Luminescent lines in massive Porites corals from the Great Barrier Reef as proxies for mainland runoff

Massive Porites colonies were collected from 1 reef in the Coral Sea and 29 reefs located along the length and across the width of the Great Barrier Reef (GBR), between November 1987 and May 1992. The reefs were located within the following regions: Northern Coral Sea (Ashmore Reef); Northern GBR (Lagoon Reef, Eel Reef, Portland Roads, Rocky Island, Night Island, Reef No. 13-055 and Reef No. 13-050); Cairns to Cape Melville (Tydeman Reef, Pipon Island, Flinders Island, Watson Island, South Petherbridge Island, Two Isles, Boulder Reef, East Hope Island, Undine Reef, Snapper Island, Batt Reef, and Double Island); Mission Beach (Stephens Island and Bedarra Island); Central GBR (Myrmidon Reef, Rib Reef and Pandora Reef); Southern GBR (Shaw Island, Reef No. 20-200, Credlin Reef, Reef No. 21-141 and Middle Percy Island). All colonies were between 0.2 and 0.5 m in height and were selected from similar environments towards the rear of the windward reef flat or on sheltered parts of fringing reefs in the lee of the islands at depths between 3 and 5 m relative to mean low water spring tide levels. Between six and 15 colonies were collected from each site and 232 similar sized colonies were used for luminescence analysis. The species of coral colonies analysed were: Porites lutea, Porites lobata, Porites australensis, Porites solida and Porites mayeri.Colonies were cut in half vertically and at least 2 slices, approximately 7mm thick, were cut from the centre of each colony. Coral growth characteristics had been recorded from these slices using X-ray and densitometry in a previous study and slices were dated using the annual density banding patterns and gamma density traces. Each dated year represents the time between successive density peaks.Slices were viewed under UV light in a darkened room. Luminescence was assessed along 2 tracks close to the vertical growth axis and 1 horizontal track. For each slice and year the appearance of the luminescent lines was graded visually into one of four categories: 0 = no visible line, 1 = faint luminescent line, 2 = moderate luminescent line and 3 = intense luminescent line. A luminescence index was derived for each year that 2 or more colonies from the same reef were analysed. The index for a particular year and reef was the sum of the number of luminescent lines in each category multiplied by the value of that category, divided by the total number of colonies.Daily river flows were obtained from the Queensland Department of Natural Resources for the 9 major rivers that drain into the GBR lagoon: Normanby River, Daintree River, Barron River, North Johnstone River, South Johnstone River, Tully River, Herbert River, Burdekin River and Fitzroy River.A 3-D hydrodynamic model of the movement of freshwater river plumes from the Burdekin River was used to provide daily salinity variations at Rib and Pandora Reefs for the period 1966-1986. Measures of salinity derived for each reef were: average annual salinity; minimum daily salinity; number of days with salinity < 35 ppt; sum of daily salinity values < 35 ppt; and average of daily salinities < 35 ppt. Reefs were classified as inshore, midshelf and offshore. In addition, the linear distance (km) between each reef and the nearest mainland was estimated and expressed as a percentage of the shelf width at that latitude. The average water depth between each reef and the nearest point on the mainland was calculated from depths at taken at approximately 225 m intervals from a bathymetry data model for the GBR. This study was undertaken to determine:1. if luminescent signals in corals are reproducible2. how far offshore luminescent lines are evident and if there is a relationship between intensity of luminescence and distance from shore3. how often are reefs affected by freshwater4. if past flows for rivers other than the Burdekin can be reconstructed from luminescent lines in massive corals5. if luminescent lines in corals from the central GBR match 3-D modeling of salinities associated with the Burdekin River plume. These colonies (with the exception of those collected from Ashmore Reef) were initially collected to determine variations in growth characteristics in massive corals with environmental gradients.See Metadata Record: Environmental controls on growth of massive Porites corals from the Great Barrier Reef

1987年11月至1992年5月期间，研究团队从珊瑚海的1处礁体以及沿大堡礁（Great Barrier Reef, GBR）南北延展、东西横跨的29处礁体，采集了大型滨珊瑚属（Porites）珊瑚群落。所有采样礁体分布于以下区域：北部珊瑚海区域（阿什莫尔礁）；大堡礁北部区域（潟湖礁、鳗礁、波特兰路礁、罗基岛礁、奈特岛礁、13-055号礁与13-050号礁）；凯恩斯至梅尔维尔角区域（泰德曼礁、皮蓬岛礁、弗林德斯岛礁、沃森岛礁、南佩瑟布里奇岛礁、双岛礁、博尔德礁、东霍普岛礁、安丁礁、斯纳珀岛礁、巴特礁与双岛礁）；使命海滩区域（斯蒂芬斯岛礁与贝达拉岛礁）；大堡礁中部区域（默米登礁、里布礁与潘多拉礁）；大堡礁南部区域（肖岛礁、20-200号礁、克雷德林礁、21-141号礁与中珀西岛礁）。
所有采集的珊瑚群落高度介于0.2至0.5米之间，均选自相似生境：迎风礁坪后部，或岛屿背风侧岸礁的隐蔽区域，采样水深相对于大潮平均低潮位为3至5米。每个采样点采集6至15个珊瑚群落，最终共有232个尺寸相近的群落用于发光特性分析。
本次分析的珊瑚群落所属物种为：团块滨珊瑚（Porites lutea）、叶状滨珊瑚（Porites lobata）、澳大利亚滨珊瑚（Porites australensis）、坚实滨珊瑚（Porites solida）与迈耶滨珊瑚（Porites mayeri）。
将珊瑚群落沿垂直方向对半切开，从每个群落的中心部位切取至少2片厚度约7毫米的切片。过往研究已通过X射线与光密度分析法，从上述切片中记录了珊瑚生长特性；本次研究通过年度密度条带模式与伽马密度曲线对切片进行定年，每个定年年份对应两次连续密度峰值之间的时段。
在暗室中利用紫外光观察切片。沿垂直生长轴附近的2条轨迹与1条水平轨迹评估发光特性。针对每片切片与对应年份，将发光条带的外观通过目视分级为4类之一：0级=无可见条带，1级=微弱发光条带，2级=中等发光条带，3级=强烈发光条带。
针对同一礁体采集且数量≥2个群落的分析年份，可计算得到发光指数。某一特定年份与礁体对应的发光指数，为各等级发光条带的数量乘以其等级分值后的总和，再除以该采样点的总群落数。
研究从昆士兰州自然资源部获取了注入大堡礁潟湖的9条主要河流的日径流量数据，分别为：诺曼比河、丹特里河、巴伦河、北约翰斯通河、南约翰斯通河、塔利河、赫伯特河、伯德金河与菲茨罗伊河。
本研究采用伯德金河淡水羽流运动三维水动力模型，获取了1966至1986年期间里布礁与潘多拉礁的日盐度变化数据。为每个礁体计算的盐度指标包括：年平均盐度、日最低盐度、盐度＜35‰的天数、盐度＜35‰的日累计值，以及盐度＜35‰的日平均盐度。
将所有礁体划分为近岸、陆架中部与远岸三类。此外，估算了每个礁体至最近大陆的直线距离（千米），并以该纬度处陆架宽度的百分比表示；同时基于大堡礁水深数据模型，以约225米的间隔采集水深数据，计算得到每个礁体至最近大陆点的平均水深。
本研究旨在明确以下5个科学问题：1. 珊瑚中的发光信号是否具有可重复性；2. 发光条带可在多远的远岸区域被观测到，且发光强度与离岸距离之间是否存在关联；3. 礁体受淡水影响的频率如何；4. 是否可通过大型滨珊瑚群落的发光条带重建伯德金河以外其他河流的历史径流量；5. 大堡礁中部区域珊瑚的发光条带是否与伯德金河淡水羽流的盐度三维模拟结果相匹配。本次采集的珊瑚群落（阿什莫尔礁采样群落除外）最初是为了探究环境梯度下大型滨珊瑚的生长特性变化。
详见元数据记录：《大堡礁大型滨珊瑚生长的环境调控机制》