Taxonomic diversity of phytoplankton and trophic status of the waters

Introduction

Located in West Africa, Côte d'Ivoire has immense physical, hydrological (150.000 ha of lagoons, 350.000 ha of lakes and numerous lowlands, etc.), climatic and human potential, in addition to a rich aquatic fauna containing more than 100 families of fish, several species of which have definite aquaculture potential (FAO, 2015). Thus, coastal lagoons are complex socio-ecological systems that rank among the most biologically productive and important ecosystems on the Planet, providing goods and services valuable for human welfare (Kennish and Paerl, 2010; Newton et al., 2018). Among these lagoons, the Ebrié lagoon, with a surface area of 566 km2 , is one of the most important aquatic ecosystems due to its ecological values and its aquaculture operations. As part of the pilot projects for the development of lagoon aquaculture and fisheries in Côte d'Ivoire, the Ivorian government has initiated the creation of the Jacqueville aquaculture station. The station is located on the banks of sector V of the Ebrié lagoon. However, aquaculture can have an impact on water quality. Preservation and management of these environments requires knowledge of abiotic and biotic factors. Thus, the study of planktonic communities appears to be important for understanding the functioning of farming structures (Ndour et al., 2017). According to Anneville et al. 2019, plankton comprises several organisms, one of the most important of which is phytoplankton. That's right, phytoplankton are the main producers of aquatic ecosystems and can respond to environmental changes in a short period of time and are better indicators of environmental changes (Padisák et al., 2006). It also provides aquatic food webs with energy, high-quality biochemical compounds and minerals (Peltomaa et al., 2017). However, phytoplankton blooms have a direct impact on aquatic ecosystems, leading to changes in diversity and population dynamics (Groga, 2012). This makes this compartment a potential bioindicator of the quality of water bodies. In addition, temperature and nutrient increases have been shown to alter phytoplankton total biomass, community structure and the biochemical composition of individual Cells (Winder and Hunter, 2008; Taipale et al., 2019). Knowledge of phytoplankton diversity is essential for the preservation and efficient management of aquatic ecosystems. Different strategies can therefore be used to assess the limitation of phytoplankton by nutrients. In order to assess the trophic status of a body of water, it is therefore important to be able to monitor and assess the composition, abundance and biomass of phytoplankton communities, as well as their variability in space and time. This assessment can be made using biotic indices such as the planktonic index, the Carlson index and trophic status.

The aim of this study is to determine the composition and structure of phytoplankton in the waters of the Jacqueville aquaculture station in order to assess its trophic status.