Copepod nauplii abundance variation and influence of environmental variables on their development in the waters of the Upper Bandama (Côte d’Ivoire)
The aim of this study is to investigate spatial and temporal variations of copepod nauplii abundance in relation to environmental factors. To this end, water and zooplankton sampling was conducted from November 2017 to September 2018 in the Lokpoho River (tributary of the Bandama River) and in the main stem of the Bandama River. The analyses of the samples showed that copepod nauplii are more abundant in the dry season (mean 74 ind∙L-1) than in the rainy season (mean 51 ind∙L-1), with the highest values recorded in the middle of the dry season (118 ind∙L-1). The average annual abundance of nauplii in the Lokpoho River (77 ind∙L-1) is higher than in the Bandama River (38 ind∙L-1). During the dry season, nauplii abundance is strongly influenced by conductivity, dissolved oxygen and pH. During the rainy season, the main variables influencing nauplii abundance are manganese, transparency, chlorophyll a and nitrate. Annually, the abundance of copepod nauplii is positively and significantly influenced by the abundance of adult copepods and transparency. However, nitrate levels have a negative influence on the development of copepod nauplii in the Upper Bandama. This negative influence is thought to be due to agro-pastoral activities in the Ferké region.