Characterization of phytoplankton assemblages in a tropical coastal environment using Kohonen self‐organizing map

Abstract

This study was aimed at understanding the main abiotic environmental factors controlling the distribution patterns of abundance and composition of phytoplankton (size less than 10 μm) assemblages in the coastal waters of south‐eastern Côte d'Ivoire. Data were collected during two cruises, in January (low‐water period) and October (high‐water period) of 2014. A total of 67 species were identified and assigned to Bacillariophyceae (49%), Cyanophyceae (21%), Chlorophyceae (13%), Euglenophyceae (10%), Dinophyceae (4%) and Chrysophyceae (3%). Three biotic zones (I, IIA and IIB) were distinguishable on a Kohonen self‐organizing map after an unsupervised learning process. The diatom genera Eunotia sp., Navicula sp. and Actinoptychus senarius are significantly associated with I, IIA and IIB biotic zones, respectively. A clear seasonal cum salinity trend was apparent in phytoplankton distribution patterns. Turbidity and nitrate levels were the main abiotic factors controlling phytoplankton distribution in I, the upland tidal regions of the lagoon. In regions along the lagoon–sea continuum, phosphate and turbidity exert the most control during the low‐water season (IIA), while total dissolved solids control phytoplankton distribution during the high‐water season (IIB). These are climate‐sensitive parameters whose concentrations depend on prevailing hydroclimatic processes. Therefore, seasonality can have important consequences on phytoplankton community and inadvertently the productivity of these systems.

The Role of Macrophytes in Biogenic Silica Storage in Ivory Coast Lagoons

“…Because diatoms are primary producers at the base of the food-web, any change in that production might have knock-on effects to the entire ecosystem. Phytoplankton assemblages at Ivory Coast coastal environment show that, although diatoms are the most species-rich, cyanobacteria are the most abundant (up to 90% of the phytoplankton biomass), and silica was identified as predominant abiotic factor controlling phytoplankton dynamics (Osemwegie et al, 2016). Expected human population rise in the greater Abidjan area however, will probably put more pressure on local water bodies and nutrient levels may increase to levels which could escalate to dramatic levels of eutrophication [projections made for the nearby (and larger) Ebrié Lagoon which receives water from the Comoé River; (Scheeren et al, 2004)].…”