Influence of some environmental variables on the diversity and distribution of aquatic oligochaetes (Clitellata: Annelida) in the Nyong estuary (Atlantic coast, southern Cameroon)

• 1016 individuals grouped into 3 orders (Tubificida, Haplotaxida and Lumbriculida), 5 families (Naididae, Tubificidae, Haplotaxidae, Glossoscolecidae and Lumbriculidae) and 5 species were collected and identified. • Alma nilotica , positively correlated with dissolved oxygen (P < 0.05), was the most abundant species (464 individuals), followed by Tubifex tubifex (224 individuals), positively correlated with salinity, pH and temperature (P < 0.05). • Limnodrilus hoffmeisteri and Rhynchemis sp. showed no particular affinity with the abiotic component considered in this study. • Shannon-Weaver (H') and Pielou's evenness (J) indices coupled with the species richness of stations S1 to S12 showed a greater diversity of taxa only at station S12 during the dry season. Tropical estuarine ecosystems are subject to strong anthropogenic pressures, with the direct consequence of declining or lost biodiversity. An essential and little-known biological component of these estuarine ecosystems is the population of oligochaete annelids, which play an indispensable role in energy transfer and the biodegradation of organic and chemical compounds. This study sheds light on the diversity and structure of oligochaetes in the Nyong estuary under the influence of some abiotic parameters. Based on hydrobiological standard techniques, 1016 individuals grouped into 3 orders (Tubificida, Haplotaxida and Lumbriculida), 5 families (Naididae, Tubificidae, Haplotaxidae, Glossoscolecidae and Lumbriculidae) and 5 species were collected and identified. Alma nilotica , positively correlated with dissolved oxygen ( P = 0.033; n = 72), was the most abundant species (464 individuals), followed by Tubifex tubifex (216 individuals), positively correlated with salinity ( P = 0.029; n = 72), pH ( P = 0.037; n = 72) and temperature ( P = 0.044; n = 72) Limnodrilus hoffmeisteri and Rhynchemis sp. showed no particular affinity with the abiotic component considered in this study. The Shannon-Weaver's (H') and Pielou's evenness (J) indices coupled with the species richness of all surveyed stations (S1 to S12) showed a greater diversity of taxa only at station S12, located in the lower estuary, 1 km from the mouth; during the dry season. This study shows that the spatial dynamics of oligochaetes in the Nyong estuary are strongly influenced by abiotic parameters and seasonal cycles.