Phytoplankton assemblages and pigments in the exclusive economic zone of Mauritius (Indian Ocean)

Abstract

Nutrient enrichment studies showed that both inorganic salts of nitrogen and phosphorus were limiting for phytoplankton from the surface waters. This coupled with conditions of high insolation prevailing at this time (Sept.-Oct.), severely curtailed phytoplankton growth in the surface waters leading to formation of a distinct subsurface chlorophyll maximum (SCM). In the vicinity of Agalega islands, the enhancement of phytoplankton biomass was associated with an upwelling process caused by the confluence of the westward flowing branch of the South Equatorial Current with the Seychelles-Mauritius Ridge. The inadequacy of processes such as vertical diffusion and nutrient regeneration in sustaining phytoplankton in surface waters highlights the importance of current-driven upwelling in transporting nutrients to the surface waters of the euphotic column within this region.