Distribution of freshwater ostracoda (Crustacea) collected from wells of Benin: a preliminary study

Abstract

Context: Ostracods are small bivalved crustaceans that abound in almost all water bodies, marine and non-marine (including estuarine), surface waters both permanent and temporary and groundwater. They can be used as environmental tracers in several research domains through their response to different environmental conditions and anthropogenic impacts. Objective: The present research aims to study the distribution of freshwater ostracods from wells across the catchment areas of Benin. Material and methods: From 2015 to 2021, nearly 200 wells were sampled in four catchment areas using two sampling methods: the use of a phreatobiological net (100-150 µm) and the installation of baited traps. Sorted from all samples in the laboratory using a binocular microscope, ostracods were identified using existing literature. Identification of some taxa required complete dissections with valve morphology illustrated by scanning electron microscopy and limbs drawn under a microscope equipped with a lucid camera. Results: Thanks to the ecotone aspect of the sampled wells, the ostracod species are represented by two families: the Cyprididae collected in 70% of the sampled stations on the one hand and the Candonidae in 11% on the other. The Cyprididae, with about fifteen species, belong to several different biogeographic categories: circumtropical, afrotropical and endemic to West Africa and represent all surface dwelling and mostly well-described taxa. Despite the relative rarity of groundwater-dwelling Candonidae, they represented by more than twenty-five potentially new species. This reveals an exceptional diversity with a very high rate of endemism: each well harbors its own species and some wells contain up to three distinct species. This is the first time such a vast radiation of subterranean ostracods is reported from (West) Africa. Keywords: Distribution, ostracods, wells, biogeographic categories, endemism.