ISSN 0075-6458 39 Koedoe 49/2 (2006) The current status of freshwater molluscs in the Kruger National Park C.T. Wolmarans and K.N. de KocK Wolmarans, C.T. and K.N. de Kock. 2006. The current status of freshwater molluscs in the Kruger National Park. Koedoe 49(2): 39–44. Pretoria. ISSN 0075-6458. Surveys regarding the freshwater mollusc population of the Kruger National Park com- menced before 1966 and was repeated in 1995, 2001 and recently in 2006. During this period the park was exposed to several droughts as well as floods, all of which could have had some influence on the various habitats in the park. Industrial developments and urbanisation near some of the major rivers outside the park, but which flow through the park, could also have a detrimental effect on the species diversity of the freshwater molluscs. The recent survey in 45 habitats included several dams and rivers. The survey was done to determine the current status of the mollusc species diversity. By comparing it with previous surveys, an attempt was made to establish the overall health of fresh- water mollusc habitats. From the results it is clear that there was a drastic decrease in the mollusc species diversity in five of the habitats. Although there was a slight change in the species composition in some of the major rivers there was no difference in the number of species collected in these habitats. Tarebia granifera, an alien invader mol- lusc, was found in several rivers and dams. Gyraulus costulatus, Melanoides victoriae and Eupera ferruginea, which could not be found during the survey of 2001, were col- lected during the current survey. Key words: freshwater molluscs, species diversity, rivers, dams, alien invaders. C.T. Wolmarans and K.N. De kock, School of Environmental Sciences and Develop- ment (Zoology), North-West University, Potchefstroom Campus, P/Bag X6001, Potchef- stroom, 2520 Republic of South Africa. ISSN 0075-6458 39 Koedoe 49/2 (2006) Introduction The largest diversity of freshwater molluscs is usually present in the tropical and sub- tropical areas of the world (De Kock et al. 2002). In South Africa, this is especially true for Mpumalanga, Limpopo and KwaZulu- Natal (De Kock & Wolmarans 1998). The Kruger National Park is situated within the first two provinces mentioned. Various spe- cies of freshwater snails act as intermediate hosts for trematode parasites (De Kock & Wolmarans 1998) while they are also known for their ability to act as indicators for water health (Schoonbee 1963). The poor ability of these organisms to migrate, makes them vulnerable to changes in their habitats, such as global warming, pollution or prolonged periods of drought. Although the influence of some of these factors like global warm- ing, is difficult to determine over the short to medium term, the influence of other factors like environmental contamination, may be more evident over a shorter period of time. The degree of these influences on molluscs may also be influenced by a stream, river, small pond or dam. Although the Kruger National Park is recognised worldwide for its conservation efforts, it is not isolated from the factors mentioned above. A number of rivers in the park, including the Letaba, Olifants, Crocodile, Sand and Sabie, mean- der through adjacent, highly populated and industrialised areas and is it possible that the changes in the water quality occurring in these areas have an effect on the freshwater biodiversity in the park. Molluscs present in isolated habitats may, however, escape such changes. The aim of this investigation was to determine the current status of freshwater molluscs in the park and to compare this with a survey done in 2001. Wolmarans.indd 39 2006/10/15 10:59:49 PM Koedoe 49/2 (2006) 40 ISSN 0075-6458 Methods and materials This study concentrated mainly on water bodies that had been surveyed for molluscs during the 2001 col- lection. A few habitats, namely the Mtombeni Spruit, Rabelais Dam (does not exist any more), Lower Sabie rest camp, Tsende Drift, Skukuza fish pond and Jones’s Dam were not surveyed. Habitats sur- veyed for the first time included the Mpanamana Dam, Timbavati River below the Piet Grobler Dam wall, Sabie River below the Lower Sabie Dam wall, Crocodile River, Mbyamiti River (weir), and the Let- aba River below the Engelhard Dam wall. A total of 45 habitats were surveyed during 2006. All of these habitat types were screened for molluscs by means of aluminium mollusc scoops. Although a quantita- tive survey of molluscs was not intended, the same time (man hours) was spent at each of these habitats as in previous surveys in order to recover as many species as possible. The molluscs collected at each habitat were largely full-grown specimens and were transferred to 50 ml glass screw-capped bottles and fixed in 70 % ethanol. Each bottle was provided with a label containing information on date of collection, locality, and collection number. The specimens were identified by means of a stereo microscope and were then added to the National Freshwater Snail Collec- tion (NFSC) located at the North-West University, Potchefstroom Campus. Results The results of this investigation are pre- sented in Table 1. From this it is evident that 11 of the habitats, namely the Crocodile River, Mpanamana Dam, Nhlanganzwane Dam, Ngotso Dam, Letaba River below the Engelhard Dam, Olifants River, Lower Sabie Dam, the Sabie River below the Lower Sabie Dam, the Mbyamiti River (weir), Luvuvhu River and Leeupan were not surveyed in 2001. This was mainly due to a lack of suit- able habitats at that time and the fact that some of the habitats were situated in con- cession areas. Of the 45 habitats surveyed in 2006, no molluscs were found in 12 of the habitats, i.e., the Mpanamana, Nhlan- ganzwane and Ngotso Dams (not surveyed previously), the Nsemani Dam, Shisa Spruit, Vervoer Dam, Manzimahle Dam, Sunset Dam, Sable Dam, Silolweni Dam, Leeupan and the Luvuvhu River. Comparing the 34 habitats surveyed in both 2001 and 2006, it is evident that only the Piet Grobler Dam had no molluscs in 2001. Contrary to this, no molluscs were found in seven of these habitats in 2006, namely the Shisa Spruit, the Nsemani, Vervoer, Manzimahle, Sunset, Sable and Silolweni Dams, four species, not found in 2001 were collected in 2006. Tare- bia granifera (an alien invader snail) was found in 12 habitats including several rivers and dams (Table 1). According to the records of the NFSC this species was not previously found in the Kruger National Park. The other three species, namely Gyraulus costulatus, Eupera ferruginea and Melanoides victoriae were found in numerous habitats during the first extensive survey done in 1964. Eupera ferruginea was also found during the 1995 survey. Lanistes ovum and Pisidium pirothi, collected in 2001, were not found during the recent survey. In comparison with the 2001 survey, there was a drastic decrease in the species diversity evident in five of the habitats surveyed in 2006. These include the Matjulu and Shisa spruits, the Engelhard Dam, the Nwanetsi water hole and the Gud- zani and Sirheni dams. Whether the presence of the invader T. granifera played a role in the decrease in three of these habitats, name- ly the Engelhard Dam, Nwanetsi water hole and the Gudzani Dam is unknown as it was not found in the remaining three habitats. A drastic increase in species diversity was not experienced in any of the habitats surveyed in 2006. The major rivers (Timbavati, Letaba, and Sabie), showed no significant difference in the mollusc species diversity between the two surveys. Discussion Direct comparisons of the species diversity recorded during the respective surveys could lead to scientifically unfounded conclusions. Aspects that should be taken into account, include amongst others, the number of col- lections made in a habitat, the exact collec- tion site, the time of the year when the collec- tion was made, as well as the rainfall patterns prior to each survey (De Kock & Wolmarans 1998). In spite of this, it still seems possible to outline specific trends. Although there was no obvious differences in the number of Wolmarans.indd 40 2006/10/15 10:59:49 PM ISSN 0075-6458 41 Koedoe 49/2 (2006) Table 1 Molluscs found in water bodies of the Kruger National Park surveyed in 2001 and 2006 Rainfall moni- toring station Collection site Grid reference Species collected in 2006 Species collected in 2001 Berg-en-Dal Matjulu Spruit 25º21’S; 31º31’E Bulinus globosus Bulinus globosus Biomphalaria pfeifferi Bulinus forskalii Lymnaea columella Biomphalaria pfeifferi Lymnaea natalensis Lymnaea columella Aplexa marmorata Burnupia caffra Melanoides tuberculata Mlambane Spruit 25º21'S; 31º31'E Bulinus globosus Bulinus forskalii Biomphalaria pfeifferi Aplexa marmorata Crocodile Bridge Gezantombi Dam 25º20'S; 31º52'E Bulinus forskalii Bulinus forskalii Cleopatra ferruginea Lymnaea columella Aplexa marmorata Burnupia caffra Crocodile River 25º21'S; 31º54'E Tarebia granifera (Not surveyed) Mpanamana Dam 25º17'S; 32º0'E No molluscs found (Not surveyed) Nhlanganzwane Dam 25º14'S; 31º57'E No molluscs found (Not surveyed) Houtboschrand Timbavati River 24º31'S; 31º38'E Bulinus globosus Bulinus africanus Lymnaea natalensis Lymnaea natalensis Gyraulus costulatus Burnupia caffra Ngotso Dam 24º11'S; 31º43'E No molluscs found (Not surveyed) Letaba Letaba River 23º45'S; 31º22'E Lymnaea collumella Bulinus forskalii Physa acuta Physa acuta Aplexa marmorata Melanoides tuberculata Melanoides tuberculata Engelhard Dam 23º50'S; 31º28'E Physa acuta Bulinus globosus Aplexa marmorata Bulinus tropicus Tarebia granifera Bulinus forskalii Biomphalaria pfeifferi Physa acuta Melanoides tuberculata Corbicula fluminalis Pisidium pirothi Letaba River below the 23º31'S; 31º39'E Lymnaea columella (Not surveyed) Engelhard Dam wall Physa acuta Melanoides tuberculata Melanoides victoriae Tarebia granifera Corbicula fluminalis Lower Sabie Olifants River 24º31'S; 31º41'E Physa acuta (Not surveyed) Mpondo Dam 25º12'S; 31º43'E Bulinus forskalii Bulinus forskalii Tarebia granifera Lymnaea natalensis Ceratophallus natalensis Lymnaea collumella Bulinus forskalii Spathopsis petersi Wolmarans.indd 41 2006/10/15 10:59:50 PM Koedoe 49/2 (2006) 42 ISSN 0075-6458 Lower-Sabie Dam 25º07'S; 31º56'E Tarebia granifera ( Not surveyed ) Sabie River 25º07'S; 31º55'E Bulinus forskalii Physa acuta Burnupia cf. caffra Apexa marmorata Sabie River below 25º07'S; 31º55'E Tarebia granifera ( Not surveyed ) Lower Sabie Dam wall Corbicula fluminalis Eupera ferruginea Mooiplaas Pioniers Dam 23º31'S; 31º23'E Bulinus globosus Bulinus globosus Biomphalaria pfeifferi Bulinus forskalii Lymnaea natalensis Biomphalaria pfeifferi Grootvlei Dam 23º20'S; 31º30'E Bulinus tropicus Spathopsis sp Nwanetsi Nwanetsi water hole 24º28'S; 31º58'E Biomphalaria pfeifferi Bulinus globosus Tarebia granifera Bulinus tropicus Bulinus forskalii Biomphalaria pfeifferi Ceratophallus natalensis Burnupia caffra Spathopsis wahlbergi Spathopsis petersi Corbicula fluminalis Melanoides tuberculata Oxyloma striata Gudzani Dam 24º22'S; 31º55'E Bulinus globosus Bulinus globosus Biomphalaria pfeifferi Bulinus tropicus Lymnaea natalensis Biomphalaria pfeifferi Melanoides tuberculata Lymnaea natalensis Tarebia granifera Ceratophallus natalensis Melanoides tuberculata Spathopsis petersi Corbicula fluminalis Pretoriuskop Mbyamiti River 25º13'S; 31º34'E Bulinus globosus Bulinus globosus Biomphalaria pfeifferi Lymnaea columella Aplexa marmorata Mbyamiti River (weir) 25º15'S; 31º37'E Bulinus globosus ( Not surveyed ) Biomphalaria pfeifferi Tarebia granifera Mestel Dam 25º06'S; 31º12'E Bulinus globosus Bulinus globosus Melanoides tuberculata Lymnaea columella Tarebia granifera Aplexa marmorata Shitlehave Dam 25º08'S; 31º19'E Bulinus forskalii Biomphalaria pfeifferi Menanoides tuberculata Punda Maria Klopperfontein Dam 22º37'S; 31º10'E Aplexa marmorata Bulinus tropicus Bulinus forskalii Satara Nkaya Pan 24º31'S; 31º45'E Bulinus forskalii Bulinus forskalii Piet Grobler Dam 24º31'S; 31º38'E Bulinus globosus No molluscs found Tarebia granifera Timbavati River below Piet Grobler Dam wall 24º30'S; 31º38'E Tarebia granifera Bulinus forskalii Nsemani Dam No molluscs found Bulinus forskalii Burnupia caffra Table 1 (continued) Wolmarans.indd 42 2006/10/15 10:59:50 PM ISSN 0075-6458 43 Koedoe 49/2 (2006) Shingwedzi Krapkuil Dam 23º14'S; 31º18'E Bulinus tropicus Burnupia caffra Sirheni Dam 22º56'S; 31º14'E Bulinus globosus Bulinus globosus Biomphalaria pfeifferi Biomphalaria pfeifferi Lymnaea natalensis Lymnaea columella Lanistes ovum Shisa Spruit 22º57'S; 31º15'E No molluscs found Cleopatra ferruginea Melanoides tuberculata Spathopsis petersi Corbicula fluminalis Kanniedood Dam 23º08'S; 31º27'E Spathopsis wahlbergi Bulinus tropicus Spathopsis petersi Bulinus forskalii Lymnaea natalensis Skukuza Olifantdrinkgat 24º53'S; 31º44'E Bulinus forskalii Bulinus forskalii Vervoer Dam 25º07'S; 31º29'E No molluscs found Lymnaea columella Aplexa marmorata Manzimahle Dam 24º53'S; 31º43'E No molluscs found Bulinus forskalii Sunset Dam 25º06'S; 31º54'E No molluscs found Aplexa marmorata Phalaborwa Sable Dam 23º56'S; 31º14'E No molluscs found Bulinus tropicus Bulinus forskalii Orpen Dam 24º47'S; 31º53'E Aplexa marmorata Lymnaea columella Ceratophallus natalensis Mazithi Dam 24º43'S; 31º50'E Bulinus forskalii Bulinus forskalii Kumana dam 24º37'S; 31º47'E Bulinus forskalii Bulinus forskalii Nwaswitsontso River 24º37'S; 31º47'E Bulinus forskalii Bulinus forskalii Silolweni Dam 24º29'S; 31º50'E No molluscs found Bulinus forskalii Burnupia caffra Leeupan 24º50'S; 31º48'E No molluscs found (Not surveyed) Pafuri Luvuvhu River 22º26'S; 31º13'E No molluscs found (Not surveyed) species found in the larger rivers (Timbavati, Letaba and Sabie Rivers) when comparing the 2001 and 2006 surveys, slight changes in the species diversity were evident (Table 1). This may be an indication that any changes in the water quality of these rivers before entering the park, still did not have a notice- able effect on the mollusc species diversity in these habitats. The presence of Physa acuta (also known as the sewage snail, Apple- ton 2003) the second-most successful alien invader mollusc species in South Africa (De Kock et al. 1989) in the Olifants River, may be an indication of the abnormal conditions in this river. The unfavourable pH of the water due to old mine activities, the pollution con- tributed by various industries in the Witbank area, and poor farming practises where over- grazing causes top soil to wash into the river, all create a situation where P. acuta may be Table 1 (continued) Wolmarans.indd 43 2006/10/15 10:59:50 PM Koedoe 49/2 (2006) 44 ISSN 0075-6458 one of the few species able to survive. The occurrence of a number of floods in this river since 1995 should have enhanced the overall water quality but did not contribute much to the increase in species diversity of molluscs recovered. The fact that there was a decrease in species diversity of molluscs in a number of habitats and that no snails were found in several of the dams also surveyed in 2001 (Table 1) could either be ascribed to a decrease in the overall number of molluscs in these dams due to a lack of suitable habitats or to environmental influences like specific rainfall patterns directly before the survey. As these dams are not connected to rivers arising outside the park, it seems highly improbable that industrial pollution could play a signifi- cant role in this phenomenon. The presence of T. granifera in a number of habitats in which it was not previously found, could be reason for great concern especially if its pres- ence would have a detrimental effect on the survival of other freshwater fauna. This is an aspect that should, in our opinion, be investi- gated in great depth. Although the increase in species diversity found in 2001 as compared to the survey of 1995 was ascribed to the high rainfall average between 1995 and 2001 (De Kock et al. 2002) the recent survey was done shortly after a period of high rainfall. It is, however, important to keep in mind that the actual period between the last significant rainfall and the time of the survey may play a role in the species diversity and it is there- fore premature to conclude that there was a decrease in the general species diversity as far as the freshwater molluscs are concerned. Therefore more surveys should be done to clarify the reasons for the decrease in species diversity recently encountered. Conclusions Comparisons between the respective habitats surveyed in 2001 and 2006 revealed slight differences in the mollusc species diversity of the Letaba, Timbavati and Sabie Rivers but no differences in the number of species collected. Although there was a decrease in the mollusc species diversity in five of the habitats during the 2006 survey and no molluscs were found in another 12 habitats as compared to only one during the 2001 survey, it would seem premature to conclude that there was an overall decrease in the spe- cies diversity. The occurrence of T. granifera in 12 of the habitats is a matter of concern especially because of its ability to invade a variety of habitats in a relatively short period, a situation that should be monitored very closely in the future. Acknowledgements The authors wish to thank the following persons and institutions for their assistance: The National Parks Board for permission to conduct the research, as well as for their financial support; Mr Hendrik Sithole who was instrumental in assisting us with the necessary arrangements for the survey; the Research Focus Area, Environmental Science and Sustainable Management of the Potchefstroom Campus of the North-West University for financial support. References Appleton, C.C. 2003. Alien and invasive fresh water Gastropoda in South Africa. African Journal of Aquatic Science 28: 69–81. De KocK, K.n., p.H. Joubert & S.J. pretoriuS. 1989. Geographical distribution and habitat pref- erences of the invader freshwater snail species Lymnaea columella (Mollusca: Gastropoda) in South Africa. Onderstepoort Journal of Veteri- nary Research 56: 271–275. De KocK, K.N. & C.T. WolmArAnS. 1998. A re-eval- uation of the occurrence of freshwater molluscs in the Kruger National Park. 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