Distribution of Alexandrium fundyense and A. pacificum (Dinophyceae) in the Yellow Sea and Bohai Sea

•A fundyense and A. pacificum are important HAB-forming dinoflagellates in China.•Distribution of A. fundyense and A. pacificum was studied with qPCR based assays.•Two species formed spatially distinct populations in Yellow Sea and Bohai Sea.•The results offered a sound basis for specific monitoring of toxic Alexandrium spp. This study characterizes the distribution of two closely related, causative species of paralytic shellfish poisoning – Alexandrium fundyense and A. pacificum – within the Yellow Sea (YS) and Bohai Sea (BS). These two Alexandrium species are distinguished for the first time in a regional field study using species-specific, quantitative PCR (qPCR) based assays. Both qPCR assays target the large subunit ribosomal DNA gene and were used to analyze net-concentrated phytoplankton samples collected in May 2012. A. fundyense was mainly distributed in YS, while A. pacificum was confined to an area adjacent to the Changjiang River estuary. The different distribution of the two species is interpreted as evidence of their distinct bloom ecology. Expanded efforts implementing these assays offer the ability to discriminate the dynamics of A. fundyense and A. pacificum blooms and provide a more sound basis for monitoring toxic Alexandrium species in this region.