Seeded Acropora digitifera corals survive best on wave-exposed reefs with grazing from small fishes

In a 16-month field study, we deployed aquaria-reared Acropora digitifera spat on engineered coral seeding devices across 10 sites spanning a wave-energy gradient at Moore Reef (Great Barrier Reef, Australia). Two devices were used to investigate the role of grazing: a fish-exclusion device and a featureless control.Mature gravid Acorpora digitifera (Dana 1846) colonies were collected from Moore Reef ahead of coral spawning in February 2022. The corals were transported back to the Australian Institute of Marine Science National Sea Simulator (SeaSim) facility and kept in temperature controlled outdoor aquaria. Gamete bundles were collected, separated, washed and fertilized, then the embryos were transferred to indoor larval rearing tanks where they remained until they reached settlement competency after 5-6 days. Conditioned concrete tabs (14 × 14 mm2; developed under the Reef Restoration and Adaptation Program) were used as settlement substrates. The plugs contained a mixed community of crustose coralline algae and bacteria biofilms that are known to induce settlement of Acorpora corals; these were conditioned in aquaria for 2-months prior to settlement and the corals were held in aquaria (temperature control, flow through, no light, mixed feed of microalage and enriched rotifers) for 2-months after settlement. Corals were seeded to 10 sites on Moore Reef in May 2022. The field deployment followed a hierarchical design including location (n=1), sites (n=10), experimental plots (n=25, 2 devices per plot), device type (n=2, featureless control and a fish exclusion device), contrete settlement tabs (n=3 per device), and coral spat (n=> 5 per tab) . Devices were deployed to the reef crest (3-5 m depth, high tide) and fixed in experimental plots with a cable tie in an upright, horizontal position. Devices and their fixings were removed after 16 months.Data were collected at six timepoints and included quantitative and qualitative assessments to determine the influence of biological (fish abundance and grazing, benthic composition) and environmental (wave energy) drivers on coral growth and survival. Assessments were categorised and analysed by spatial scale. Bayesian hierarchical logistic mixed-effects regression models, principal component and redundancy analyses were used to interogate the data.

本研究开展了一项为期16个月的野外调查，在澳大利亚大堡礁穆尔礁沿波浪能梯度设置的10个研究点位上，部署了搭载室内水族箱培育的指形鹿角珊瑚（Acropora digitifera）幼体的工程化珊瑚播种装置。本研究采用两种装置开展放牧作用相关实验：分别为鱼类排除装置与无特征对照装置。2022年2月珊瑚产卵前，我们从穆尔礁采集了成熟怀卵的指形鹿角珊瑚（Acropora digitifera，Dana 1846）群落。随后将这些珊瑚转运至澳大利亚海洋科学研究所国家海洋模拟系统（National Sea Simulator, SeaSim）设施中，置于温控室外水族箱内暂养。研究人员收集配子束，经分离、清洗与受精后，将胚胎转移至室内幼体培育槽中，培育5至6天后幼体达到附着变态所需的发育状态。经生物预处理的混凝土贴片（尺寸14×14 mm²，由珊瑚修复与适应计划研发）被用作附着基质。该贴片表面携带有壳状珊瑚藻与细菌生物膜的混合群落，这类群落已被证实可诱导鹿角珊瑚附着；研究人员将贴片在水族箱中预处理2个月后用于珊瑚附着，附着完成后的幼体则在水族箱中暂养2个月，暂养条件为温控、流水、无光，并以微藻与强化轮虫作为混合饵料。2022年5月，我们将培育好的珊瑚幼体接种至穆尔礁的10个研究点位。本次野外部署采用分层实验设计，包含以下层级：研究区域（n=1）、研究点位（n=10）、实验样地（n=25，每个样地设置2台装置）、装置类型（n=2，分别为无特征对照装置与鱼类排除装置）、混凝土附着贴片（每台装置配备3片贴片）以及珊瑚幼体（每片贴片接种不少于5只幼体）。装置被部署于礁脊区域（水深3至5米，高潮位），并用扎带将装置以直立水平的方式固定于实验样地中。部署16个月后，回收所有装置及其固定配件。本研究共设置6个采样时间点，采集的数据包含定量与定性两类评估指标，用于解析生物因子（鱼类丰度与放牧压力、底栖生物组成）与环境因子（波浪能）对珊瑚生长与存活的影响。所有评估工作均按空间尺度进行分类与分析。研究采用贝叶斯分层逻辑混合效应回归模型、主成分分析与冗余分析对数据进行解析。