Bleaching in larger benthic foraminifera from the Great Barrier Reef

Experiments were conducted to determine whether larger benthic foraminifera is prone to bleaching caused by increases in temperature and nutrient levels. The experiments aimed to characterise the physiological stress threatening these species, predicted to occur on tropical reef waters in the near future. Nutrient levels were chosen to represent naturally occurring nutrient concentrations during flood-plume events on the GBR, and temperatures were chosen to reflect current and future predictions for the GBR (Lough et al. 2006; Lough 2007).

Specimens of Amphistegina radiata and Heterostegina depressa were collected during dry season 2009 and wet season 2010, from the Whitsundays area nearby sites Double Cone Island, Border Island, Deloraine Island and Edward Island. Calcarina hispida specimens were collected from Heron Island 2009 and Calcarina mayorii from Magnetic Island. Daily average SST was obtained from AIMS AWS stations at Hardy Reef and Heron Island, temperature logger are Nelly Bay. Additional samplesof A. radiata and H. depressa were collected from Dent Island and Bait Reef.

A 6 day experiment with temperature manipulation were carried out with five individually set temperatures 23, 28, 30 32 and 33, exposing samples of A.radiata, H. depressa, and C. hispida. These experiments were repeated three times for A. radiata and H. depressa. To avoid thermal shock, the specimens were gradually introduced to the five different temperature treatments. Subsequent experiments used light levels of 11 -15 µmol photos m-2 s-1.

A 30-day flow-through experiment was conducted where the effects of three temperature ranges and three nutrient levels were studied simultaneously: Temperature: 26, 29 and 31, and nutrient concentrations of 0.5, 1.0 and 1.4 µmol L-1. Specimens of A.radiata and H.depressa contained in six-well plates, and C. mayorii was contained in polypropylene tubes.

Analysis included photosynthetic efficiency, Chl a, motility and growth measurements in A. raditata. Results of these experiments suggested that physiological stress and bleaching are species specific.

This research was supported by the Australian government’s Marine and Tropical Sciences Research Facility, implemented by the Reef and Rainforest Research Centre in northern Queensland, Australia.

本实验旨在探究大型底栖有孔虫（larger benthic foraminifera）是否易因温度与营养盐水平升高引发白化现象。实验目标为明确威胁此类物种的生理胁迫机制，而该类胁迫预计将在不久的将来出现在热带礁区海域。本次实验选取的营养盐水平，对应大堡礁（Great Barrier Reef, GBR）洪水径流事件期间的自然营养盐浓度；温度设置则参考了大堡礁当前及未来的气候预测（Lough等，2006；Lough，2007）。

2009年旱季与2010年雨季期间，研究者从惠森迪地区的锥岛（Double Cone Island）、边境岛（Border Island）、德洛莱恩岛（Deloraine Island）及爱德华岛（Edward Island）附近海域采集了辐射双盖虫（Amphistegina radiata）与凹陷异盖虫（Heterostegina depressa）的样本。粗糙钙房虫（Calcarina hispida）样本于2009年采自赫伦岛（Heron Island），梅氏钙房虫（Calcarina mayorii）样本采自磁岛（Magnetic Island）。日平均海表温度（Sea Surface Temperature, SST）数据取自哈迪礁与赫伦岛的AIMS（澳大利亚海洋科学研究所，Australian Institute of Marine Science）自动气象站，温度记录仪部署于内利湾（Nelly Bay）。另有辐射双盖虫与凹陷异盖虫的额外样本采集于登特岛（Dent Island）与诱饵礁（Bait Reef）。

开展了为期6天的温度调控实验，设置23、28、30、32及33℃共5个独立温度梯度，对辐射双盖虫、凹陷异盖虫及粗糙钙房虫的样本进行处理。其中辐射双盖虫与凹陷异盖虫的实验重复3次。为避免热冲击，实验对象被逐步适应至5个不同的温度处理条件。后续实验采用的光照强度为11~15 μmol photons m⁻² s⁻¹。

另有一项为期30天的流水实验，同步探究3个温度梯度与3个营养盐浓度水平的交互效应：温度设置为26、29及31℃，营养盐浓度分别为0.5、1.0与1.4 μmol L⁻¹。实验中，辐射双盖虫与凹陷异盖虫的样本饲养于六孔板内，梅氏钙房虫的样本则置于聚丙烯管中。

针对辐射双盖虫的分析指标包括光合效率、叶绿素a（Chlorophyll a, Chl a）含量、运动能力及生长速率。实验结果表明，生理胁迫与白化现象具有物种特异性。

本研究得到澳大利亚政府海洋与热带科学研究基金资助，项目由澳大利亚昆士兰州北部的珊瑚礁与雨林研究中心执行。