Bleaching of coral communities on nearshore reefs of the central Great Barrier Reef after Cyclone Sadie (1994)

The nearshore reefs, Brook Islands Reef (2 sites), Iris Point Reef at Orpheus Island (1 site) and Pandora Reef (4 sites) were surveyed using swim survey and video techniques in February 1994. The Pandora Reef sites were resurveyed in April 1994. Meandering SCUBA and/or snorkel swims were used to record an inventory of the coral species at each site and to estimate the severity of coral bleaching. Swims of approximately 100 m were conducted at depths of between 0 to 3 m, 4 to 7 m and 8 to 12 m below approximate mean low water (mlw) level. For each species, the relative abundances of unaffected, partially bleached and totally bleached colonies were estimated to the nearest 20%. At Iris Point Reef and Pandora Reef, the coral communities were also filmed using a Sony Hi-8 Video camera from about 50 cm above the substrate during the swims, producing video profiles covering about 30-50 cm width of reef substrate. The videos were inspected for additional species not previously recorded during the swims. The perimeter of bleached tissue was filmed on four partially-bleached massive corals and marked with stainless steel nails. At Pandora Reef, video belt-transects of 50 m length were filmed at three depths (1 to 3 m, 4 to 6 m and 9 to 11 m below approximate mlw level) at four sites around the reef perimeter. The sites were selected haphazardly within areas known to support the range of major coral community types present. Transects were marked with a glass fibre metric tape measure laid along the depth contours. The starting point of each transect was marked with a buoy. The transects were filmed from approximately 50 cm above the substratum, providing a video band-width of 30 to 50 cm. Each transect took about 4 minutes to film. The transects in the second survey (April 1994) were located near the buoyed positions, in the same depth ranges and community types, but did not follow the precise path of the original transects.
The nearshore reefs (Brook Islands Reef, Iris Point Reef at Orpheus Island and Pandora Reef), were surveyed to determine the extent and severity of bleaching due to the influence of a coalesced flood plume associated with Cyclone Sadie. Pandora Reef was resurveyed eight weeks after exposure to the plume to assess whether recovery from the bleaching event had occurred.
Tropical cyclone Sadie degenerated into an intense rain depression over the North Queensland coast on the 31st January 1994. A flood plume from the Herbert River and adjacent streams extended approximately 20 km offshore on the 2nd February 1994. Several nearshore reefs were covered by the plume, including Pandora Reef, and reefs fringing the Brook and Palm Island groups. Further heavy rain occurred some two weeks following the cyclone, particularly in the Ingham area causing a second flood of smaller magnitude than that associated with cyclone Sadie.

1994年2月，采用游泳式调查法（swim survey）与视频技术，对三处近岸礁体开展调查：布鲁克群岛礁（2个样点）、奥费斯岛鸢尾角礁（1个样点）以及潘多拉礁（4个样点）。其中潘多拉礁的样点于1994年4月完成复勘。
本次调查采用蜿蜒式水肺潜水（SCUBA）与/或浮潜（snorkel）巡查路线，记录各调查点的珊瑚物种名录，并量化珊瑚白化的严重程度。每条巡查路线长度约100米，设置在近似平均低潮位（mlw）以下的0~3米、4~7米及8~12米三个水深区间内。
针对每一种珊瑚，研究人员将未受影响、部分白化及完全白化的珊瑚群体的相对丰度估算至最接近的20%档位。在鸢尾角礁与潘多拉礁的巡查过程中，调查人员同时在距离礁体底质约50厘米的高度，使用索尼Hi-8摄像机（Sony Hi-8 Video camera）进行拍摄，获取覆盖礁体底质宽度约30~50厘米的视频剖面。后续对这些视频进行检视，以补充记录游泳式调查法中未被发现的珊瑚物种。
此外，研究人员对4株部分白化的块状珊瑚的白化组织边缘进行拍摄，并使用不锈钢钉（stainless steel nails）进行点位标记。
针对潘多拉礁，调查人员在礁体周边的4个样点，分别在三个水深区间（近似平均低潮位以下1~3米、4~6米及9~11米）开展长度为50米的视频样带（video belt-transects）调查。样点在已知涵盖该礁体主要珊瑚群落类型的区域内随机选取。调查样带采用沿等深线铺设的玻璃纤维卷尺（glass fibre metric tape measure）进行标记，每个样带的起始点均设置浮标定位。拍摄时摄像机距底质约50厘米，获取宽度为30~50厘米的视频带，每条样带的拍摄时长约为4分钟。
1994年4月开展的第二次复勘中，样带的布设位置紧邻第一次调查的浮标点位，水深区间与覆盖的珊瑚群落类型均保持一致，但未严格沿用上一次调查的样带路径。
本次对近岸礁体（布鲁克群岛礁、奥费斯岛鸢尾角礁与潘多拉礁）的调查，旨在明确与热带气旋萨迪（Cyclone Sadie）相关的合并性洪水羽流所引发的珊瑚白化范围与严重程度。潘多拉礁在暴露于该洪水羽流8周后被复勘，以评估该白化事件后的珊瑚恢复情况。
1994年1月31日，热带气旋萨迪在澳大利亚昆士兰州北部海岸消散为强降雨低压系统。1994年2月2日，赫伯特河（Herbert River）与邻近溪流形成的洪水羽流向海外延伸约20公里，覆盖了包括潘多拉礁以及布鲁克群岛、棕榈群岛周边礁体在内的多处近岸礁体。气旋过境约两周后，当地再次出现强降雨，尤以因哈姆（Ingham）地区最为严重，引发了规模小于热带气旋萨迪相关洪水的第二次小型洪水。