Nitrogen nutrition in assemblages dominated by Pseudo-nitzschia spp., Alexandrium catenella and Dinophysis acuminata off the west coast of South Africa

A study was carried out in the southern Benguela upwelling system in 2006 and 2007 to establish how the nutrient regime determines community succession and the selection of harmful algal bloom species. In March 2006, Pseudo-nitzschia spp. reached concentrations of 13 x 10 super(6) cells l super(-1), representing 80% of the total estimated phytoplankton biomass, while chlorophyll a (chl a) reached 57 kg l super(-1). High rates of NO sub(3) super(-) uptake (rho sub(NO) sub(3) sub(-), maximum 0.56 kmol N l super(-1) h super(-1)) led to NO sub(3) super(-) depletion (