种模式并不符合所有的珊瑚群体。根据有限的采样，从外陆架区域采集的珊瑚通常(但不总是)在金属有效性下降的情况下表现出氧化胁迫的迹象，而在近岸采集的珊瑚或保存在沿海流动海水中(溶解金属浓度较高)的珊瑚往往没有什么明显的影响。海洋浮游植物文献中对过量金属的吸收和储存有很好的描述，这表明珊瑚金属暴露的历史是一个关键因素，无论是对我们的实验还是对观察到的珊瑚漂白的分布都是如此。私人投资机构有一个独特的、意想不到的机会来检验这一假设，他们加入了澳大利亚海洋科学研究所前往弗林德斯礁的研究邮轮；弗林德斯礁是珊瑚海的一个离岸环礁，与我们之前的研究地点相比，它距离零星的陆地金属输入要远得多。他们将参加这次邮轮，在甲板上进行孵化，测试降低和略微升高的铁、铜、锌和锰浓度对珊瑚光合作用效率、ROS酶活性、共生体色素组成以及ROS酶和其他基因表达的影响。这个地理位置将提供一个理想的测试地点，以验证他们发现的金属对虫黄藻氧化应激的影响，并确定导致热带水域日益频繁和严重的珊瑚漂白事件的一些关键机制和营养因素。广泛的影响：该项目将为两名研究生和一名初级女性博士科学家提供一个独特的研究机会，她们将把这项工作的各个方面用于论文和职业发展。这项研究解决了珊瑚漂白控制的根本未知问题，珊瑚漂白是对热带国家海洋生物多样性和经济稳定的主要威胁之一。这些发现将为实验室和现场开发的假说提供关键测试，这些假说是痕量金属限制作为虫黄藻及其珊瑚宿主-珊瑚漂白的前驱-氧化应激的贡献者所起的作用。将开发一系列针对K-12高年级学生和本科生的模块化讲座和演示，并将纳入缅因州大学现有的海洋科学推广计划和本科生课程。虫黄藻和珊瑚之间的光养共生，以及它被物理环境因素破坏，为化学、物理和生物学的整合提供了一个内在强大的案例研究，这将向海洋科学本科生说明在定量物理科学方面需要严格的培训。这些发现将为影响漂白事件严重性的因素提供关键见解，并可能提出现实的缓解策略，以将局部环境或经济敏感地区的漂白事件降至最低。

Intellectual Merit. Coral bleaching has increased dramatically in frequency, severity, and geographic extent since the 1980's and this trend is anticipated to continue, causing major environmental and economic impacts in tropical regions. This bleaching, or loss by corals of their photosynthetic endosymbiotic dinoflagellates (zooxanthellae; Symbiodinium spp.), appears to result from increased oxidative stress arising from the combined effects of elevated temperature at high light intensities. However, the mechanisms underlying this failure are not understood. The premise of the PIs' current project entitled "Effects of Trace Metal Limitation on Oxidative Stress in Zooxanthellae and Its Role in Coral Bleaching" (OCE - 0648478) is that the necessary up-regulation of zooxanthellae antioxidant defenses is restricted by low concentrations of dissolved Fe, Zn and Cu; metals essential for antioxidant enzyme function (Cu, Zn-, Mn-, and Fe-SOD; catalase [Fe]; ascorbate peroxidase [Fe]). Findings from their laboratory and field manipulation experiments show that restricting Fe, and Cu/Zn availability to coral hosts under high (but not low) temperature and light intensity indeed can significantly decrease both photosynthetic efficiency of symbionts in-hospite and ROS enzyme activities, while increasing non-photosynthetic quenching of their photosystems; each indicators of the onset of bleaching conditions. However, although there is high integrity within each experiment, they have found this pattern is not consistent with all coral colonies. Based on limited sampling, it appears that corals collected from the outer shelf region normally (but not always) display indications of oxidative stress under conditions of decreased metal availability, while those collected nearshore, or maintained in coastally-derived flowing seawater (where dissolved metal concentrations are higher), often show little discernable effect. Excess metal uptake and storage is well described in the marine phytoplankton literature, which suggests that the history of the coral metal exposure is a critical factor, both with respect to our experiments as well as to the distribution of coral bleaching observed. The PIs have an unique and unforeseen opportunity to test this hypothesis by joining an Australian Institute for Marine Sciences research cruise to Flinders Reef; an offshore atoll in the Coral Sea that is substantially more distant from sporadic terrestrial metal inputs that our previous study sites. They will participate in this cruise to run on-deck incubations testing the effect of reduced and marginally elevated Fe, Cu, Zn and Mn concentrations on coral photosynthetic efficiency, ROS enzyme activities, symbiont pigment composition, and ROS enzyme and other gene expression. This geographical site will provide the ideal test site for verifying their findings of metal effects on oxidative stress in zooxanthellae, and identify some of the key mechanisms and nutritional factors contributing to the increasingly frequent and severe coral bleaching events in tropical waters.Broader Impacts: This project will provide a unique research opportunity for two graduate students and a junior female Ph.D. scientist, who will use aspects of the work for their thesis and career development. The research addresses the fundamental unknowns of the controls of coral bleaching, one of the leading threats to marine biodiversity and economic stability of tropical nations. The findings will provide a key test of laboratory- and field-developed hypotheses of the role of trace metal limitation as a contributor to oxidative stress of zooxanthellae and their coral hosts; a precursor to coral bleaching. A modular series of lectures and demonstrations targeting both upper K-12 and undergraduates will be developed and will be incorporated into existing outreach programs and undergraduate courses in Marine Science at the University of Maine. The phototrophic symbiosis between zooxanthellae and corals, and its disruption by physical environmental factors, provides an inherently powerful case study for the integration of chemistry, physics, and biology that will illustrate to marine science undergraduates the need for rigorous training in the quantitative physical sciences. The findings will provide key insights to the factors that influence the severity of bleaching events, and possibly suggest realistic mitigation strategies to minimize bleaching events in localized environmentally or economically sensitive regions.