n Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Verspreiding van die inheemse mossel Connolly 1931 (Bivalvia : Sphaeriidae) met betrekking tot temperatuur, reënval en water tipe in Suid-Afrika - : navorsings- en oorsigartikel

Volume 28, Issue 1
  • ISSN : 0254-3486
  • E-ISSN: 2222-4173


Die genus sluit van die kleinste mosselspesies in, kan bykans alle varswaterhabitats benut, is bodembewoners en fi ltervoeders en beskik oor 'n relatief lang lewensduur - eienskappe wat bydra tot hul geskiktheid vir die monitering van omgewingstoestande. Hierdie artikel fokus op die geografiese verspreiding en habitats van , 'n spesie wat tot Suid-Afrika beperk is en die omvangrykste geografiese verspreiding het van die ses -spesies wat in die databasis van die Nasionale Varswaterslakversameling (NVWSV) opgeneem is. Meer as 60% van die 428 monsters op rekord, is in spruite en riviere versamel en in watertoestande wat as standhoudend, staande, helder en vars beskryf is. Resultate dui daarop dat waterliggaamtipes, temperatuur en hoogte bo seevlak die belangrikste rol gespeel het in die daarstelling van die geografiese verspreiding van hierdie spesie. Landswye versameling van varswater Mollusca deur staatsinstansies is in die vroeë 1980's getermineer en die meerderheid vindplekke is sedertdien nie weer besoek nie. Dit bring mee dat hul gedokumenteerde verspreiding gevolglik verouder is en dat min oor hul bewaringstatus in Suid-Afrika bekend is. Omdat koeler klimaattoestande en standhoudende habitats verkies, kan verwag word dat klimaatverandering wat met aardverwarming gepaardgaan 'n negatiewe effek op die voortbestaan van die spesies mag hê. Pogings behoort aangewend te word om die geografiese verspreiding van minstens medies en veeartsenykundig belangrike spesies op te dateer en hul bewaringstatus te bepaal. Terselfdertyd sou die vordering van eksotiese indringerspesies in hul besetting van nuwe gebiede gemoniteer kon word.

Little is known of the functional role of freshwater bivalves and particularly the ecology of burrowing species has been inadequtely studied. This is an unfortunate situation in view of the fact that freshwater biotopes are losing biodiversity at an alarming rate. The genus includes some of the tiniest bivalve species known to man, it has a worldwide distribution and its origin is considered to be Mesozoic. Due to the fact that can exploit virtually almost any freshwater habitat, that it is a bottom dweller and filter feeder and is also relatively long lived, it is important to study species of this genus because they could be used for monitoring environmental conditions. This article focuses on the geographical distribution and habitats of , a species considered to be endemic to South Africa and which is the most widespread of the six species on record for this country in the database of the National Freshwater Snail Collection (NFSC).
Details pertaining to the habitats of the 428 samples of as recorded at the time of collection were extracted from the database of the NFSC. The 187 loci (1/16 th square degrees) in which the 428 collection sites were located, were distributed in pre-selected intervals of mean annual air temperature and rainfall, as well as intervals of mean altitude, to illustrate the frequency of occurrence within specific intervals. A temperature index was calculated for all mollusc species in the database from their frequencies of occurrence within the selected intervals and the results used to rank them in order of their association with low to high climatic temperatures. To evaluate the significance of the difference between frequencies of occurrence in, on, or at the various options for each parameter investigated, chi-square values were calculated. In addition an effect size value was calculated to determine the contribution of each parameter towards establishing the geographical distribution of this species based on the data in the database. A multivariate analysis in the form of a decision tree was also constructed from the data which enabled the selection and ranking of those variables that maximally discriminated between the frequency of occurrence of in, on, or at the various options for each parameter as compared to all other bivalve species in the database.
Our records show that this species is well represented in Gauteng and the central and southern areas of Mpumalanga. It is relatively continuously spread through the north eastern parts of the Free State and all along its eastern and southern borders, sparsely distributed in the Northern Cape and poorly represented in Limpopo.
Although it was reported from 13 of the 14 water-bodies represented in the database, more than 60% of the samples were recovered from streams and rivers and from water conditions described as perennial, standing, clear and fresh and more than 45% came from habitats with a predominantly muddy substratum.
From the effect size values calculated for the various parameters it can be deduced that type of water-body, temperature and altitude played the most significant role in establishing the geographical distribution of this species in South Africa.
On account of the fact that country-wide surveys by government and local health authorities were discontinued in the early 1980's the current range of the geographical distribution of freshwater mollusc species in South Africa is rather uncertain. The data in the database were compiled over a period of approximately five decades and due to the fact that the majority of sampling sites have not been revisited since, little is known of the conservation status of the freshwater molluscs of South Africa. Its close association with cooler climatic conditions as indicated by its temperature index and its dependency on perennial habitats, suggest that could be vulnerable to climatic changes due to global warming and that this could have a negative impact on the range of its geographical distribution. It is suggested that efforts should be made to update the geographical distribution of at least those mollusc species that are of medical and veterinary importance and at the same time to monitor the progress of exotic mollusc species in their invasion of water-bodies in this country. A comparison of the results of such surveys with the long range of data in the NFSC database could be valuable to assess the current conservation status of at least some of the indigenous freshwater molluscs of this country.

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