Baseline coral and benthic cover surveys of Keppel Islands reefs, Great Barrier Reef: 2008-2010

A total of 20 survey sites were chosen using a combination of high resolution aerial photographs and local knowledge, to ensure that all significant reef systems in the central Keppel Island group were represented. Aerial photos were geo-rectified in Google EarthTM and reef area estimated by tracing the outline of the reef which was clearly visible in the photos. The sites chosen were located on the fringing reefs surrounding Bald Rocks, Barren Island and Child Island, Clam Bay, Egg Rock, Halftide Rocks, Halfway Island, Humpy Island, Leeke's Beach, Man and Wife Rocks, Miall Island, Middle Island, Monkey Point, Shelving Point, North Keppel Island, Outer Rocks, Parker's Bommie (Big Peninsula), Passage Rocks, Pelican Island, Pumpkin Island and Wreck Bay. Surveys were conducted between April 2008 and December 2009. Coral species and their abundance (ranked % abundance) were assessed during a random swim over ~60 minutes at each of the 20 sites. Species lists were limited to scleractinian corals. Most coral species could be adequately identified in the field with the exception of those in the Poritidae (massive growth form) and Fungiidae genera, which were counted as one species if these were present. Digital still photographs of the features of each species were taken to verify identity. Each species was ranked in terms of abundance and compared to the total live hard coral cover using a scale of 0-5 (0 = none present; 1 = 1-10%; 2 = 11-30%; 3 = 31-50%; 4 = 51-75%).The cover of benthic communities was assessed at each site (except for Leeke's Beach and Clam Bay) along two haphazard 50 m transects on the reef flat (0-2.0 m at chart datum, 2.4-4.8 m at mean sea level) and reef slope (6.0-12.0 m at chart datum, 8.4-14.4 m at mean sea level). Transects were photographed every 2 m at a height of 1 m above the substratum using a digital still camera (4 Mp) fitted with a 16 mm wide angle lens. To enable calculation of the average gradient between the reef flats and slopes, geo-referenced images were obtained for each transect using a towed GPS set to record a track at 5 second intervals, which was later matched to the images using the software RoboGeoTM. Digital still images were analysed using 20 random points per image with the program CPCeTM v3.1. Cover was assessed as the percentage of the total biotic and abiotic benthos averaged across the replicate transects on reef flats and slopes. Benthic cover was classified into the proportion of macro-algae, abiotic, coralline algae, turf algae, hard live coral and soft coral.To assess the variation in light levels across sites, predominantly due to variation in turbidity, the light attenuation coefficient (Kd) was derived from photosynthetically active radiation (PAR) loggers (Odyssey, Dataflow Systems, NZ) deployed at each site (except Leeke's Beach) at a depth of 5-7 m. Light was recorded every 10 minutes for periods of 1-12 weeks. Sea temperature was recorded at half-hourly intervals using Odyssey temperature loggers (Dataflow Systems Pty Ltd, NZ) deployed at each site (except Leeke's Beach) on the reef slope (5-7 m at LAT). Habitat profiles were estimated by measuring the gradient (slope) between the start of reef flat and slope transects for each site from the geo-rectified images using Google EarthTM. The depth at the reef flat was subtracted from the depth at the reef slope and then divided by the distance between the points.To assess the influence of current flow on the species assemblage at each site, current strengths were catagorized based on local knowledge as: 1 = strong tidal combined with longshore currents; 2 = medium current (mainly tidal) but some longshore current influence; 3 = mostly diurnal tidal currents which are protected from strong longshore currents and ocean swell.To assess the influence of 3-D habitat complexity (rugosity) on the coral species assemblages at the 20 sites, each site was subjectively categorized as: 1 = high rugosity as a result of bommies and rocks creating high 3-D habitat structure and a range of habitat types; 2 = average rugosity with reef flats and slopes exhibiting range of coral growth morphologies and scattered bommies; and 3 = low rugosity (reef flats and slopes with extensive mono-specific stands dominated mainly by Acropora spp.).The aim of this study was to conduct a detailed assessment of coral biodiversity and abundance as well as a number of key physical parameters (temperature, light, habitat profile, reef rugosity and current strength) on an inshore reef system to elucidate patterns, linkages and implications for conservation. The Keppel Islands region in the southern Great Barrier Reef was chosen for the study because it is a relatively small and isolated inshore fringing reef system that has a history of frequent disturbance and strong regeneration between events.

本研究结合高分辨率航空影像与本地调研资料，共遴选20个调查点位，以确保凯珀尔群岛（Keppel Island Group）中部所有重要礁体系统均被覆盖。研究人员在谷歌地球（Google Earth™）中对航空影像进行地理校正，并通过描摹影像中清晰可见的礁体轮廓估算礁体面积。所选点位分布于秃礁（Bald Rocks）、荒岛（Barren Island）、蔡尔德岛（Child Island）、蛤蜊湾（Clam Bay）、蛋礁（Egg Rock）、半潮礁（Halftide Rocks）、中途岛（Halfway Island）、汉皮岛（Humpy Island）、利克海滩（Leeke's Beach）、夫妻礁（Man and Wife Rocks）、迈尔岛（Miall Island）、中岛（Middle Island）、猴角（Monkey Point）、搁架角（Shelving Point）、北凯珀尔岛（North Keppel Island）、外礁（Outer Rocks）、帕克岩隆（大半岛）（Parker's Bommie (Big Peninsula)）、航道礁（Passage Rocks）、鹈鹕岛（Pelican Island）、南瓜岛（Pumpkin Island）与沉船湾（Wreck Bay）周边的裙礁。

调查工作于2008年4月至2009年12月间开展。针对20个点位，研究人员通过单次约60分钟的随机游泳调查，评估珊瑚物种及其丰度（以百分比丰度排序）。调查物种仅限定为石珊瑚（scleractinian corals）。多数珊瑚物种可在野外直接准确鉴定，但孔珊瑚科（Poritidae，呈团块状生长型）与蕈珊瑚科（Fungiidae）物种除外，若该类群存在则统一计为一个物种。研究人员拍摄各物种特征的数码静态照片，以辅助验证物种鉴定结果。研究人员基于丰度对各物种进行排序，并以0-5级量表与总活硬珊瑚覆盖率进行对比（0：无该物种分布；1：1%-10%；2：11%-30%；3：31%-50%；4：51%-75%）。

除利克海滩（Leeke's Beach）与蛤蜊湾（Clam Bay）外，研究人员在其余点位的礁坪（海图基准面下0-2.0米，平均海平面下2.4-4.8米）与礁坡（海图基准面下6.0-12.0米，平均海平面下8.4-14.4米）上，沿两条随机设置的50米样带开展底栖群落覆盖率调查。研究人员使用搭载16毫米广角镜头的400万像素数码静态相机，在距底质1米高度处，每隔2米对样带进行拍摄。为计算礁坪与礁坡间的平均坡度，研究人员使用拖曳式GPS（设置为每5秒记录一次轨迹）获取每条样带的地理参考影像，后续通过RoboGeo™软件将轨迹与影像进行匹配。研究人员使用CPCe™ v3.1软件，对每张影像选取20个随机点进行分析。底栖覆盖率以生物与非生物底质的总占比百分比计算，并对礁坪与礁坡的重复样带结果取平均值。底栖覆盖率被划分为大型藻类、非生物底质、珊瑚藻、藻席藻类、活硬珊瑚与软珊瑚六大类。

为评估各点位光照水平的差异（主要由浊度变化导致），研究人员在除利克海滩外的所有点位的5-7米水深处，部署光合有效辐射（PAR）记录仪（Odyssey, Dataflow Systems, 新西兰）以获取光衰减系数（Kd）。光照数据每10分钟记录一次，记录周期为1至12周。研究人员在除利克海滩外的所有点位的礁坡（5-7米，最低天文潮位LAT）部署Odyssey温度记录仪（Dataflow Systems Pty Ltd, 新西兰），以每半小时一次的频率记录海水温度。

研究人员通过谷歌地球（Google Earth™）的地理校正影像，测量各点位礁坪样带起始点与礁坡样带起始点间的坡度，以估算生境剖面特征。具体计算方式为：用礁坡水深减去礁坪水深，再除以两点间的水平距离。为评估水流对各点位物种组合的影响，研究人员基于本地调研资料将水流强度划分为三类：1级：强潮流与沿岸流共同作用；2级：中等强度水流（以潮流为主，但受一定沿岸流影响）；3级：以全日潮流为主，且处于遮蔽环境，免受强沿岸流与海浪冲击。

为评估三维生境复杂度（生境粗糙度）对20个点位珊瑚物种组合的影响，研究人员对各点位进行主观分类：1级：生境粗糙度高，岩隆与礁石形成复杂的三维生境结构与多样的生境类型；2级：生境粗糙度中等，礁坪与礁坡发育多种珊瑚生长形态，且散布少量岩隆；3级：生境粗糙度低，礁坪与礁坡以单优群落为主，且主要由轴孔珊瑚属（Acropora spp.）物种构成。

本研究旨在对近岸礁体系统的珊瑚生物多样性与丰度，以及温度、光照、生境剖面、礁体粗糙度与水流强度等关键物理参数开展详细评估，以阐明其分布模式、关联机制及其对保护工作的启示。本研究选取大堡礁（Great Barrier Reef）南部的凯珀尔群岛海域作为研究区域，因其属于规模较小且相对孤立的近岸裙礁系统，历史上频繁受到扰动，且扰动间具备较强的再生能力。