Abstract
The conservation status of less than 2% of the more or less 7000 mollusk species known worldwide have been properly assessed. Consequently the general level of imperilment is poorly documented and almost certainly underestimated. Freshwater mollusks live permanently in water, have limited means of movement and are exposed to a variety of anthropogenic waste products due to the fact that waterbodies often act as sinks for a large array of harmful pollutants. The Olifants River is often described as one of the most polluted rivers in Southern Africa and is progressively subjected to extremely high pressure with regard to natural resources and associated rural transformation and pollution. Little is on record regarding the diversity of the Mollusca in the Olifants River; therefore, in the present study, four surveys of the molluscs were conducted in this river and selected tributaries during two consecutive years at three localities situated on the Highveld and four localities situated in the Lowveld respectively. The pH and electric conductivity of the water were determined during each survey at each one of the localities and values ranged from 6.93 to 9.50, and 110 µS to 1336 µS, for pH and conductivity respectively. A total of 25 mollusk species were collected during the four surveys which included the exotic invader species Lymnaea columella, Physa acuta, Aplexa marmorata and Tarebia granifera. The latter species yielded the highest number of specimens by far, mainly at a locality which could be described as largely transformed. The results of this investigation can serve as a point of departure for future surveys to evaluate the impact of anthropogenic disturbances on the mollusc diversity in the Olifants River and catchment.
Highlights
Postal address: Unit for Environmental Sciences and Management, Potchefstroom Campus of the North-West University, Private Bag X6001, Potchefstroom 2520, South Africa
Die pH en elektriese geleidingsvermoë van die water is by elk van die lokaliteite bepaal en het gewissel tussen 6.93 en 9.50, en 110 μS en 1336 μS, vir pH en geleidingsvermoë onderskeidelik. ’n Totaal van 25 molluskspesies is tydens die vier opnames versamel wat die eksotiese indringerspesies Lymnaea columella, Physa acuta, Aplexa marmorata en Tarebia granifera insluit
Little is on record regarding the diversity of the Mollusca in the Olifants River; in the present study, four surveys of the molluscs were conducted in this river and selected tributaries during two consecutive years at three localities situated on the Highveld and four localities situated in the Lowveld respectively
Summary
Korttermynbedreigings vir varswater-Mollusca in die Olifantsrivier en enkele sytakke. Die resultate van hierdie ondersoek kan as basis vir toekomstige opnames dien om die impak van antropogeniese versteurings op die diversiteit van die Mollusca in die Olifantsrivier- en opvanggebied te evalueer. A total of 25 mollusk species were collected during the four surveys which included the exotic invader species Lymnaea columella, Physa acuta, Aplexa marmorata and Tarebia granifera The latter species yielded the highest number of specimens by far, mainly at a locality which could be described as largely transformed. Die feit dat waterbronne as stortplek gebruik word vir ’n verskeidenheid van antropogeniese afvalstowwe en dat varswatermolluske permanente waterbewoners is, wat oor beperkte voortbewegingsvermoë beskik, kan moontlik tot bogenoemde statistieke bydra. Rekords van die Nasionale Varswaterslakversameling toon dat daar tot dusver beperkte opnames in hierdie rivierstelsel gedoen is en daar dus min inligting aangaande die diversiteit van molluske in die rivier bestaan. In die huidige ondersoek is gevolglik ’n intensiewe opname van die molluske gemaak by geselekteerde, toeganklike lokaliteite om die gebrekkige kennis betreffende hul diversiteit in die Olifantsrivier aan te vul
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