Benthic Fauna Assessment along the Navigation Channel from the Mouth of the Casamance Estuary to Ziguinchor City

Abstract

This study aimed at studying the benthic fauna of the Casamance estuary (Senegal) through the analysis of its composition at 13 stations located along the channel from the estuary mouth to Ziguinchor port (estuary upstream), which may provide indications of the potential environmental impact of the navigation channel dredged on the estuary. Sixty taxa distributed in twelve phyla were identified, of which the most abundant were bivalve mollusks, annelids, and nematodes. The species abundance and species richness varied from five (estuary mouth) to thirty species (upstream). Correspondence factorial analysis (CFA) and factor analysis for mixed data (FAMD) showed, respectively, that 34% (Dim 1 = 15.6% and Dim 2 = 18.4%) and 35.5% (Dim 1 = 20.8% and Dim 2 = 14.7%) of total inertia was explained by the first two axes and a significant correlation between the dominant species distribution, sediment type, and depth of the sampled station. Overall, Spearman’s rank correlation indicated a significant negative correlation of the species abundance and species richness with distance from the estuary mouth. From these results, it appears that sediment type, depth of the sampled stations, salinity, and the mangrove forests are key factors that influence the distribution and abundance of benthic fauna in the Casamance estuary. The monitoring plans for the preservation of the health and biological diversity of this ecosystem, especially benthic fauna biodiversity, should take into consideration the seasonal variations of rainfalls and related changes in terms of physicochemical factors. This should include evaluating the long-term responses of benthic organisms to dredging activities, boat traffic, and especially physical habitat modifications, changes in migration ways, and pollution pressure.