Available online at http://www.ifg-dg.org Int. J. Biol. Chem. Sci. 9(4): 2066-2077, August 2015 ISSN 1997-342X (Online), ISSN 1991-8631 (Print) Original Paper http://ajol.info/index.php/ijbcs http://indexmedicus.afro.who.int Assessment of benthic molluscs diversity and distribution in urban reservoirs (Ouagadougou, Burkina Faso) Idrissa OUEDRAOGO *, Adama OUEDA, Djidama SIRIMA, Ilassa OUEDRAOGO, Wendengoudi GUENDA and Gustave B. KABRE Laboratoire de Biologie et Ecologie Animales, UFR-Sciences de la Vie et de la Terre, Université de Ouagadougou 03 BP 7021 Ouagadougou 03, Burkina Faso. *Corresponding author, E-mail: [email protected]; Tel.: 00226 70 99 05 74 ACKNOWLEDGEMENTS This study was funded by CIOSPB (Centre d’Information de l’Orientation Scolaire, Professionnelle et des Bourses) and the SUSFISH Project (Sustainable management of fisheries and aquatic resources). We are grateful to them. 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 cm 2) 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. © 2015 International Formulae Group. All rights reserved. Keywords : Bivalves, Gastropods, available habitat, physicochemical variables, anthropogenic pressures. INTRODUCTION majority of these reservoirs were created in Burkina Faso, a sahelian country the Nakanbé River catchment where the located in West Africa, does not enjoy much population density is high, particularly in and surface water and this lead to the around the city of Ouagadougou. These implementation of a surface water control reservoirs contribute to the local development policy by building many dams throughout the by providing fisheries (Ouéda et al., 2008), country (Ouéda et al ., 2007). The large drinking water, water for agriculture (Kpoda © 2015 International Formulae Group. All rights reserved. DOI : http://dx.doi.org/10.4314/ijbcs.v9i4.29 I. OUEDRAOGO et al. / Int. J. Biol. Chem. Sci. 9(4): 2066-2077, 2015 et al., 2015) and the preservation of is around 88 ha with a capacity of 3 733 334 biodiversity. But despite their importance, m3. The depth of the dykes is about 288.67 m. most of these reservoirs do not have sufficient Reservoir n° 2 is situated upstream the attention and are gradually degrading due to reservoir n° 3, and water can flow from the pressure imposed by human activities. As reservoir n°2 to the reservoir n°3 throughout consequence, this water from some reservoirs 60 rectangular opening (1.20 x 0.5 m) situated (eg. Reservoir 2 and 3 of Ouagadougou) under the dyke of the reservoir n° 2 (Gueye, shows higher concentrations of sulphates, 2004). Created in 1963, these reservoirs are nitrates and also heavy metals (mercury, total actually impacted by diverse activities, selenium dissolved and total dissolved including vegetable gardening (that use arsenic) (Ouédraogo and Aymot, 2013). prohibited chemicals fertilizers and Aquatic organisms are sensitive to such pesticides); fisheries activities; car washing disturbances that can lead to species and regular water withdrawals. Another disappearance. Zheng et al. (2015) has remarkable impact is the discharge of showed that for Zn, Pb, Cr, Cd, Hg, and Cu, wastewater and solid wastes directly into the invertebrates exhibited higher sensitivity than reservoirs from the neighbouring houses. vertebrates. Among these organisms, benthic By means of Garmin GPS 76, 6 molluscs are particularly vulnerable because transects, each with 4 sampling points, were of their limited ability to move and thus to defined on each reservoir. Then, twenty four escape pollution. Because of this sampling points were visited each month vulnerability, it is important to assess the during the dry season (from September 2011 diversity of this group in these two reservoirs. to February 2012) in each reservoir. In Burkina Faso, most studies on molluscs have focused only on the distribution Environmental variables of the intermediate hosts of schistosomes The stations were characterized by (Poda et al., 2004). However, although some using 4 physicochemical variables and depth. are parasites vectors, molluscs play important Physicochemical variables measured are: functions in aquatic ecosystems (El-Wakeil et temperature, conductivity, pH and al., 2013), especially in food chain (Odler et transparency. Apart from the transparency al., 2013), in bioindication (Payet and Obura, which has been measured with a Secchi disk, 2004; Younger and Reese, 2013) and the other physicochemical variables were bioaccumulation (Fang et al., 2001; Usero et measured with a multiparameter HANNA. al., 2005). The depth of the water column was measured The objective of this study was to with a ballasted tri -decameter. highlight the diversity of benthic molluscs in these reservoirs and analyse their distribution Molluscs sampling in relation to some physicochemical variables. Molluscs was sampled aboard a canoe with an Eckman grab (sampling surface = MATERIALS AND METHODS 0.024 m 2). In each reservoir, one sample unit Study area was taken from each of the 24 sampling point. Our study sites, reservoirs n°2 and n°3 After the grab raised, its content was spilled of Ouagadougou, are located in the central on a sieve (mesh size 0.8 mm) and washed to part of the town between longitudes remove the mud. Living specimens and empty 01°30'03.79’’W and 01°33'17.48’’W and shell found were sorted and preserved in latitudes 12°23’03,79’’N and 12°23’36,04’’N. alcohol (70° final concentration). In the The reservoir n°2’s surface is 226 ha with a laboratory, molluscs specimens were capacity of 2.33 million m 3. The dyke’s depth determined using Mandahl-Barth (1978) and is around 288.3 m. The reservoir n°3’s surface Leveque (1980) identifications keys. 2067 I. OUEDRAOGO et al. / Int. J. Biol. Chem. Sci. 9(4): 2066-2077, 2015 Data analysis Species diversity All the analyses were performed with Table 1 shows the taxonomic the R.3.1.1 software (R Development Core composition of Molluscs community in the Team, 2014) in RStudio (Version 0.98.1049) two reservoirs. Five species belonging to five interface. Statistical tests were performed families and two classes (Gastropoda and using the stats package. The Shapiro-Wilk test Bivalves) were identified. Thus, each family was first performed to check the normality of is represented by a single species. The class of physicochemical variables distributions. As all Gastropoda is composed by Bellamya variables are not normaly distributed, we used unicolor Olivier, 1804; Cleopatra bulimoïdes the Mann Whitney-Wilcoxon test to check (Olivier, 1804), and Lanistes ovum Peters, variability of physicochemical variables 1854. Bivalves are composed by Coelatura according to reservoirs and also to test the aegyptiaca (Cailliaud, 1827) and Mutela difference between available habitat and those rostrata (Rank, 1835). The living specimens used by species. This test was considered found belong to Bellamya unicolor and significant for p <0.05. Coelatura aegyptiaca . Cleopatra bulimoïdes Rarefaction curve (Magurran, 2004) and Mutela rostrata were mentioned on the was used to estimate molluscs species basis of empty shells. Lanistes ovum was richness in the two reservoirs. It is observed in a sample from the reservoir n°2 accompanied by Chao index which gives an and collected outside the method used for this estimation of the maximum richness expected study. in the area. Rarefaction curve was graphed Rarefaction curve gives no horizontal based on the matrix of species using the vegan tangent (Figure 3). This means that the and BiodiversityR packages (Kindt and Coe, probability to find new species exists if other 2005). samplings are conducted. Indeed, the Chao To analyse spatial distribution, only the test foresees a total of 8 species in these most abundant and species found alive in the reservoirs. So we can hypothesize that three reservoir n° 3 were considered. First, a map of more species are susceptible to be found in the reservoirs shape and sampling points was these reservoirs. created with the adehabitat (Calenge, 2006) and lattice (Sarkar, 2008) packages using Species abundance geographical coordinates recorded with a GPS The relative abundance of benthic (Figure 1). Abundance of species at each molluscs, considering living specimens and sampling point were then projected. empty shell in reservoirs n°2 and n°3 of Ouagadougou is presented in Figure 4. B. RESULTS unicolor is the most abundant with 71% of Physicochemical characteristics of collected specimens. It is followed by reservoirs Coelatura aegyptiaca (27%) and Cleopatra Figure 2 (A-D) shows the variation of bulimoïdes with (2%). M. rostrata represents physicochemical variables in the two less than 1% of specimens. Figure 5 compares reservoirs. The median values of transparency, the abundance of empty shells to living temperature and depth are highest in the molluscs for each species. For all species, reservoir n°3 than reservoir n°2. The average empty shells are more abundant than living values of pH and conductivity are highest in specimens.