Growth characteristics of massive corals from the Great Barrier Reef

Annual density banding in massive coral skeletons provides a means to date and retrospectively analyse coral growth and geochemical composition. Annual density bands, consisting of high and low density skeleton are revealed when a slice from a coral is X-rayed. Analysis of these annual density bands enables the calculation of the following annual growth characteristics: average skeletal density, linear extension rate and calcification rate.The living tissue layer occupies a discrete layer at the outer edge of coral colonies. The thickness of the living tissue layer is an indication of the "health" of the coral colony and has been shown to decrease in thickness with environmental stress.This dataset contains skeletal density, extension rate, calcification rate and tissue thickness measurements for long and short massive Porites coral cores as well as whole Porites colonies from the Great Barrier Reef.The purpose of this research is to investigate variation in growth characteristics for massive corals along environmental gradients. [Temporal, spatial scales]Sample Processing:1. Coral CoresCoral cores are mounted on metal trays and three slices ~7mm thick are removed using a solvent cleaned diamond tipped blade on an electric saw. Each slice is X-rayed at a commercial radiographers and a positive print made of the X-ray. An assessment is made to choose the best slice for further analysis. This is based on the clarity of the annual density bands visible in the X-ray positive, as well as the overall quality of the core.An optimum track for density analyses, chosen to cross the clearest presentation of annual density bands along the length of the core, is marked on the X-ray positive.Density is measured along each marked track with a gamma densitometer with a 4mm diameter gamma-ray beam. The gamma count, measured at 0.0254cm intervals, combined with the known thickness of the coral core slice provided absolute skeletal density (in g.cm3) at that point on the core slice. A data series of absolute density vs. distance is produced for each coral core slice. On the Great Barrier Reef, skeleton of highest density forms during the summer season of highest water temperature and the low-density band forms in the winter season of coolest water temperature.Successive density peaks are then dated backwards from the date of collection. This then allows for the calculation of annual extension rate (mm/y) and annual calcification rate (gCaCO3/cm2/y).2. Whole Porites Colonies.Colonies are cut vertically into halves with a chainsaw fitted with a masonry blade. One half of the colony is placed on the moveable bed of a circular saw and at least two 6-7cm slices are removed from vertical planes close to the centre of the whole colony. Further processing is similar to that of core slices, except that two tracks are chosen for density analysis. Both tracks start at the origin of the colony, with one track close to the vertical growth axis and the other close to the horizontal axis.All coral slices, remaining parts of each core or colony and X-rays are archived at AIMS.This database has been superseded by newer methods of analysis, described in De'ath AG, Lough JM and Fabricius KE (2009) Declining coral calcification on the Great Barrier Reef. Science. 323: 116-119, and found on record "Coral Calcification In Massive Porites Of The Great Barrier Reef, Over A 400 Year Period" linked below.

大型珊瑚骨骼的年密度带为珊瑚生长与地球化学组成的定年及回溯分析提供了可行手段。当对珊瑚切片进行X射线扫描时，会显现出由高密度与低密度骨骼构成的年密度带。对这些年密度带的分析可用于计算以下年度生长特征：平均骨骼密度、线性延伸速率与钙化速率。
活组织层是位于珊瑚群落外缘的一层离散组织，其厚度可反映珊瑚群落的“健康状态”，且已有研究表明其厚度会随环境胁迫降低。
本数据集包含来自大堡礁（Great Barrier Reef）的长、短大型滨珊瑚（Porites）岩芯，以及完整滨珊瑚群落的骨骼密度、延伸速率、钙化速率与组织厚度测量数据。本研究旨在探究大型珊瑚的生长特征沿环境梯度的变化规律。[时间、空间尺度]
样本处理：
1. 珊瑚岩芯
将珊瑚岩芯固定于金属托盘上，使用经溶剂清洁的金刚石刀片（在电动锯上操作）切取3片厚度约7mm的切片。将每片切片送至商业放射机构进行X射线扫描，并制作X射线正片。根据X射线正片中可见的年密度带清晰度以及岩芯整体质量，评估并选取最佳切片用于后续分析。在X射线正片上标记一条最优分析轨迹，使其穿过岩芯长度方向上年密度带最清晰的区域。
使用直径为4mm的伽马射线束伽马密度计（gamma densitometer）沿每条标记轨迹测量密度。以0.0254cm的间隔测量伽马计数，结合珊瑚岩芯切片的已知厚度，即可计算出该切片对应位置的绝对骨骼密度（单位：g·cm⁻³）。每个珊瑚岩芯切片均可生成绝对密度随距离变化的数据集。在大堡礁海域，骨骼高密度层形成于水温最高的夏季，而低密度带则形成于水温最低的冬季。
随后以采样日期为基准，对连续出现的密度峰值进行反向定年，由此可计算出年度延伸速率（单位：mm·a⁻¹）与年度钙化速率（单位：gCaCO₃·cm⁻²·a⁻¹）。
2. 完整滨珊瑚群落
使用装配有砖石刀片的链锯将完整群落垂直切割为两半。将其中一半放置于圆锯的可移动工作台上，从靠近群落中心的垂直平面切取至少2片6~7cm厚的切片。后续处理流程与岩芯切片类似，但需选取两条分析轨迹：两条轨迹均始于群落原点，一条靠近垂直生长轴，另一条靠近水平生长轴。
所有珊瑚切片、各岩芯或群落的剩余部分以及X射线底片均存档于澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）。
本数据库已被更新的分析方法取代，相关研究见于De'ath AG、Lough JM与Fabricius KE（2009）发表于《科学》（Science）的论文《大堡礁滨珊瑚钙化率下降》（Declining coral calcification on the Great Barrier Reef），刊载于《科学》323卷：116-119，此外还可通过下方链接获取题为《大堡礁大型滨珊瑚400年尺度的钙化情况》（Coral Calcification In Massive Porites Of The Great Barrier Reef, Over A 400 Year Period）的相关记录。