In China,the most diverse molluscan fauna occurs in the Yangtze basin.The molluscan fauna in this region are highly imperiled due to increasing human activities.Aiming at effective conservation of the deteriorating molluscan fauna, intensive field investigations of freshwater molluscs on the mid-lower Yangtze Lakes were conducted between June,2003 and May,2005.Altogether 69 species were identified during the collection,including 29 gastropod species belonging to 9 families,40 bivalve species belonging to 5 families,and 42 endemic species.Among them,Unionidae and Viviparidae are the two families with the highest species numbers.accounting for 50.7%and 14.5%ofthe total,respectively.The diversity varies greatly from take to lake.River-connected lakes contain the most diverse fauna,especially those adapted to lotic habitat,su as Rivularia spp,Semisulcospira spp and some cies of Unionidae.In the two large river-connected lakes,Poyang Lake and Dongting Lake,there are 66 species and 40 endemic species,accounting for 95.7% of the total species number and 95.2% of the total endemic species number, respectively.In contrast,the historical records,it is found that total species number and endemic species number decreased greatly,with a loss of about 50% of the historical records.Meanwhile,the distribution ranges of most taxa were also shrunk.Habitat loss and hydrological alteration in the Yangtze Potamo-lacustrine Complex Ecosystem caused by river-lake isolation should be the primary factor causing the decline of molluscan fauna.Other human activities, such as overharvesting,reclamation and pollution,may be also the important factors.%长江中下游流域是我国淡水贝类多样性最为集中的地区,然而由于人类活动的影响,淡水贝类已成为高度濒危的类群.为有效保护淡水贝类的多样性,我们于2003年6月.2005年5月对长江中下游流域13个水体软体动物的多样性及分布进行了调查.共采集到软体动物69种(中国特有种42种),隶属于腹足类9科14属29种和瓣鳃类5科17属40种.其中,蚌科和田螺科是种类数最多的两个科,分别占总种类数的50.7%和14.5%.不同类型湖泊软体动物种类数的差别较大.通江湖泊所占种类数相对丰富,尤其是适应流水的种类,如河螺属、短沟蜷属及蚌科的种类.大型通江湖泊鄱阳湖和洞庭湖软体动物的种类数和特有种数分别66种和40种,分别占总种类数和总特有种数的95.7%和95.2%.阻隔水体所占种类数相对较少,种类数为4-19种.与历史资料相比,长江中下游湖泊软体动物的种类数和特有种数均减少50%左右,且多数种类的分布范围也明显缩小.造成贝类资源衰退的可能原因主要是江湖阻隔所引起的整个江湖复合系统栖息地和水文情势的改变,其他的人为活动如过度捕捞、围垦及废污水的过度排放等也可能是其中的重要原因.
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