'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
Date
2015Author
Wolmarans, Cornelius T.
Wepener, Victor
Pretorius, Uané
Erasmus, Johannes H.
De Kock, Kenne N.
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Die hoogste getal gedokumenteerde uitsterwings van enige belangrike taksonomiese groep
word aan die Mollusca toegedig. Faktore wat hoofsaaklik hiervoor verantwoordelik is, sluit
onder meer omgewingsveranderinge en antropogeniese impakte in wat tot die tot niet gaan
van die habitat aanleiding gee. Daarbenewens is die bewaringstatus van minder as 2% van die
ongeveer 7000 molluskspesies wêreldwyd bekend tot dusver nog nie behoorlik geassesseer
nie. Die doel van die huidige ondersoek wat in 2014 uitgevoer is, was om die molluskdiversiteit
van die Mooirivier met die resultate van 1963 te vergelyk. Dit is gedoen deur ’n opname
uit te voer van die molluskdiversiteit by dieselfde lokaliteite as in 1963. Twee opnames is
gemaak tydens ’n vroeë- en laatlaagvloeiperiode in 2014 by agt lokaliteite wat met dié van
die 1963-opnames ooreenstem. Die pH, elektriese geleiding (EG) en temperatuur is ook by
elk van die lokaliteite gemeet. Die identiteit van die 14 slakspesies wat in 1963 gevind is, het
ooreengestem met 14 van die 15 in 2014. Die uitheemse indringerspesie Physa acuta is tydens
die 2014-opname vir die eerste keer in hierdie rivier gevind, waarskynlik weens ’n toename in
organiese verryking. In die 1963-opname is Burnupia mooiensis en Pisidium langlyanum by die
meeste lokaliteite gevind, en in 2014 Gyraulus connollyi en Ferrissia cawstoni. Die meeste van die
molluske uit hierdie gebied wat voorheen op rekord gestel is, is in 2014 gevind. Die pH wat
in 2014 ’n geringe tot aansienlike verlaging getoon het, word aan mynversuring toegeskryf
en het nie ’n merkbare invloed op die molluskdiversiteit gehad nie. Die hoër elektriese
geleiding wat tydens die 2014-opname gemeet is, het vanweë die verdraagsaamheid van
varswatermolluske in hierdie verband, ook geen verandering in die molluskdiversiteit teweeg
gebring nie. Die temperatuur was in die laatlaagvloei deurgaans hoër. Ondanks die feit dat
hierdie studies vyf dekades uitmekaar gedoen is en antropogeniese impakte toegeneem het, is
geen noemenswaardige verandering in die molluskdiversiteit waargeneem nie 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
URI
http://hdl.handle.net/10394/18856http://dx.doi.org/10.4102/satnt.v34i1.1294
http://www.satnt.ac.za/index.php/satnt/article/view/1294