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首页> 外文期刊>Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie >Distribution and habitats of Unio caffer Krauss, 1848 (Bivalvia: Unionoida: Unionidae) in South Africa based on the records in the database of the National Freshwater Snail Collection
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Distribution and habitats of Unio caffer Krauss, 1848 (Bivalvia: Unionoida: Unionidae) in South Africa based on the records in the database of the National Freshwater Snail Collection

机译：基于国家淡水蜗牛收藏数据库中的记录，Unio caffer Krauss，1848（Bivalvia：Unionoida：Unionidae）在南非的分布和栖息地

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The distribution of the Unionoida is almost cosmopolitan and reaches its greatest diversity in North America with 860 currently recognized valid species. Two genera of the family Unionidae, Unio and Coelatura, comprising four species, occur in South Africa. This article focuses on the distribution and habitats of Unio caffer Krauss, 1848 based on the records in the database of the National Freshwater Snail Collection (NFSC) of South Africa. This bivalve is considered to be endemic to South Africa and although it was sporadically reported from elsewhere in South Africa, the Western Cape is the only province from which no samples are on record in the database of the NFSC. The majority of the 58 samples on record was recovered from rivers (32.8%) and dams (20.7%) and from water conditions described as perennial, clear and fresh and 22 of the samples were collected in water bodies with a predominantly sandy substratum. A temperature index calculated for this species ranked it in ??? fth position of the 12 bivalve species represented in the database on account of its association with low climatic temperatures. An integrated decision-tree analysis indicated that temperature, substratum and water bodies per se were the most important factors of those investigated that played a signi??? cant role in establishing the geographical distribution of this species in South Africa. Comprehensive surveys for freshwater molluscs conducted by state and local health authorities were discontinued during the eighties of the previous century and the majority of sampling sites have not been revisited since. Therefore hardly any recent data pertaining to the conservation status and species diversity of the mollusc fauna of South Africa are available. However, during relatively recent surveys conducted by the authors at three previously positive sites for U. caffer no specimens of this species could be recovered and it is also reported in literature that its range in the south-western Cape has decreased in recent years. With regard to its conservation status, the above ???ndings seem to suggest that U. caffer should at least be considered as vulnerable a?? if not endangered a?? as reported for some related species elsewhere in the world. Although speculative, several reasons are suggested to explain the global phenomenon of decline in freshwater bivalves. These include, amongst others, construction of impoundments, introduction of alien species, wetland drainage and canalization and pollution. However, the unique lifecycle of the Unionoida could also play an important role in this respect due to the fact that their larval stages are obligatory parasites on ???sh. These bivalves are therefore dependent on ???sh for their survival and dispersal and without their host ???sh populations will disappear. To sustain a viable population a water body should therefore be suitable not only for the bivalves themselves but also for their host ??? sh. As mentioned earlier, the majority of samples of U. caffer were recovered from dams and rivers, water body types both under pressure of over exploitation and pollution. It is therefore recommended that thorough surveys should be planned and conducted in speci???c areas which could be selected with the documented geographical distribution in the database of the NFSC as guideline. A comparison of the results of such surveys with the data in the database of the NFSC could make a considerable contribution towards assessing the current conservation status and diversity of the freshwater molluscs of South Africa.
机译：Unionoida的分布几乎是世界性的，在北美地区拥有860种目前公认的有效物种，达到了最大的多样性。南非有两个科，Unionidae科的两个属，Unio和Coelatura，共有四个物种。本文基于南非国家淡水蜗牛收藏（NFSC）数据库中的记录，着眼于1848年克雷乌斯（Unio caffer Krauss）的分布和栖息地。该双壳类被认为是南非特有的，尽管从南非其他地方偶发报道，但西开普省是唯一一个在NFSC数据库中没有样本记录的省。有记录的58个样品中的大多数是从河流（32.8％）和水坝（20.7％）以及描述为多年生，清澈和新鲜的水环境中回收的，其中22个样品是在主要含沙层的水体中采集的。为该物种计算的温度指数将其排名为???由于其与低气候温度的关系，该数据库中代表的12种双壳类物种的第f位。综合决策树分析表明，温度，基质和水体本身是被调查者中最重要的因素，具有重要意义。不能在建立该物种在南非的地理分布中发挥作用。在上个世纪八十年代，国家和地方卫生当局对淡水软体动物进行的全面调查中断了，此后大多数采样地点都没有再访问。因此，几乎没有关于南非软体动物的保护状况和物种多样性的最新数据。但是，在作者最近对美国的三个阳性地点进行的相对较近的调查中，无法找到该物种的标本，而且据文献报道，其在西南开普省的范围近年来有所减少。关于其保存状态，上述发现似乎表明，美国花椰菜至少应被认为是易受害的。如果不濒临一个？据世界其他地方一些相关物种报道。尽管是推测性的，但提出了一些理由来解释全球淡水双壳类动物数量下降的现象。这些措施除其他外包括建造水库，引进外来物种，湿地排水以及渠化和污染。但是，由于其幼虫阶段是sh的必需寄生虫，因此，Unionoida的独特生命周期在这方面也可能起重要作用。因此，这些双壳类动物的生存和传播依赖于sh，没有它们的宿主，sh种群将消失。因此，为了维持种群的生存能力，水体不仅应适合双壳类动物本身，也应适合它们的宿主。 sh。如前所述，U.caffer的大多数样品是在过度开采和污染的压力下从水坝类型的水坝和河流中回收的。因此，建议在特定区域中计划和进行彻底的调查，可以选择这些区域，并以NFSC数据库中的文件化地理分布作为指导。将此类调查的结果与NFSC数据库中的数据进行比较，可以为评估南非淡水软体动物的当前保护状况和多样性做出巨大贡献。

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