Species composition and diversity of freshwater snails and land snails at the swampy areas and streams edges in the urban zone of Douala, Cameroon

Abstract

Fascioliasis and bilharzia occur in the Littoral region of Cameroon. Recent reports indicate a high prevalence of bilharzia in school-age children in the locality of Njombé-Penja, close to the city of Douala. This infectious disease may spread in the near future to the city of Douala, especially if the localities at risk are visited by infected people, who defecate or urinate in streams or swamps as is the habit of populations in populous zones of the city and where environmental cleanliness is not respected. It is known that several molluscs are intermediate hosts of the infectious agents of this pathology but little is known about the snail’s community structure at the coastal zone of the country. The present study aimed to establish a baseline of information on the distribution of snails in the urban environments of the Douala coastal Littoral-zone, as a first step in evaluating the status and the occurrence level of snails known as intermediate hosts of schistosomiasis and distomatosis agents. Seventy-three sample units where inspected from July to November 2020 in eight quarters of the Douala city, using 49 non-contiguous transects 5x40 m² each along streams and 24 non-contiguous quadrates 10x10 m² each around swamps. A total of 4,068 snail’s shelter belonged to 9 families: 3(33.3%) and 6 (66.7%) families for land and freshwater snails respectively. Specimens belonged to 14 genera [6 (42.9%) and 8 (57.1%) genera for land and freshwater snails respectively], and 30 species [14 (46.7%) and 16 (53.3%) species for land and freshwater snails respectively]. Land snails were most diverse [E(Sn=151) = 14 ± 0 species] than freshwater snails [E(Sn=151) = 11 ± 1 species]. Economically important species were highly represented in land snails (30.3%) and lowly represented in freshwater snails (6.1%). Between land snails Achatina and Archachatina (invasive pests for agriculture) were highly recorded in Bépanda-Sic-Cacao, Makepé-Missoké and PK10-Plateau quarters while between freshwater snails known as obligate intermediate hosts for fascioliasis and bilharzia agents, Lymnaea was recorded in Bépanda-Sic-Cacao, Nkomba and Mbanga-Pongo quarters while Biomphalaria occurred exclusively in PK10-Plateau quarter. The community exhibited low evenness, low species richness, low species diversity and low dominance by a few species. The theoretical lognormal model fitted the species abundance distributions and species exhibited a positive association (Schluter’s ratio VR = 6.69, statistic W = 53.49, df = 8, p<0.001 for land snails; VR = 2.27, W = 18.18, df = 8, p = 0.020 for freshwater snails; VR = 4.17, W = 33.42, p<0.001 for the pooled data). Low dominance by a few species indicated that study sites were slightly influenced by interspecific competition and/or disturbance by human activities.

Water Quality, Biodiversity and Abundance of Blue-Green Algae in Nyong and Kienké River Mouths (South-Cameroon)

“…Contrary to the lognormal model which describes the relationship between the logarithm of the abundance and the probit of the ranks of the species and which reflects a community where the majority of species shows moderate abundances, the log-linear model corresponds to a community in which a reduced number of dominants is recorded. Motomura niche partitioning model and/or lognormal model are reported fitting SADs of zooplankton along a salinity-temperature gradient from coastal neritic to estuarine conditions in the Arcachon Bay (France) [76], the freshwater snails' assemblage at the swampy areas and streams edges in Douala (Cameroon) [77]. Given that nomocenosis are associations of species subject to the influence of the same factors and whose species profile is sufficiently close to be assimilated to the log-linear or log-normal model, they seem to characterize the stands of disturbed environments with a strong competition between species for the exploitation of available resources.…”

Biodiversity and the Community Structure of Chromista Cavalier-Smith, 1981 in Nyong and Kienke River Mouths (South-Cameroon)

“…Pooled SAD fitted in the dry season, the ZM model with a low fractal dimension of the distribution of individuals among species ((1/γ)<1). LN model describes a community where the majority of species show moderate abundances and it is reported fitting SADs of zooplankton in coastal neritic and estuarine conditions in the Arcachon Bay (France) [70], the freshwater snails at swampy areas in Douala (Cameroon) [71], the Cyanobacteria in Nyong and Kienke [41]. Given that nomocenosis are associations of species subject to the influence of the same factors, they characterize evolved or less disturbed environments.…”