Calcium carbonate (CaCO 3 ) sediments are the dominant form of CaCO 3 on coral reefs accumulating in lagoon and inter-reefal areas. Owing to their mineralogy and a range of physical parameters, tropical CaCO 3 sediments are predicted to be more sensitive to dissolution driven by ocean acidification than the skeleton of living reef organisms. How this scales up to impact infaunal organisms, which are an important food source for higher trophic levels, and thereby ecosystem functioning, is not well explored. We combined seasonal field surveys in a shallow-reef lagoon ecosystem on the Great Barrier Reef, Australia, with stable isotope analyses and a tank-based experiment to examine the potential top-down influence of the deposit-feeding sea cucumber, Stichopus herrmanni , on this infaunal community under current and future ocean pH. Densities of surface-sediment meiofauna were lowest in winter and spring, with harpacticoid copepods (38%) and nematodes (27%) the dominant taxa. Stable isotope analyses showed that S. herrmanni had a top-down influence on meiofauna and microphytes with a distinct δ 13 C and δ 15 N trophic position that was homogenous across seasons and locations. Tanks that mimicked sandy shallow-reef lagoon habitats were used to examine the effects of ocean acidification (elevated p CO 2 ) on this trophic interaction. We used outdoor control (sediment only) and experimental (sediment plus S. herrmanni ) tanks maintained at present-day and near-future p CO 2 (+ 570 µatm) for 24 days, which fluctuated with the diel p CO 2 cycle. In sediment-only tanks, copepods were > twofold more abundant at elevated p CO 2 , with no negative effects documented for any meiofauna group. When included in the community, top-down control by S. herrmanni counteracted the positive effects of low pH on meiofaunal abundance. We highlight a novel perspective in coral reef trophodynamics between surface-sediment meiofauna and deposit-feeding sea cucumbers, and posit that community shifts may occur in shallow-reef lagoon habitats in a future ocean with implications for the functioning of coral reefs from the bottom up.

中文翻译：

---

热带浅礁泻湖栖息地当前和未来的营养相互作用

碳酸钙 (CaCO 3 ) 沉积物是在泻湖和珊瑚礁间区域积累的珊瑚礁上 CaCO 3 的主要形式。由于它们的矿物学和一系列物理参数，预计热带 CaCO 3 沉积物对海洋酸化驱动的溶解比活珊瑚礁生物的骨架更敏感。这如何扩大以影响底层生物，它们是较高营养水平的重要食物来源，从而影响生态系统功能，尚未得到很好的探索。我们将澳大利亚大堡礁浅礁泻湖生态系统的季节性实地调查与稳定同位素分析和基于罐的实验相结合，以检查以沉积物为食的海参 Stichopus herrmanni 对这个在当前和未来海洋 pH 值下的动物群落。表层沉积物小型动物的密度在冬季和春季最低，其中棘状桡足类 (38%) 和线虫 (27%) 是主要分类群。稳定同位素分析表明，S. herrmanni 对小型动物群和微型植物具有自上而下的影响，具有不同的 δ 13 C 和 δ 15 N 营养位置，在不同季节和地点都是同质的。模拟沙质浅礁泻湖栖息地的水箱用于检查海洋酸化（p CO 2 升高）对这种营养相互作用的影响。我们使用室外控制（仅沉积物）和实验（沉积物加 S. herrmanni ）罐在当前和近期维持 p CO 2 (+ 570 µatm) 24 天，随着 diel p CO 2 循环波动。在只有沉积物的水箱中，桡足类在 p CO 2 升高时的数量增加了两倍以上，没有记录对任何小型动物群的负面影响。当包括在社区中时，S. herrmanni 自上而下的控制抵消了低 pH 值对小型动物丰度的积极影响。我们强调了表层沉积物小型动物和以沉积物为食的海参之间珊瑚礁营养动力学的新观点，并假设未来海洋的浅礁泻湖栖息地可能发生群落变化，这对珊瑚礁自下而上的功能产生影响.