Photophysiological stress in response to short-term sedimentation in scleractinian corals of the Great Barrier Reef

Effects of short-term sedimentation on common coastal coral species were investigated in laboratory and field experiments on the Great Barrier Reef using pulse-amplitude modulated (PAM) chlorophyll fluorometry. In the laboratory, changes in maximal quantum yields of photosystem II (Fv/Fm) in Montipora peltiformis were examined in response to the amount of sedimentation (mg cm-²) and duration of exposure (h). Field experiments compared susceptibilities of common coastal coral species to sedimentation through examination of quantum yields.Fragments of the foliose coral M. peltiformis were sampled from 3 to 5 m water depth at Magnetic Island. Fine, muddy sediment was collected from 3 m water depth near the AIMS jetty and its carbon, nitrogen, and phosphorous levels ascertained. Corals in tanks were exposed to sediments which were stirred and allowed to settle before controls were reintroduced.Photosynthetic activity was determined by measuring variable chlorophyll fluorescence of photosystem II (PS II), with a pulse-amplitude modulated chlorophyll fluorometer. In dark acclimated corals, maximal quantum yield was calculated as the ratio of variable to maximum fluorescence (Fv/Fm). Fifteen measurements, evenly distributed over the surface, were made on each fragment.Sediment load was calculated by normalising the amount of sediment (dry weight) retrieved from each coral fragment normalised to its surface area (determined by tracing the coral outline onto paper, cutting and weighing the paper, then using a calibration curve to convert paper weight to surface area).Subsamples of the corals were analysed for zooxanthellae densities and chlorophyll (chl a and chl c2) concentrations. Two subsamples were counted under the microscope using a haemocytometer slide (8 replicates) and counts were normalised to coral surface area for zooxanthellae densities.Sediment-loaded and control fragments were removed from the tank after 0, 12, 18, 24, and 36 h and 2-5 replicates were analysed for each treatment and time. Recovery from sedimentation was monitored for up to 7 days by repeated measurements of maximum PS II quantum yields of M. peltiformis fragments, which had been exposed to sediment for 0, 12, 18, and 24 h.To determine the effects of sedimentation on adjacent tissue, sediment was applied to about 50% of the surface of 4 colonies of M. peltiformis (the remaining surface was left clean). After 48 h exposure, maximum quantum yields of the clean surfaces and those along the edge of the sediment patch, were measured and compared with those of the colonies before sediment application. The experiment was repeated on 4 colonies each of Echinopora lamellosa and massive Porites (exposed for 22 h before measurement of effective quantum yield).Sediment was added to 12 common coastal species of scleractinian corals at 6¿8 m depth on the coastal reefs PAM and chlorophyll fluorometry measurements were taken to assess the effects of 22 h of sediment loading on the effective yields. Responses were assessed between reefs and between species. The study aimed to investigate the short-term stress reaction of the coral Montipora peltiformis to sediment exposure and its potential to recover from such stress under controlled laboratory conditions, particularly, the effects of exposure to different amounts of sediment for different lenths of time on photosynthetic activity, zooxanthellae count, and chlorophyll concentration.To assess the susceptibility of a range of coral species to sediment stress in the field. To contribute to understanding about the damage to corals caused by short-term exposure to high levels of sedimentation and potential shifts in community structure in relation to prolonged or repeated enhanced levels of sedimentation in coastal reefs of the Great Barrier Reef. Reef locations: Hay Island and Wilkie Island (northern Great Barrier Reef), and Green Island and Normandy Island (central Great Barrier Reef).Echinopora lamellosa, Fungia crassa, Galaxea fascicularis, Montipora crassituberculata, Montipora danae, Montipora tuberculosa, Merulina scabricula, Pachyseris speciosa, Pectina lacuca, massive Porites, Turbinaria peltata, Turbinaria reniformis

本研究于大堡礁（Great Barrier Reef）开展室内与原位野外实验，借助脉冲振幅调制（pulse-amplitude modulated, PAM）叶绿素荧光仪，探究短期沉积作用对常见沿岸造礁珊瑚物种的影响。室内实验环节：针对盾形管孔珊瑚（Montipora peltiformis）的光系统II（photosystem II, PS II）最大量子产额（Fv/Fm）变化，分析其与沉积负荷（单位：mg·cm⁻²）及暴露时长（单位：h）的响应关系。野外实验则通过检测量子产额，对比常见沿岸珊瑚物种对沉积胁迫的耐受差异。样本采集：盾形管孔珊瑚的珊瑚片段采集于磁岛（Magnetic Island）水深3~5 m的海域。细颗粒泥质沉积物采自澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）码头附近水深3 m的海域，并测定其碳、氮、磷含量。实验水族箱中的珊瑚先暴露于经搅拌沉降处理的沉积物，随后再设置空白对照组。光合活性测定方法：光合活性通过脉冲振幅调制叶绿素荧光仪检测光系统II的可变叶绿素荧光值表征。对暗适应的珊瑚样本，其最大量子产额以可变荧光与最大荧光的比值（Fv/Fm）计算。每个珊瑚片段的表面均匀布设15个测量点，完成荧光检测。沉积负荷计算方式：将每个珊瑚片段上附着的沉积物干重标准化为单位表面积沉积量，表面积通过将珊瑚轮廓描记于纸张，裁剪后称重，再通过校准曲线将纸张重量转换为表面积得到。珊瑚亚样品分析：采集珊瑚亚样品用于分析虫黄藻（zooxanthellae）密度及叶绿素（叶绿素a与叶绿素c₂）浓度。其中2份亚样品通过血细胞计数板（haemocytometer）在显微镜下计数，设置8个技术重复，并将计数结果标准化为单位表面积的虫黄藻密度，以表征种群丰度。实验处理与恢复监测：分别在0、12、18、24、36 h时将负载沉积物的珊瑚片段与对照组取出，每个处理组与时间节点设置2~5个生物学重复。针对经0、12、18、24 h沉积物暴露的盾形管孔珊瑚片段，通过重复检测其光系统II最大量子产额，监测其长达7 d的沉积胁迫恢复过程。相邻组织影响实验：为探究沉积作用对珊瑚相邻组织的影响，研究者将沉积物涂抹于4株盾形管孔珊瑚约50%的表面（其余区域保持清洁）。暴露48 h后，检测清洁区域及沉积物斑块边缘区域的最大量子产额，并与沉积物施加前的菌落量子产额进行对比。该实验同样在4株片状棘珊瑚（Echinopora lamellosa）与块状多孔珊瑚（massive Porites）上重复开展，暴露时长为22 h，随后检测其有效量子产额。野外大型实验：研究者在PAM礁与沿岸礁的6~8 m水深区域，向12种常见沿岸石珊瑚（scleractinian corals）物种施加沉积物，通过检测叶绿素荧光值，评估22 h沉积物负载对其有效量子产额的影响。分析不同礁区及不同珊瑚物种间的响应差异。研究目标：本研究旨在明确盾形管孔珊瑚在受控室内条件下，暴露于沉积物胁迫后的短期应激反应及恢复潜力，重点解析不同沉积负荷与暴露时长对其光合活性、虫黄藻密度及叶绿素浓度的影响；同时评估多种珊瑚物种在野外环境下对沉积胁迫的耐受差异，以期阐明大堡礁沿岸海域短期高浓度沉积暴露对珊瑚造成的损伤，以及长期或反复增强的沉积作用如何影响沿岸珊瑚群落结构。实验礁区：本实验的礁区包括北大堡礁的海伊岛（Hay Island）与威尔基岛（Wilkie Island），以及中大海礁的格林岛（Green Island）与诺曼底岛（Normandy Island）。实验涉及的12种石珊瑚物种依次为：片状棘珊瑚（Echinopora lamellosa）、厚壳珊瑚（Fungia crassa）、丛生盔形珊瑚（Galaxea fascicularis）、粗瘤管孔珊瑚（Montipora crassituberculata）、达纳管孔珊瑚（Montipora danae）、疣状管孔珊瑚（Montipora tuberculosa）、粗糙梅花孔珊瑚（Merulina scabricula）、美丽厚丝珊瑚（Pachyseris speciosa）、凹穴梳状珊瑚（原文疑似笔误为Pectina lacuca，标准学名为Pectinia lacunosa）、块状多孔珊瑚（massive Porites）、盾形陀螺珊瑚（Turbinaria peltata）、肾形陀螺珊瑚（Turbinaria reniformis）