Scleractinian Coral Fauna of Easter Island (Rapa Nui)

Three surveys at Easter Island (Rapa Nui) spanning the period 1999–2005, and examination of private and museum collections, have revealed a depauperate zooxanthellate scleractinian fauna. Collections were all made off island shelf exposures, from tide pools to 70 m with scuba, and by dredging to 100 m. With synonymies, reassignments, and two new records in the families Pocilloporidae and Faviidae, the Easter Island coral fauna now comprises 13 species. Pocilloporid and poritid coral abundances were generally high on all island shelves protected from southern swells. A cluster analysis of the coral fauna relationships of 19 south, central, and far-eastern Pacific sites indicates a strong affinity between those of Easter Island and the far-eastern Pacific equatorial region (e.g., Colombia, Ecuador, Panama´, and the Galapagos Islands). The precipitous drop in coral species richness from the Pitcairn Island group (61 species) to Easter Island suggests the presence of a dispersal barrier between these two remote southeastern Pacific areas, separated by @ 1,800 km of deep ocean waters. Consideration of the surface circulation based on satellite-tracked surface drifters confirms this conclusion. Surface currents are from east to west along the topography on which Easter and Sala-y-Gomez Islands sit, suggesting a substantial barrier to recruitment from the west.1999年至2005年间在复活节岛（Easter Island，拉帕努伊Rapa Nui）开展的三次调查，以及对私人收藏与博物馆馆藏标本的检视，揭示了该区域与虫黄藻共生的石珊瑚（zooxanthellate scleractinian）类群的物种贫乏现象。所有采集标本均取自岛陆架暴露区域，通过水肺潜水覆盖潮间带至70米水深范围，拖网采样则可抵达100米水深。经过同物异名修订、类群重新归类，并在杯形珊瑚科（Pocilloporidae）和蜂巢珊瑚科（Faviidae）中新增两个区域新记录种后，复活节岛的珊瑚类群目前共计13种。在所有免受南部涌浪影响的岛陆架区域，杯形珊瑚科与微孔珊瑚科（Poritidae）的珊瑚丰度普遍较高。对19个南太平洋、中太平洋以及东太平洋远域采样点的珊瑚类群亲缘关系进行聚类分析后发现，复活节岛的珊瑚类群与东太平洋赤道区域（如哥伦比亚、厄瓜多尔、巴拿马以及加拉帕戈斯群岛）的类群具有极强的亲缘相似性。从皮特凯恩群岛群（共61种珊瑚）到复活节岛，珊瑚物种丰富度出现骤降，这表明这两个偏远的东南太平洋区域之间存在扩散障碍，二者被约1800公里的深海水域分隔。基于卫星追踪表层浮标得到的表层环流分析验证了这一结论：复活节岛与萨拉戈麦斯群岛（Sala-y-Gomez Islands）所处的地形沿线，表层洋流自东向西流动，这意味着来自西侧的珊瑚幼体补充存在显著障碍。