Distribution and habitats of Burnupia trapezoidea (Boettger, 1910) (Gastropoda: Ancylidae) in South Africa

Abstract

This paper deals with the geographical distribution and habitat preferences of B. trapezoidea, the third most widespread species of the 14 species of Burnupia currently on record in the database of the National Freshwater Snail Collection (NFSC) of South Africa. Although the 121 loci (¹/₁₆ square degrees) from which the 445 samples of B. trapezoidea were collected are much fewer than the number reported for B. capensis, the range of its geographical distribution is almost as widespread as that of B. capensis. The limited distribution of B. trapezoidea in the Limpopo, Northern Cape and Western Cape Provinces can most probably be attributed to the paucity of perennial water bodies in these areas and the fact that Burnupia spp. in general have poor abilities to overcome conditions of desiccation prevalent in these areas. It is therefore not surprising that the majority of samples were collected in perennial rivers and streams. A Random Forest statistical analysis selected water bodies, the presence or absence of marginal and aquatic vegetation, and type of substratum as the most important variables that played a significant role in determining the presence and numbers of specimens of B. trapezoidea in a specific area. In this respect, temperature and turbidity, respectively, played a moderate and minor role. Little is known regarding the conservation status of Burnupia spp, in general, but habitat degradation and climatic warming could be reasons for concern. However, in extensive on-going biodiversity surveys in two rivers and selected tributaries in the North-West Province, many new distribution records of B. trapezoidea are still being created and therefore this species could probably be considered for listing as not endangered. In view of its wide distribution, largely sessile, benthic lifestyle, and ability to bioaccumulate various substances, the feasibility to utilise it as indicator of river ecosystem health in South Africa should be explored.

Keywords: Mollusca, Ancylidae, Burnupia trapezoidea, geographical distribution, habitat preferences, conservation status, South Africa