Benthic and substrate cover data derived from photo-transect surveys in Lizard Island Reef conducted on December 10-15, 2011

Underwater georeferenced photo-transect surveys were conducted on December 10-15, 2011 at various sections of the reef at Lizard Island, Great Barrier Reef. For this survey a snorkeler or diver swam over the bottom while taking photos of the benthos at a set height using a standard digital camera and towing a GPS in a surface float which logged the track every five seconds. A standard digital compact camera was placed in an underwater housing and fitted with a 16 mm lens which provided a 1.0 m x 1.0 m footprint, at 0.5 m height above the benthos. Horizontal distance between photos was estimated by three fin kicks of the survey diver/snorkeler, which corresponded to a surface distance of approximately 2.0 - 4.0 m. The GPS was placed in a dry-bag and logged the position as it floated at the surface while being towed by the photographer. A total of 5,735 benthic photos were taken. A floating GPS setup connected to the swimmer/diver by a line enabled recording of coordinates of each benthic photo (Roelfsema 2009).
Approximation of coordinates of each benthic photo was conducted based on the photo timestamp and GPS coordinate time stamp, using GPS Photo Link Software (www.geospatialexperts.com). Coordinates of each photo were interpolated by finding the GPS coordinates that were logged at a set time before and after the photo was captured.
Benthic or substrate cover data was derived from each photo by randomly placing 24 points over each image using the Coral Point Count for Microsoft Excel program (Kohler and Gill, 2006). Each point was then assigned to 1 of 78 cover types, which represented the benthic feature beneath it. Benthic cover composition summary of each photo scores was generated automatically using CPCE program. The resulting benthic cover data of each photo was linked to GPS coordinates, saved as an ArcMap point shapefile, and projected to Universal Transverse Mercator WGS84 Zone 55 South.

2011年12月10日至15日，研究团队于大堡礁（Great Barrier Reef）蜥蜴岛（Lizard Island）的多处礁体区域开展了地理参考水下样带摄影调查（georeferenced photo-transect surveys）。本次调查由浮潜者或潜水员在海底上方行进，使用标准数码相机以固定高度拍摄底栖生境（benthos）照片，并通过水面浮标拖曳一台每5秒记录一次运动轨迹的全球定位系统（Global Positioning System, GPS）。调查所用的标准紧凑型数码相机搭载于水下防水保护壳中，搭配16毫米镜头，可在距底栖生境0.5米的高度处实现1.0米×1.0米的拍摄覆盖范围。相邻照片间的水平距离通过调查潜水员/浮潜者的三次脚蹼划动估算得出，对应水面行进距离约为2.0米至4.0米。该GPS装置被置于防水干燥袋中，随摄影师拖曳的浮标在水面漂浮，同步记录自身位置信息。本次调查共拍摄底栖照片5735张。本次采用的浮标式GPS装置通过绳索与行进者相连，可记录每张底栖照片的拍摄坐标（Roelfsema, 2009）。

研究团队借助GPS照片链接软件（GPS Photo Link Software，官网地址：www.geospatialexperts.com），基于照片拍摄时间戳与GPS位置记录的时间戳，对每张底栖照片的坐标进行近似估算。通过查找照片拍摄前后指定时间点记录的GPS坐标，对每张照片的拍摄坐标进行插值计算。

研究人员借助面向Microsoft Excel的珊瑚点计数程序（Coral Point Count for Microsoft Excel, Kohler & Gill, 2006），在每张照片图像上随机布设24个采样点，以此提取每张照片对应的底栖/基底覆盖数据。随后将每个采样点归类至78种覆盖类型之一，每种类型对应其下方的底栖生境特征。借助CPCE程序可自动生成每张照片的底栖覆盖组成汇总得分。最终将每张照片对应的底栖覆盖数据与GPS坐标进行关联，保存为ArcMap点要素形状文件（ArcMap point shapefile），并投影至WGS84基准下的南纬55度通用横轴墨卡托（Universal Transverse Mercator WGS84 Zone 55 South）投影坐标系。