n Vergelyking van die Mollusca-diversiteit in die Mooirivier (Noordwes-Provinsie) soos gevind met opnames wat gemaak is in 1963 en weer 50 jaar later/A comparison of the Mollusca diversity in the Mooi River (North-West Province) as found during surveys conducted in 1963 and again 50 years later

• Published in: Suid-Afrikaanse tydskrif vir natuurwetenskap en tegnologie 2015-01, Vol.34 (1), p.1
• Main Authors: Wolmarans, Cornelius T, Wepener, Victor, Pretorius, Uané, Erasmus, Johannes H, de Kock, Kenné N
• Format: Article
• Language: Afrikaans
• Subjects: Biological diversity; Comparative studies; Habitats; Mollusks
• ISSN: 0254-3486; 2222-4173

The highest number of documented extinctions of any major taxonomic group is ascribed to the Mollusca. Factors mainly responsible for this include environmental changes and anthropogenic impacts which result in habitat destruction. Furthermore, the conservation status of less than 2% of the more or less 7000 mollusc species, known worldwide, is still not properly assessed. The aim of the study done in 2014 was to assess the current status of the mollusc diversity in the Mooi River and to compare the results to the study done in 1963. The eight sites selected for this survey correspond with sites surveyed during the 1963 study, with surveys conducted during both an early and late low-flow period. The pH, electrical conductivity (EC) and temperature were also measured at each locality. Of the 15 mollusc species collected in 2014, altogether 14 were the same as in the 1963 survey. However, an alien invasive species Physa acuta was additionally collected during the current survey, which is probably due to an increase in organic enrichment. During the 1963 survey Burnupia mooiensis and Pisidium langlyanum were present at most of the sites, while Gyraulus connollyi and Ferrissia cawstoni were found at six of the eight sites during the 2014 survey. Most of the molluscs previously recorded, were still present in 2014. With regard to the abiotic factors, the pH values recorded in 2014 showed a moderate to large decrease as compared to the 1963 survey. This acidification is ascribed to the development of gold mines in the adjacent area and apparently had little influence on the mollusc diversity. The increase in EC measured in 2014 did not have any influence on the diversity of the molluscs, probably due to their wide tolerance for this factor. As expected, the temperature measured in 2014 was markedly higher during the late low-flow period as compared to the early low-flow period. In conclusion, the differences discussed above revealed no obvious influence on the diversity of the freshwater molluscs over a 50 year period, despite increased anthropogenic impacts.