Abstract A recent boom in hydroelectric development in the world's most diverse tropical river basins is currently threatening aquatic biodiversity on an unprecedented scale. Among the most controversial of these projects is the Belo Monte Hydroelectric Complex (BMHC) on the Xingu River, the Amazon's largest clear-water tributary. The design of the BMHC creates three distinctly altered segments: a flooded section upstream of the main dam, a middle section between the dam and the main powerhouse that will be dewatered, and a downstream section subject to flow alteration from powerhouse discharge. This region of the Xingu is notable for an extensive series of rapids known as the Volta Grande that hosts exceptional levels of endemic aquatic biodiversity; yet, patterns of temporal and spatial variation in community composition within this highly threatened habitat are not well documented. We surveyed fish assemblages within rapids in the three segments impacted by the BMHC prior to hydrologic alteration, and tested for differences in assemblage structure between segments and seasons. Fish species richness varied only slightly between segments, but there were significant differences in assemblage structure between segments and seasons. Most of the species thought to be highly dependent on rapids habitat, including several species listed as threatened in Brazil, were either restricted to or much more abundant within the upstream and middle segments. Our analysis identified the middle section of the Volta Grande as critically important for the conservation of this diverse, endemic fish fauna. Additional research is urgently needed to determine dam operations that may optimize energy production with an environmental flow regime that conserves the river's unique habitat and biodiversity.

中文翻译：

---

新谷河急流鱼类多样性与群落结构：大规模水电开发对保护的启示

摘要 最近在世界上最多样化的热带河流流域水电开发的蓬勃发展目前正以前所未有的规模威胁着水生生物多样性。这些项目中最具争议的是位于亚马逊最大的清水支流新古河上的贝洛蒙特水电站 (BMHC)。BMHC 的设计产生了三个明显改变的部分：主坝上游的淹没部分、大坝和将要脱水的主发电站之间的中间部分，以及因发电站排放而受到流量改变的下游部分。新谷的这一地区以一系列广泛的急流而闻名，被称为大伏特 (Volta Grande)，拥有异常丰富的地方性水生生物多样性。然而，在这个高度受威胁的栖息地内，群落组成的时空变化模式没有得到很好的记录。我们在水文改变之前调查了受 BMHC 影响的三个段中急流内的鱼类组合，并测试了段和季节之间组合结构的差异。鱼类物种丰富度在段间变化不大，但在段间和季节间的组合结构存在显着差异。大多数被认为高度依赖急流栖息地的物种，包括在巴西被列为受威胁的几种物种，要么仅限于上游和中部，要么数量更多。我们的分析表明，Volta Grande 的中间部分对于保护这种多样化的地方性鱼类群至关重要。