Biodiversité des macroinvertébrés benthiques des cours d’eau côtiers dans la zone de Kribi (région du Sud Cameroun)

Abstract

The study took place in the Department of Ocean, Southern Cameroon region from January 2022 to February 2023. Eight (08) rivers have been selected and divided into 24 sampling stations. The objective of our study was to study the biodiversity of benthic macroinvertebrates in the coastal zone in the Southern Cameroon region. Hydrological, particle size and physicochemical analyses were carried out using conventional methods. Sampling of benthic macroinvertebrates was carried out using the multihabitat approach, the organisms were then counted and identified under a binocular magnifying glass using the appropriate identification keys and books. The results of the hydrological and particle size analyses show variations in the sediment composition and structuring, indicating a heterogeneous distribution of the substrate. The physicochemical quality of the water reveals that the temperature (25.3 27.28 °C), turbidity (0-55.53 NTU), electrical conductivity (21.33-262 μS/cm), suspended solids (0-34.69 mg/L), dissolved oxygen (47.83-79.11%), ammoniacal nitrogen (0-1.96 mg/L), nitrate ions (0-1.09 mg/L) and nitrite ions (0-0.99 mg/L), orthophosphates (0-12.48 mg/L) and pH (6-9.8 CU) are in the range of moderate ecological quality. This is in agreement with the Organic Pollution Index (IPO) which indicates a moderate level of pollution in all waterways. During this study, 17055 benthic macroinvertebrate individuals were collected with a total of 116 taxa identified at the rank of genus and/or species. These taxa have been divided into 2 phyla (Arthropods and Molluscs), 3 Classes (Gastropods, Crustaceans and Insects), 19 Orders, and 59 Families. The class of Gastropods is the most abundant with 7593 individuals, i.e. 44.52% relative abundance. It is followed by the Class of Crustaceans which totals 7139 individuals or 41.86% relative abundance. Finally, comes the class of Insects which has 2323 individuals for 13.62% relative abundance. As for the Orders, the Decapods are the most represented with 7139 individuals, i.e. 41.86% relative abundance. This supremacy of the Decapods reflects the little anthropized nature of the watercourses studied. The Shannon & Weaver Diversity Index, the Piélou Equitability Index and the Simpson Index reveal a rich, diverse benthic macroinvertebrate population that is equitably distributed throughout the rivers. The biological characterization carried out from the Principal Component Analysis (PCA) and the Hierarchical Classification Analysis (ACH) shows that the 24 stations are grouped on the basis of their organisms into three groups. Group I is made up of stations located near the Atlantic Ocean, Group II is made up of stations located in forest areas and Group III is made up of stations located in peri-urban areas. Multiple Correspondence Analysis (MCA) has highlighted the particle size, physicochemical and biological parameters. The IndVal method identified 73 significant indicator benthic macroinvertebrate species, four of which have IndVal XVII values ⩾ 75% and B⩾ 60% fidelity values. These can be considered as the best indicators of the conditions prevailing in these different coastal rivers. These include Caridina africana, Caridina nilotica, Macrobrachium macrobrachiom and Macrobrachium nilotica belonging to the order Decapodae.