Assessment of benthic molluscs diversity and distribution in urban reservoirs (Ouagadougou, Burkina Faso)

Abstract

The urban reservoirs n° 2 and n°3 of Ouagadougou, located in the middle of the city are subject to multiple anthropogenic pressures which threaten the diversity of benthic macroinvertebrates community group like molluscs. This study was initiated to assess the diversity and distribution of benthic molluscs in these reservoirs. Molluscs samples were collected monthly using an Eckman grab (12 x 20 cm²) between September 2011 and February 2012 in 24 sampling points defined on each reservoir. In parallel, physicochemical variables and water colon depth were measured. After sampling, molluscs were transported to the laboratory for identification. A total of 328 specimens were collected of which 5 species were identified: three species of Gastropods (Bellamya unicolor, Cleopatra bulimoïdes, Lanistes ovum) and two species of Bivalves (Coelatura aegyptiaca, Mutela rostrata). B. unicolor was the most abundant species with 71% of the collected molluscs and preferentially occupied the edges of the reservoir. It was followed by C. aegyptiaca (27%) which was abundant in the central axis of the reservoir. Physicochemical variables influence the distribution of species. For all measured physicochemical factors, B. unicolor was more tolerant than C. aegyptiaca on the occupation of available habitat.

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Keywords: Bivalves, Gastropods, available habitat, physicochemical variables, anthropogenic pressures