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n Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Verspreiding en habitats van Krauss, 1848 (Bivalvia: Unionoida: Unionidae) in Suid-Afrika gebaseer op die rekords in die databasis van die Nasionale Varswaterslakversameling : navorsings- en oorsigartikels

Volume 29, Issue 4
  • ISSN : 0254-3486
  • E-ISSN: 2222-4173

Abstract

Die kosmopolities-verspreide Unionoida bereik hul grootste diversiteit in Noord-Amerika. In Suid-Afrika word twee genera van die familie Unionidae, naamlik en wat vier spesies insluit, aangetref. Hierdie artikel handel oor die verspreiding en habitats van Krauss, 1848 gebaseer op die rekords in die Nasionale Varswaterslakversameling (NVWSV) van Suid-Afrika. Alhoewel dit elders in Suid-Afrika sporadies aangetref is, is die Wes-Kaap die enigste provinsie waarvan geen monster op rekord in die databasis van die NVWSV is nie. Van die 58 monsters wat op rekord is, is die meerderheid in riviere (32.8%) en damme (20.7%) versamel en in watertoestande wat as standhoudend, staande, helder en vars beskryf is. 'n Temperatuur-indeks wat vir hierdie spesie bereken is, het dit vyfde in rangorde geplaas van die 12 Bivalvia-spesies wat in die databasis verteenwoordig word op grond van 'n assosiasie met lae omgewingstemperature. 'n Besluitnemingsboom-analise het aangedui dat temperatuur, substratum en waterbronne die mees betekenisvolle bydrae gelewer het tot die daarstelling van die gedokumenteerde geografi ese verspreiding van . Omdat omvattende opnames van varswater Mollusca deur staatsinstansies reeds in die tagtigerjare van die vorige eeu uitgefaseer is en die meerderheid versamelpunte sedertdien nie weer gemonster is nie, is kennis oor hul huidige stand van bewaring en spesiediversiteit gebrekkig. Negatiewe resultate by drie voormalige lokaliteite van wat wel intussen deur die outeurs besoek is, dui egter daarop dat die voortbestaan daarvan, soos van sommige verwante spesies elders in die wêreld, bedreig word. Dit word bepleit dat opnames van varswater Mollusca met die gedokumenteerde verspreiding in die databasis van die NVWSV as riglyn, beplan en uitgevoer behoort te word. Die resultate van sulke opnames behoort 'n groot bydrae te lewer om die huidige stand van die verspreiding en spesiediversiteit van die varswater Mollusca van Suid-Afrika sinvol te evalueer.


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 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 fifth 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 significant 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 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 findings seem to suggest that should at least be considered as vulnerable - if not endangered - 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 fish. These bivalves are therefore dependent on fish for their survival and dispersal and without their host fish 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 fish. As mentioned earlier, the majority of samples of 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 specific 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.

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/content/aknat/29/4/EJC20483
2010-12-01
2019-08-24

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