我国东部轻度富营养化湖泊（元荡湖）介形类组成及其生态意义

元荡湖是我国东部平原的一个浅水湖泊，原系淀山湖的一个湖湾，后因芦滩封淤而成，其形成历史短，是探讨动物类群组成与湖泊生态系统演化间关系的理想场所。近年由于人类活动频繁，该湖已处于轻度富营养化状态。研究首次对该湖泊中的介形类进行了研究，共发现9种，它们分别是Cypretta turgida、Cypria kraepelini、Cypridopsis vidua、Cypris subglobosa、Dolerocypria taalensis、Fabaeformiscandona myllaina、F. subacuta、Fabaeformiscandona sp.和Ilyocypris salebrosa。这些介形类均非地方性物种，且都对生态环境有较强的耐受性。结合元荡湖母体湖泊-淀山湖水动力大、无介形类生存的实际情况，研究认为元荡湖中的介形类应由周边迁移而来，且其组成已受到人类活动的干扰。优势度（Y）分析结果也显示，C. kraepelini、F. myllaina、F. subacuta和Fabaeformiscandona sp.共4种出现频率相对较高的介形类中，以富营养化指示物种C. kraepelini的优势度最高。而典型对应分析结果（Canonical correspondence analyses，CCA）发现，自然环境因素水深仍是影响介形类分布的主要环境因子，其次是总氮、叶绿素a、水体透明度和溶解氧。通过分析介形类动物的生活习性和摄食方式发现，元荡湖的介形类分属于底栖动物栖息类型中的游泳型（如C. kraepelini和C. vidua）、攀爬型（如C. subglobosa和C. turgida）和蔓生型(其他5种)，其中蔓生型介形类占比最高，达56%，这也解释了为什么在元荡湖这样一个浅水湖泊中水深却成为影响介形类分布的主要环境因素。总结发现，元荡湖中的介形类组成和丰度分布受到湖泊形成时间的长短、自然环境因素和人类干扰等方面的共同影响，这为今后深入开展介形类组成与湖泊演化间的关系提供了理论证据。此外，研究首次报导了F. myllaina在中国的分布。 关键词： 元荡湖；介形类；水深；人为干扰；优势度Y；栖息类型

Ostracod Assemblages and Their Ecological Significance in A New Mildly Eutrophic Lake (Yuandang Lake) in Eastern China

Lake Yuandang, a shallow lake in the East Plain ecoregion of China, was originally part of Lake Dianshan; the deposition of sediments formed a reed beach at the junction between these two lakes one hundred years ago. The lake has become mildly eutrophic,due to increasing anthropogenic pressures. In the present study,nine ostracods(Cypretta turgida,Cypria kraepelini,Cypridopsis vidua, Cypris subglobosa, Dolerocypria taalensis, Fabaeformiscandona myllaina, F. subacuta, another Fabaeformiscandona sp. and Ilyocypris salebrosa ) were found. None of these species are endemic species,and all are highly tolerant to variable environments. In an analysis of the dominance(Y) of the ostracods,four species(C. kraepelini,F. myllaina,F. subacuta and Fabaeformiscandona sp.) were found to have relatively high effective occurrence numbers and,among these,C. kraepelini was the most abundant and dominant species in Lake Yuandang. F. myllaina was originally reported in Japan and this is the first record of the species in China. Canonical correspondence analyses(CCA) showed that water depth was the most important predictor of ostracod occurrence,followed by total nitrogen, chlorophyll a, transparency and dissolved oxygen. Classified according to the habitat traits of zoobenthos,the ostracods in Lake Yuandang included swimmers(C. kraepelini and C. vidua),climbers (C. subglobosa and C. turgida) and sprawlers(the other five species). The sprawlers accounted for 56％ of all the ostracods,which provided an indication of why the water depth played the most important role in determining the abundance and distribution of the ostracods in this shallow lake.Overall, the composition and abundance of ostracods could be influenced by the natural physicochemical factors,increasing human impacts,and be possibly influenced by the short history of this lake. This study expands our knowledge on the relationship between the community composition of ostracod and the evolutions of lake's ecosystems.