Differential spatial–temporal dynamics of Alexandrium species revealed using metabarcoding analysis by the 18S rDNA V4 region in Jiaozhou Bay, China

The dinoflagellate genus Alexandrium hosts many toxigenic species with remarkable negative influence on ecosystems and human health by developing harmful algal blooms (HABs). Despite 34 Alexandrium species having been characterized with unique taxonomical features, relatively few Alexandrium species have been identified and traced in ecological studies, largely due to the limited resolution of morphology-based methodologies and demanding workload associated with ecological studies. Thus, both diversity and spatial–temporal dynamics of Alexandrium species in marine ecosystems remain poorly resolved and understood, leading to severe under appreciation of Alexandrium species in ecosystems. In this project, metabarcoding of the 18S rDNA V4 region was applied for the first time to quantitatively ascertain biodiversity and spatial–temporal dynamics of Alexandrium species in Jiaozhou Bay, a semi-enclosed model ecosystem in Qingdao, China. Eight known Alexandrium species ( A. affine , A. andersonii , A. catenella , A. leei , A. minutum , A. ostenfeldii , A. pacificum , and A. pohangense ), one unidentified Alexandrium species, and possibly three additional Alexandrium species ( A. hiranoi , A. pseudogonyaulax , A. insuetum ) were successfully identified in this study, compared to only four previously reported Alexandrium species in Jiaozhou Bay, demonstrating the competitive strength of metabarcoding technology in ecological research of Alexandrium species. Quantitative analysis showed that most Alexandrium species displayed strong temporal dynamics with high abundance in months with relative high temperature. In particular, Alexandrium affine displayed a strong preference from June to December, peaking in September, suggesting that temperature is an important driving factor for the temporal dynamics of Alexandrium species. However, Alexandrium catenella displayed preference from January to May. Metabarcoding analysis could be widely applied for detection and study of spatial–temporal dynamics of Alexandrium species.