西沙群岛七连屿珊瑚礁鱼类的物种组成与演替

Species composition and succession of coral reef fishes on Qilianyu Island,Xisha Islands

七连屿是西沙群岛东北面的一个珊瑚礁群岛,生物多样性极高,近年来由于受到了人类扰动影响,鱼类资源出现明显衰退。为探究这一衰退演变特征并更好地保护和管理七连屿珊瑚礁鱼类资源,我们于2018–2023年采用潜水捕捞、渔捞日志记录、水下视频拍摄以及环境DNA分析等方法,并结合近年这一海域的研究资料,对其鱼类种类组成的现状进行分析。结果如下:2017年至今,七连屿共发现珊瑚礁鱼类412种,隶属于2纲16目60科168属,其中鲈形目鱼类最多,为320种,科水平隆头鱼科种类最多,有47种。七连屿以小型鱼类为多;食性方面以肉食性鱼类为多。2021–2023年大中型鱼类比例及肉食性鱼类比例较2017–2020年出现下降,同时小型鱼类和植食性鱼类比例却出现显著上升。两时间段肉食性鱼类相似性较低,为不相似;植食性鱼类相似性较高,为中等相似;小型鱼类相似性较低,为不相似,大型鱼类也为不相似。优势种中大型鱼类和小型鱼类的种类数显著低于稀有鱼类,肉食性鱼类的种类数也显著低于稀有鱼类,而植食性鱼类的种类数则显著高于稀有鱼类。两时间段的鱼类平均分类差异指数(Delta+)和变异分类差异指数(Lambda+)呈下降趋势。以上表明七连屿珊瑚礁鱼类受到了过度捕捞和生境退化的双重影响,鱼类物种发生了显著的更替。研究为今后预测七连屿珊瑚礁鱼类物种演替趋势提供了基础数据,为西沙珊瑚礁生态系统保护和修复提供了参考。

Aims:Qilianyu Island,situated within the northeastern region of the Xisha Islands,harbors rich coral reef ecosystems.However,overfishing and habitat degradation have led to a significant decline in coral reef fish resources.To aid in the conservation and management of these resources,this study aimed to summarize the current composition of coral reef fish on Qilianyu Island and short-term species dynamics.Methods:A continuous survey of coral reef fish from 2018 to 2023 was conducted on Qilianyu Island,utilizing data compiled from various research methods,including diving surveys,fishing logs,underwater videos,and environmental DNA analysis.Fish species were categorized based on feeding habits(herbivores,carnivores,and omnivores)and individual size(small,medium,and large).Human disturbance impacts were assessed using classification diversity and similarity indices.Results:Since 2017,a total of 412 coral reef fish species have been identified on Qilianyu Island,representing 2 classes,16 orders,60 families,and 168 genera.Perciformes comprised the highest number of species(320),with Labridae being the most abundant family(47 species).Small fish species dominated the coral reef fish community,while carnivorous fish being the most prevalent in terms of diet.However,there has been a notable decrease in the proportion of large and medium-sized fish,as well as carnivorous species,from 2017-2020 compared to 2021-2023,accompanied by a significant increase in small and herbivorous fish.The dissimilarity indices between the two periods revealed changes in species composition and diversity.The study revealed that herbivorous fish exhibited the highest similarity,with a moderate level of similarity observed,indicating relatively stable composition over time.Conversely,small fish displayed the lowest similarity,suggesting significant variability in their presence between time periods.Large fish showed dissimilarity,indicating notable shifts in their abundance and composition.Furthermore,dominant fish species exhibited a lower number of large and small fish species compared to rare fish species,suggesting a more diverse composition among less abundant species.Additionally,dominant fish species had fewer carnivorous species but a higher number of herbivorous species compared to rare fish species,indicating potential impacts on trophic interactions within the community.Moreover,both Delta+and Lambda+indices decreased during the two time periods,suggesting a decline in overall species turnover and evenness over time,potentially reflecting ongoing disturbances to the coral reef ecosystem.Conclusions:Our study reveals the coral reef fish community of Qilianyu Island has undergone significant changes due to overfishing and habitat degradation,leading to altered fish species composition and succession patterns.The study provides essential data for predicting future trends in fish species succession within Xisha Coral Reefs and offers insights into the conservation and restoration of these ecosystems.