DEFINING NUTRITIONAL BOTTLENECKS OF REEF CORAL GROWTH AND STRESS TOLERANCE

在地球上最具魅力和多样性的生态系统中，珊瑚礁仅在5亿人口中维持了超过25%的海洋生物多样性<1% of ocean surface area and the livelihoods of >。然而，建造栖息地的珊瑚极易受到人为变化的影响。研究得最多的是海洋变暖对珊瑚礁构成的威胁。对自然营养环境的扰动也代表着存在的危险，但为什么会这样呢？这个问题由来已久。在查尔斯·达尔文的开创性观察之后的175年多，我们仍然缺乏令人信服的机械解释，为什么珊瑚礁在营养贫乏的海洋地区蓬勃发展，维持异常高的生物生产率。答案当然是植根于细胞内微藻（“虫黄藻”）和珊瑚动物宿主之间的共生关系，但所涉及的生理过程还远未被理解。最近的实地研究从根本上反驳了现有的共生功能模型，表明珊瑚的大部分营养物质来自水柱溶解无机氮（DIN）和磷（DIP），但在珊瑚动物中没有已知的机制。我们的工作（试点研究结果）表明，珊瑚“吃草”的共生种群，DIN和DIP转移到主机提供了一种新的机制。我们建议通过在十个代表性的造礁物种中测试放牧假说来改变我们对全球珊瑚营养循环和共生关系的理解，我们将：（i）在受控的长期实验中，通过（15 N）同位素标记和元素分析记录共生体放牧对DIN和DIP的吸收和利用。ii）量化共生体放牧与动物园饲养的营养结合效率，并比较对珊瑚生长和压力耐受性的影响。iii）确定当前和预测未来的海洋温度和pH值如何影响溶解无机营养素的利用，并塑造珊瑚生长和共生功能。我们还将开展广泛的影响促进活动，包括知识转移研讨会。在这次活动中，我们将把珊瑚礁管理和政策制定方面的利益相关者与珊瑚礁营养生物学、空间生态学和生物地球化学建模方面的领先专家聚集在一起，将我们的研究结果转化为政策制定者和珊瑚礁管理的建议。

Among the most charismatic and diverse ecosystems on Earth, coral reefs sustain >25% of all marine biodiversity in only <1% of ocean surface area and the livelihoods of >0.5 billion people. Yet the habitat-building corals are acutely vulnerable to anthropogenic change. Best studied are the threats posed to coral reefs by ocean warming. Perturbations to the natural nutrient environment also represent an existential danger, but why is this the case? This question has old origins. More than 175 years after Charles Darwin's seminal observation, we still lack a convincing mechanistic explanation as to why reef corals thrive, sustaining exceptionally high rates of biological production, in nutrient-poor oceanic regions. The answer is certainly rooted in the symbiotic association between endocellular microalgae ("zooxanthellae") and the coral animal host but the physiological processes involved are far from understood. Recent field studies fundamentally contradict existing models for symbiosis functioning by suggesting that corals source most of their nutrients from the water column as dissolved inorganic nitrogen (DIN) and phosphorus (DIP) but there is no known mechanism for such a process in coral animals. Our work (pilot study results herein) suggests that corals "graze" on their symbiont population, providing a novel mechanism for DIN and DIP transfer to the host. We propose to transform our understanding of nutrient cycling and symbiosis in corals worldwide by testing the grazing hypothesis in ten representative reef-building species.We will: (i) Document DIN and DIP uptake and utilisation by symbiont-grazing through (15N) isotopic labelling and elemental analysis in controlled long-term experiments. ii) Quantify the efficiency of nutrient incorporation by symbiont-grazing versus zooplankton-feeding and compare the resulting effects on coral growth and stress tolerance. iii) Determine how present-day and projected future ocean temperature and pH influence the utilisation of dissolved inorganic nutrients and shape coral growth and symbiosis functioning.We will also undertake a broad range of impact-promoting activities including a knowledge transfer workshop. For this event, we will bring stakeholders in coral reef management and policy development together with leading specialists in coral reef nutrient biology, spatial ecology and biogeochemical modelling to translate our findings into advice for policy makers and coral reef management.