Morphology and toxicity of Pseudo-nitzschia species in the northern Benguela Upwelling System.

•Distribution, diversity and ultrastructure of Pseudo-nitzschia in nBUS (2004–2011).•16 Pseudo-nitzschia species, nine toxin producers and one new species documented.•Toxigenic P. pungens and P. australis were dominant species inshore.•During a warming event, a community shifted to P. fraudulenta and P. multiseries.•A toxic event in August 2004 revealed the presence of P. australis and P. pungens.