Investigation of light as a limiting factor in the distribution of benthic symbiont bearing foraminifera on the Great Barrier Reef (MTSRF Project 3.7.1)

During August 2005, sediment was collected from four reefs in the Whitsunday Islands and two adjacent midshelf reefs, situated along a previously studied water quality gradient. The reefs at Repulse and Lindeman Islands are influenced by discharge generated by the Proserpine and O'Connell Rivers. In the outer Whitsunday Islands, Hook and Edward Islands reefs, are subject to terrestrial influence, which is largely derived from the islands themselves. The midshelf reefs, Barb Reef and Reef 19-138 are essentially unaffected by terrestrial discharge. Two sites were randomly chosen on the less exposed leeward side of each reef. At each site samples were collected from three depth zones along the reef slope: 2 to 5 m, 6 to 8 m and 9 to 13 m. For each depth zone at each site, three core samples were collected using cut-off 60 ml syringes. Each syringe was pressed vertically into the sand for at least half its length and all but the top 1cm of each core was discarded. Samples were combined to form a single sample per depth station and preserved in ethanol. Samples were later rinsed, dried and subsamples of symbiont bearing foraminifera identified. Amphistegina spp., Calcarina spp. and Heterostegina depressa, collected from the sediment sampling sites at Edward Island were cultured in tubes within a series of tanks in an outdoor aquarium system set up in mid September 2005 at AIMS. Specimens were subjected to three light regimes: open to sunlight, 30% sunlight and 10% sunlight.Over a two week period in November/December 2005, light measurements, temperature and salinity were recorded in each tank. Images of each individual foraminifera were taken before and at intervals during the experiment and the surface area of each individual determined. Pulse-amplitude-modulated (PAM) fluorometry was applied to assess the health of the symbiotic diatoms and their adaptation to various light levels. Additional specimens of the three taxa were collected from the Whitsunday Islands and the same process was applied within 2 hours of collection.
Field and experimental studies were undertaken to investigate the importance of light as an environmental factor influencing physiology and distribution of tropical benthic foraminifera.

2005年8月，研究人员沿此前已被探明的水质梯度带，在惠森迪群岛（Whitsunday Islands）的4座珊瑚礁以及邻近的2座陆架中部礁体中采集沉积物样品。雷普瑟岛（Repulse Island）与林德曼岛（Lindeman Island）的礁体受到普罗瑟派恩河（Proserpine River）与奥康奈尔河（O'Connell River）径流的影响。外海惠森迪群岛的胡克岛（Hook Island）与爱德华岛（Edward Island）礁体则受陆地径流影响，其径流主要来自岛体自身。陆架中部礁体巴伯礁（Barb Reef）与19-138号礁基本不受陆地径流影响。每个珊瑚礁的背风侧（受波浪扰动较弱的一侧）随机选取2个采样点；每个采样点沿礁坡设置3个深度带：2~5 m、6~8 m与9~13 m，采集沉积物样品。针对每个采样点的每个深度带，使用截去前端的60 mL注射器采集3份柱状沉积物样品：将注射器垂直插入沙层至至少一半长度，随后弃去除顶部1 cm以外的全部柱样。将同深度采样点的三份柱样混合为一份复合样品，以乙醇保存。后续对样品进行冲洗、干燥，并筛选出携带共生体的有孔虫（foraminifera）亚样品。从爱德华岛沉积物采样点采集的双盖虫属（Amphistegina spp.）、钙扇虫属（Calcarina spp.）与凹陷异盖虫（Heterostegina depressa）样本，于2005年9月中旬在澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）搭建的室外水族系统中，置于多组水箱的培养管内进行养殖。实验对象分别接受三种光照处理：全光照、30%自然光与10%自然光。2005年11-12月的两周内，研究人员记录了各水箱的光照强度、水温与盐度。实验开始前及实验期间定期拍摄每只有孔虫的图像，并测定其个体表面积。采用脉冲振幅调制荧光法（Pulse-amplitude-modulated fluorometry, PAM），评估其共生硅藻的健康状态及对不同光照水平的适应性。从惠森迪群岛额外采集该三类群的标本，于采集后2小时内开展相同实验流程。
本研究通过野外调查与室内实验，探讨光照作为环境因子对热带底栖有孔虫生理特征与分布格局的调控作用。