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.

大型珊瑚骨骼的年度密度带，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途径。通过对珊瑚切片进行X射线扫描，可显现出由高密度与低密度骨骼构成的年度密度带。对这些年度密度带进行分析，可计算得到以下年度生长特征参数：平均骨骼密度、线性延伸速率与钙化速率。

活组织层呈离散薄层分布于珊瑚群体的外缘。活组织层厚度可反映珊瑚群体的健康状态，已有研究表明其厚度会随环境胁迫而降低。

本数据集包含取自大堡礁的长、短型大型滨珊瑚（Porites）岩芯，以及完整滨珊瑚群体的骨骼密度、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]

1. 珊瑚岩芯处理
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（电动锯）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。基于X射线正片上可见的年度密度带清晰度与岩芯整体质量，评估并选取最适合后续分析的切片。在X射线正片上标记出一条最优分析轨迹，该轨迹需穿过岩芯全长上最清晰的年度密度带分布区域。
使用直径为4mm的伽马射线束的伽马密度计（gamma densitometer），沿每条标记轨迹测量密度。以0.0254cm的间隔采集伽马计数数据，结合珊瑚岩芯切片的已知厚度，即可得到该切片上对应点位的绝对骨骼密度（单位：g·cm⁻³）。为每片珊瑚岩芯切片生成绝对密度随距离变化的数据集序列。在大堡礁海域，高密度骨骼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，反向定年连续出现的密度峰值，由此可计算得到年度延伸速率（单位：mm·a⁻¹）与年度钙化速率（单位：gCaCO₃·cm⁻²·a⁻¹）。

2. 完整滨珊瑚群体处理
使用搭载砖石刀片的链锯将完整珊瑚群体垂直切为两半。将其中一半固定于圆锯的可移动工作台，从靠近群体中心的垂直平面切取至少2片厚度为6~7cm的切片。后续处理流程与岩芯切片一致，但需选取两条轨迹进行密度分析。两条轨迹均起始于群体生长原点，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、岩芯或群体的剩余部分以及X射线底片均存档于澳大利亚海洋科学研究所（AIMS）。

本数据集已被更新的分析方法取代，相关方法参见De'ath AG、Lough JM与Fabricius KE于2009年发表于《科学》（Science）杂志的论文《大堡礁珊瑚钙化衰退》（323卷：116-119页），以及存档记录中题为《大堡礁400年尺度大型滨珊瑚钙化情况》的数据集（链接见下文）。