Changes in coral reef communities along a gradient of river discharge, Pohnpei, Micronesia

Change to coral communities along a gradient of increasing exposure to a mud-discharging river in the Enipein Catchment, Pohnpei, Micronesia were quantified by the two principal authors (PICRC) using video transects at 5 sites, each with 3 replicate stations. Site 1 was closest to the river mouth and Site 5 farthest away (just under 2 km).For each of 75 20 m transects, 200 sample points were generated by stopping the video every 2-3 s and identifying benthos under 5 fixed sample points on the screen (40 frames per transect). Cover was estimated for the benthos categories: abiotic substrata were recorded as carbonate (consolidated, including crustose coralline algae), mud (only used so thick no other substratum was visible), sand or rubble. Hard corals (scleractinia) were identified to the genus level where possible; corals in the Faviidae and Fungiidae were recorded to the family level; the three most abundant Porites taxa were recorded separately (massive Porites, Porites cylindrica, and Porites rus); unidentfied corals were grouped together - 24 species were identified. Other benthic groups recorded were: the calcareous green alga Halimeda, other macroalgae, soft corals, the calcareous hydrozoan Millepora, and sponges. To analyse in detail how, and at what scale, coral reef communities are affected by changes along a water quality gradient moving away from the mouth of a river in a small island setting.To contribute to understanding of coral reef communities and potential changes in response to increased terrestrial runoff. Corals identified: Acropora spp., Astreopora, Echinopora, Faviidae, Fungiidae, Galaxea, Goniopora, Hydnophora, massive Porites, Millepora, Montipora, Oxypora, Pachyseris spp., Pavona spp., Pectinia, Plerogyra, Pocillopora, Porites spp., Porites cylindrica, Porites foliose, Porites rus, Seriatopora, Stylophora, Symphyllia, Turbinaria spp.Lobophyllia, Echinophyllia

针对密克罗尼西亚波纳佩岛埃尼皮恩流域（Enipein Catchment）内沿排泥河流暴露梯度（暴露程度随距河口距离缩短而升高）的珊瑚群落变化，由两位核心作者依托PICRC开展量化研究：共设置5个采样点，每个采样点布设3个重复站位，采用视频样带法完成调查。其中采样点1距河口最近，采样点5距河口最远，直线距离不足2公里。针对全部75条20米长的视频样带，通过每2-3秒暂停视频并识别屏幕上5个固定采样点下方的底栖生物（每条样带对应40帧画面），共生成200个采样点。研究人员对以下底栖类别的覆盖度进行了估算：非生物基质分为三类，碳酸盐基质（固结型，包含壳状珊瑚藻）、泥质基质（仅当泥层过厚以致无法辨识其他基质时归类于此）、沙质基质或碎石基质。硬珊瑚（石珊瑚目Scleractinia）尽可能鉴定至属级水平；蜂巢珊瑚科（Faviidae）与石芝珊瑚科（Fungiidae）的珊瑚仅鉴定至科级水平；三种优势多孔珊瑚类群单独记录：团块型多孔珊瑚（massive Porites）、圆柱多孔珊瑚（Porites cylindrica）以及尖孔珊瑚（Porites rus）；未鉴定珊瑚统一归为一类，本次研究共鉴定出24种珊瑚。本次记录的其他底栖生物类群包括：钙质性绿藻仙掌藻属（Halimeda）、其他大型藻类、软珊瑚、钙质性水螅虫千手珊瑚属（Millepora）以及海绵。本研究旨在详细解析：在小型岛屿环境中，沿远离河口的水质梯度变化，珊瑚礁群落所受影响的方式与尺度，以期为理解珊瑚礁群落结构及其对陆地径流增加的潜在响应提供研究支撑。本次鉴定的珊瑚类群包括：轴孔珊瑚属（Acropora spp.）、星孔珊瑚属（Astreopora）、棘孔珊瑚属（Echinopora）、蜂巢珊瑚科（Faviidae）、石芝珊瑚科（Fungiidae）、盔形珊瑚属（Galaxea）、角孔珊瑚属（Goniopora）、合叶珊瑚属（Hydnophora）、团块型多孔珊瑚（massive Porites）、千手珊瑚属（Millepora）、表孔珊瑚属（Montipora）、尖叶珊瑚属（Oxypora）、厚丝珊瑚属（Pachyseris spp.）、牡丹珊瑚属（Pavona spp.）、梳状珊瑚属（Pectinia）、翼杯珊瑚属（Plerogyra）、杯形珊瑚属（Pocillopora）、多孔珊瑚属（Porites spp.）、圆柱多孔珊瑚（Porites cylindrica）、叶状多孔珊瑚（Porites foliose）、尖孔珊瑚（Porites rus）、枝孔珊瑚属（Seriatopora）、指形珊瑚属（Stylophora）、叶状珊瑚属（Symphyllia）、陀螺珊瑚属（Turbinaria spp.）、叶状珊瑚属（Lobophyllia）、棘叶珊瑚属（Echinophyllia）