Effects of turbid runoff on the coral communities of Gebe and Gag Islands, Eastern Indonesia

Surveys of the reefs around Gebe and Gag Islands were undertaken from 27th January to 7th February 1997, using SCUBA. Sites selected for surveys coincided as much as practicable with monitoring sites previously selected for placement of sediment tubes. Fifteen sites were surveyed on Gebe Island and 11 sites were surveyed on Gag Island. The position of each site was recorded using a portable GPS unit.Each survey took between 30 and 60 minutes to complete and covered distances of between 100m and 300m. The sites were not equivalent in size, rather they varied in respect to the amount of reef or coral community present and time available at a given location. Each site was classified in terms of the amount of reef development observed. To determine coral community composition, taxa were identified in situ to genus and species for most hard corals, genus for most soft corals and macro-algae and to higher taxonomic rank for sponges, zoanthids and other macro-benthos. It was impossible to differentiate all species of hard coral underwater and accurate identifications of certain taxa to species required genetic methods beyond the scope of this survey. Thus some hard corals were grouped at the level of genus and colony morphology (e.g. Porites spp. of massive growth-form). At the end of each survey, each taxon was ranked subjectively in terms of its relative abundance in the area surveyed. The abundance ranks do not relate directly to benthic cover, rather they represent the relative numbers of taxa in the sites. For each species, its size frequency distribution was estimated as the relative proportion of colonies in each of 3 size categories.Sites were described using visual estimates of the approximate percentage cover occupied by the major benthic attributes, of the overall substrate at each site. Field notes were recorded on the presence of any unique or outstanding biological features, such as particularly large corals or unusual community compositions. Each site was also classified in terms of the amount of reef development observed. At each site, a video 'profile' was filmed across the reef zonation from the base of the reef slope to the inner reef flat, using a SONY Hi-8 video camera in a waterproof housing. Profiles were filmed perpendicular to the reef surface, from a distance of approximately 40cm, giving a video record of the reef of width of approximately 40cm. The resulting profiles are stored at AIMS as a permanent visual record of the reef communities. To examine the extent of mine influence, the profiles of sites in the vicinity of the Gebe Island mine were analysed for percent cover of the major benthic attributes (including silt) using a SONY Hi-8 video editor. The elapsed time of each profile was determined and the tape was stopped regularly at 4 second intervals along the profile. At each stop, the benthic attribute located under each of 5 fixed points (one near each corner; one in the center of the video monitor) was identified and recorded into a computer spreadsheet, as one of 9 benthic categories. The resultant data were expressed as five point running means of percent cover of the major benthos along the profile from the base of the reef slope to the inner reef flat.
The objectives of this survey were:1) to reconnoitre the coral reefs around Gag Island and Gebe Island (both disturbed and undisturbed), provide a brief description of community structure and provide an opinion as to whether the reefs are comparable for impact assessment purposes.2) to examine a series of reef sites around Gebe Island at various distances from the active mine site and assess and rate the severity of damage at each location.3) to compare the ratings of observed damage with other sites that have been disturbed by high sedimentation and/or turbidity.4) To comment on the potential for settlement, recruitment and recovery of damaged reefs after cessation of mining.
Large deposits of nickel and other minerals have been discovered on the eastern Indonesian islands of Gebe (northern Maluku Province) and Gag (Irian Jaya Province). PT Aneka Tambang has mined the deposit on Gebe Island since 1979, with infrastructure development occurring since the late 1960s. The nickel deposit on Gag Island has not been mined to date, but a mining camp has been established and exploratory studies are currently underway. Experience at Gebe Island suggests that total control of highly coloured and turbid runoff will be very difficult to achieve at Gag Island (especially due to its more mountainous terrain).

本研究于1997年1月27日至2月7日采用水肺潜水（SCUBA）技术，对印度尼西亚格贝岛（Gebe）与加格岛（Gag）周边的珊瑚礁开展调查。本次调查选取的点位，尽可能与此前为布设沉积物采样管而选定的监测点位相重合。格贝岛共完成15个点位的调查，加格岛共完成11个点位的调查。各点位的空间位置采用便携式全球定位系统（GPS）记录。
单次调查耗时30至60分钟，覆盖调查距离100至300米。各点位规模并不统一，而是根据现有礁体或珊瑚群落的覆盖范围，以及单点位可分配的调查时长进行调整。依据现场观测到的礁体发育程度对各点位进行分类。
为明确珊瑚群落组成，研究人员在现场对多数硬珊瑚鉴定至属、种水平；多数软珊瑚及大型藻类鉴定至属水平；海绵、群体海葵及其他大型底栖生物则鉴定至更高分类阶元。由于水下无法区分所有硬珊瑚物种，且部分类群的精准物种鉴定需要超出本调查范围的遗传学实验方法，因此部分硬珊瑚按属及群体生长形态进行归类（如块状生长型滨珊瑚属（Porites）物种）。
每次调查结束后，研究人员主观对各分类群的相对丰度进行排序。该丰度排序并不直接对应底栖生物盖度，而是代表调查点位内各分类群的相对数量。针对每一物种，通过将其群落划分为3个尺寸等级，估算其尺寸频率分布，即各尺寸等级的群落占比。
各点位采用目视估算的方式，记录整体底质中主要底栖属性所占的近似百分比盖度。同时记录现场笔记，记录所有独特或显著的生物学特征，如特大型珊瑚或异常的群落组成。此外再次依据观测到的礁体发育程度对各点位进行分类。
在各点位，研究人员采用置于防水外壳中的索尼（SONY）Hi-8摄像机，沿礁体从礁坡基部至内礁坪的礁带方向拍摄视频剖面。拍摄方向垂直于礁体表面，拍摄距离约40厘米，可记录宽度约40厘米的礁体影像。所获剖面影像由AIMS存档，作为礁体群落的永久可视化记录。
为评估矿山活动的影响范围，研究人员对格贝岛矿区周边点位的视频剖面进行分析，采用索尼（SONY）Hi-8视频编辑器统计主要底栖属性（包括沉积物）的百分比盖度。首先确定各剖面的总时长，随后沿剖面以每4秒的间隔暂停录像。在每次暂停时，对视频画面中5个固定点位（画面四角各1个，中心1个）下方的底栖属性进行鉴定，将其归入9个底栖类别之一，并录入计算机电子表格。最终数据以沿礁坡基部至内礁坪剖面的五点移动平均值形式呈现，表征主要大型底栖生物的百分比盖度。

本调查的目标如下：
1. 勘查加格岛与格贝岛周边的珊瑚礁（包括受干扰与未受干扰区域），简要描述其群落结构，并评估这些礁体是否可作为影响评估的可比参照对象。
2. 对格贝岛周边距活跃矿区不同距离的一系列礁体点位进行调查，评估并分级各点位的受损严重程度。
3. 将观测到的受损等级与其他受高沉积作用和/或浊度干扰的点位进行对比分析。
4. 评估矿山停采后受损礁体的定居、补充与恢复潜力。

印度尼西亚东部的格贝岛（北马鲁古省）与加格岛（原伊里安查亚省，现巴布亚省）已探明大型镍矿及其他矿产资源。PT Aneka Tambang自1979年起开采格贝岛的镍矿矿床，相关基础设施建设始于20世纪60年代末。加格岛的镍矿目前尚未商业化开采，但已建立采矿营地，当前正在开展勘探研究。格贝岛的开采经验表明，在加格岛（尤其因其地形更为崎岖）难以完全控制高色度且浑浊的径流排放。