中文摘要：

通过新的方法（即潜水调查法）调查了西沙群岛浅水区的礁栖鱼类，并从食性角度分析鱼类群落特征及其对水质环境变化的响应。2006年5-6月，对西沙群岛6个岛礁（东岛、永兴岛、羚羊礁、金银岛、华光礁和中建岛）共10个站位的礁栖鱼类种类、数量和长度进行了调查，结合公开资料（FishBase等）确定鱼类食性。共记录到29科71属119种鱼，其中50种是新记录。至此，西沙群岛的鱼类总记录已达到717种。从不同站位来看，永兴岛西的种类数量和Shannon-Wiener多样性指数均最高。多数鱼种分布范围狭小。摄食浮游动物和底栖无脊椎动物的鱼类是优势类群，而草食性、杂食性和食物链顶端食性的鱼类数量和生物量较低，反映出西沙群岛珊瑚礁生态系统整体上健康稳定。永兴岛的杂食性鱼类的数量比例和生物量比例均高于其他岛礁，反映出鱼类群落已对水体富营养化产生响应。

英文摘要：

The aims of our study were to （1） uncover new reef fish species records using the underwater visual census method; and （2） analyze the fish community structure according to trophic groups and its response to water quality changes. The fishes on six reefs （Yongxing Island, Dongdao Island, Lingyang Atoll, Jinyin Island, Huaguang Atoll, and Zhongjian Island） along the Xisha Archipelago were investigated in May-June, 2006 using underwater visual censuses. The fishes we recorded belong to 29 families, 71 genera and 119 species. The number of newly recorded species was 50. The number of fish species increased to 717 in the Xisha area since the 1950＇s. The species number and Shannon-Wiener diversity were both highest on the western reef of Yongxing Island. Most fish species were distributed narrowly in small areas. The dominant assemblages were the planktivores and bottom invertebrate feeders. The rare assemblages were the herbi- vores, the omnivores, and the top predator, the piscivores. The structure of trophic groups indicated that most coral reef systems were relatively healthy. The percentage of total abundance （and biomass） comprised by omnivores was largest on the western reef of Yongxing Island compared to other reefs, suggesting that the fish community structure had responded to water eutrophication around Yongxing Island.