长江中下游湖泊贝类物种濒危状况评估

长江中下游是我国淡水贝类资源分布最为集中的地区.由于人类活动加剧,该区域贝类受到严重威胁.为系统评估贝类物种现状,于2003年5月至2005年6月对13个典型湖泊进行了系统调查.共采集贝类69种,其中中国特有种44种.不同类型湖泊贝类的组成差别较大.通江湖泊的物种明显较丰富,尤其是适应流水生境的种类,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的贝类分别有53种和57种,占总数的76.8%和82.6%.阻隔湖泊的物种较少,在4-19种之间.对67种贝类濒危等级的评价结果表明,近危及受威胁的种类占58.2%,只有37.3%的种类种群稳定.与历史资料相比,该区域贝类的多样性已明显下降,双壳类优势类群由大型的蚌类演变为小型的河蚬.分析显示,贝类资源衰退的主要原因是江湖阻隔、过度捕捞和水体污染等人为干扰.

Assessment of species status of mollusca in the mid-lower Yangtze Lakes

The mid-lower Yangtze River basin has the most diverse molluscan fauna in China. However, owing to the increasing human activities during past decades, molluscs are highly imperiled in this region. Aiming at systematic assessment of status quo of mollusc species, investigations in 13 lakes of mid-lower Yangtze River basin were conducted during May, 2003 to June, 2005. 69 species were identified, of which 44 species were endemic to China. The diversity differed greatly between river-connected and –isolated lakes. Connected lakes were most speciose, especially potamophilus taxa, such as Rivularia spp, Semisulcospira spp and Unionidae. In the two largest connected lakes, Lake Poyanghu and Lake Dongtinghu, the species numbers were 53 and 57, accounting for 76.8% and 82.6% of the total, respectively. In contrast, molluscs in isolated lakes were very species-poor, each with 4-19 species. Quantitative analysis indicated changes on relative abundance of two predominant species (Bellamya purificata and Corbicula fluminea) were consistent with connectivity of research lakes. By calculation of conservation value indices, threatened status of 67 species was evaluated. The results showed that the current status of molluscan fauna in Yangtze Lakes was grim. Of 67 species evaluated, 58.2% were considered near threatened or threatened, of which 26 species were threatened, 13 species were near threatened, and only 37.3% (25 species) were able to maintain stable populations. In comparison with historical records, it was found that the fauna had deteriorated significantly, and the dominant taxa of bivalves had changed from large-sized unionids to the small-sized clam, Corbicula fluminea. The deterioration is considered to be attributed to river-lake isolation, overharvest and water pollution.