Distributional Patterns of Gastropoda Upstream and Downstream of Bujagali Hydropower Project along the Upper Victoria Nile

Abstract

Abstract. To better understand the gastropod community dynamics of fresh water snails in the Upper
Victoria Nile (UVN), the spatial and temporal abundance changes in gastropod assemblage were
assessed biannually from April 2006 to April 2021 at three transects. Biannual abundances of
gastropoda were obtained by a ponar grab to examine changes in their community structure in relation
to Bujagali Hydropower Project (BHP). The gastropod community consisted of nine species
belonging to five families (Thiaridae, Viviparidae, Ampullariidae, Bithyniidae and Planorbidae).
Pulmonate species registered five species (Anisus natalensis, Gyraulus sp., Segmentorbis sp., Bulinus
sp. and Biomphalaria chaonomphola). Two of the pulmonates (Bulinus sp. and B. chaonomphala)
are schistomiasis vectors. The pulmonates (A. natalensis, Gyraulus sp., Segmentorbis sp.) were rare
and intermittently occurred with abundances up to 47 ind.m-2
. Four prosobranch species (Gabbia
humerosa, Pila ovata, Melanoides tuberculata and Bellamya unicolor) were encountered. Of these
prosobranchs, P. ovata was the rarest while M. tuberculata and B. unicolor were the commonest. The
gastropod community in the UVN was characterised by prosobranchs-dominated abundance which
over the 16-year monitoring period often registered peak densities of > 1000 ind.m2
. The inter-site
Percent Similarity Index (PSI) (94-100%) indicated a high degree of similarity of gastropod
community across the sites.