Spatiotemporal distribution of zooplankton in relation to some abiotic variables in the waters of the Kribian Atlantic coast (South Cameroon)

Abstract

A research to study the zooplanktonic population in relation to some abiotic variables of the Kribian coast waters was conducted from July to December 2020 following a monthly sampling in six (6) selected sites. The physicochemical parameters were determining out using standard methods. Concerning the zooplankton, the water was collected at the surface, in the trophogenic and tropholytic layers, then filtered through a 64 µm plankton sieve and the retentate was fixed with 96% alcohol. Identification and counting were done in the laboratory using a Wild M5 binocular loupe, appropriate keys and works. The physicochemical results showed a very good oxygenation of the waters (91.85 ± 3.87%), basic pH (8.43 ± 0.54 U.C), a low salinity and conductivity of respectively 13.04 ± 3.92 g/L and 23.07±4.23 µS/cm characteristic of the haline domains and a temperature of 28.66 ± 1.35°C. With regard to nutrients, the values recorded showed a progressive enrichment of the water in nitrate (2.2±1.81mg/L) and a low concentration in orthophosphate (0.25±0.41mg/L). the zooplankton community haboured, 54 taxa belonging to 3 major groups (Copepoda, Cladocera, Ciliate) and other Zooplankton, 24 families and 29 genera were recorded. The Copepod group dominated the taxonomic richness with 34 taxa (62.96% of total richness), followed by Tintinidae with 4 taxa (7.4%), Cladocera with 1 marine taxa (1.9%) and 15 taxa for other zooplankton (27.8%). Quantitatively, Copepods were once again the most abundant group in the population, with an average of 78.3% of the total zooplankton abundance. The dominant copepod taxa in terms of abundance were those of the families of: Paracalanidae (mean abundance: 116 ind/L) and Oithonidae (mean abundance: 99ind/L).