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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.

The Douala harbour represents the main gateway through which human activities introduce invasive ants, so that Solenopsis geminata (Fabricius, 1804) originating from Neotropics has been reported in several areas of the Littoral region of Cameroon. But nothing is known about the ant community structure and composition of the coastal zone. We hypothesized that environmental perturbations around Douala have repercussions on the native litter-dwelling ants. Collections conducted in 33 houses, six gardens of 225 m² each, 41 plantations of one hectare each and 34 two-year old fallows of one hectare each suggested lowly even communities, low species richness, low diversity and low dominance by a few species. Among 28 species recorded four species were mostly represented: two foreign origin species [S. geminata (Fabricius, 1804) and Trichomyrmex destructor (Jerdon, 1851), from tropical America and India respectively], one native species [Pheidole megacephala (Fabricius, 1793)] and two ambiguous native range species [Paratrechina longicornis (Latreille, 1802) and Tapinoma melanocephalum (Fabricius, 1793)] since they have long been recorded as having a widespread distribution. Alien species were highly represented than native ones (52.9% and 47.1% respectively, p<0.001). Inside houses, gardens and plantations the ant species were distributed according to the geometrical progression (Motomura’s model) while in the old fallows abundance distribution suggested an evolved ecosystem (Mandelbrot’s model). Between the three dominant species [Pa. longicornis (Latreille, 1802), Ph. megacephala (Fabricius) and S. geminata (Fabricius)], the first species was positively correlated with the third one while other associations were not significant. These dominant species appeared influencing the abundance of the rare species. Dominance and high abundance of a few species indicated that areas were influenced mostly by interspecies competition and/or disturbance by human activities.