Temporal dynamics in coral bioindicators for water quality on coastal coral reefs of the Great Barrier Reef

Temporal variation in a range of coral bioindicators was examined for 2 years on a coastal coral reef of the Great Barrier Reef.Coral and water samples were collected in June, September and October 2005 (Year 1, Dry Season); February, March and April 2006 (Year 1, Wet Season); July, September and October 2006 (Year 2, Dry Season); and March, April and May 2007 (Year 2, Wet Season) at each of the 3 locations (Horseshoe Bay, Davies and Broadhurst Reefs.Loggers measured turbidity (nephelometric turbidity units, NTU) and benthic irradiance (photosynthetically active radiation, PAR, 400-700 nm) every 10 min (comprising 20 measurements integrated over 10 s).Surface water was sampled at each of 2 sites within each location during each sampling event to measure chlorophyll a, phaeophytin, particulate nitrogen (PN), particulate phosphorus (PP), particulate organic carbon (POC), dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved organic nutrients (DON and DOP) and total suspended solids (TSS). A water quality index (WQI, derived from the sum of z-score transformations for the water column nutrient variables) was calculated for each season using sites and sampling events as replicates.Apical branches (~6 cm long) of Pocillopora damicornis were collected from the centre of each of 6 colonies during each sampling event. Physiological parameters analysed included determinations of symbiont density (from 8 replicate counts), chlorophyll a and skeletal density (determined as the ratio between dry weight and buoyant weight).Sea surface temperature (SST), surface irradiance (µmol photons m-² s-1) and wind speed (m s-1), all recorded at half-hour intervals, were obtained from automatic weather stations (AWS) operated by the Australian Institute of Marine Science in Cleveland Bay and Davies Reef. From this weather data, mean SST, mean total daily surface irradiance (¿mol photons m-² day-1) and mean wind speed (m s-1) were calculated for the 14 days preceding each sampling event. Mean wind speed from Cleveland Bay was used to provide an indication of the effects of wave height, and hence resuspension of sediments. Total monthly rainfall from May 2005 to May 2007 for the Townsville region was obtained from the Bureau of Meteorology.This research aimed to quantify temporal changes in environmental parameters and develop potential stress thresholds for turbidity and test the hypothesis that variations in environmental conditions can be measured as a response in coral bioindicators. To investigate the significance of the relationships between bioindicators and environmental parameters and assess their specificity to changes in water quality.This research project was jointly funded by the Catchmentto-Reef Cooperative Research Centre (a supplementary program to the Cooperative Research Centre of the Great Barrier Reef World Heritage Area -‘‘CRC Reef’’, and the Rainforest CRC), and the Australian Institute of Marine Science. We thank Glenn De’ath for help with the statistical analyses, Michelle Skuza and Margaret Wright for processing the nutrient and chlorophyll samples. The manuscript was improved by constructive comments from Jon Brodie and the anonymous reviewers. The satellite image was gratefully provided by Ken Rohde (Department of Natural Resources and Water, Queensland).

本研究针对大堡礁（Great Barrier Reef）近岸珊瑚礁的一系列珊瑚生物指标（coral bioindicators），开展了为期2年的时间变化特征调查。

珊瑚与水样采集于2005年6月、9月、10月（第1年旱季）、2006年2月、3月、4月（第1年雨季）、2006年7月、9月、10月（第2年旱季）及2007年3月、4月、5月（第2年雨季），采样点共3处：马蹄湾（Horseshoe Bay）、戴维斯礁（Davies Reef）、布罗德赫斯特礁（Broadhurst Reefs）。记录仪每10分钟测量一次浊度（散射浊度单位 nephelometric turbidity units，NTU）与底栖辐照度（光合有效辐射 photosynthetically active radiation，PAR，400-700 nm），每次测量包含10秒内整合的20个数据点。

每次采样时，在每个地点内的2个站点采集表层水样，测定叶绿素a（chlorophyll a）、脱镁叶绿素（phaeophytin）、颗粒态氮（particulate nitrogen，PN）、颗粒态磷（particulate phosphorus，PP）、颗粒态有机碳（particulate organic carbon，POC）、溶解态无机氮（dissolved inorganic nitrogen，DIN）、溶解态无机磷（dissolved inorganic phosphorus，DIP）、溶解态有机营养盐（dissolved organic nutrients，DON和DOP）及总悬浮物（total suspended solids，TSS）。以站点及采样事件为重复，计算每个季节的水质指数（water quality index，WQI），该指数由水柱营养盐变量的z分数转换值之和得出。

每次采样时，从6个鹿角杯形珊瑚（Pocillopora damicornis）群体中心采集约6厘米长的顶端分支，分析的生理参数包括共生体密度（8次重复计数）、叶绿素a含量及骨骼密度（以干重与浮力重量的比值计算）。

海表温度（sea surface temperature，SST）、表面辐照度（单位：μmol photons m⁻² s⁻¹）及风速（单位：m s⁻¹）数据每半小时记录一次，来源于澳大利亚海洋科学研究所在克利夫兰湾（Cleveland Bay）和戴维斯礁运营的自动气象站（automatic weather stations，AWS）。基于这些气象数据，计算每次采样前14天的平均SST、平均每日总表面辐照度（单位：μmol photons m⁻² day⁻¹）及平均风速；克利夫兰湾的平均风速用于指示波高影响，进而反映沉积物再悬浮情况。汤斯维尔地区2005年5月至2007年5月的月总降雨量数据来自气象局（Bureau of Meteorology）。

本研究旨在量化环境参数的时间变化，建立浊度的潜在胁迫阈值，并验证环境条件变化可通过珊瑚生物指标响应来衡量这一假设；同时探究生物指标与环境参数之间关系的显著性，评估其对水质变化的特异性。

本研究项目由流域到礁合作研究中心（Catchment to Reef Cooperative Research Centre，系大堡礁世界遗产区合作研究中心“CRC Reef”及雨林合作研究中心（Rainforest CRC）的补充项目）与澳大利亚海洋科学研究所联合资助。

感谢Glenn De’ath协助统计分析，Michelle Skuza和Margaret Wright处理营养盐及叶绿素样本；感谢Jon Brodie及匿名审稿人提出的建设性意见，助力手稿完善；感谢昆士兰州自然资源与水务部（Department of Natural Resources and Water, Queensland）的Ken Rohde提供卫星图像。