Diversity and dynamics of potentially harmful algal bloom species in the Qinhuangdao region revealed by high-frequency environmental DNA metabarcoding

The coastal region offshore Qinhuangdao in China has been known to develop harmful algal blooms (HABs) with high frequency and devastating negative impacts. However, due to technological limitations in species identification and infrequent sampling, the diversity and dynamics of HAB species in this ocean region remain poorly understood. To address these issues, this study conducted a metabarcoding analysis of yearlong weekly samples in the Qinhuangdao region from September 2022 to August 2023. Based on metabarcoding analysis of the molecular marker 18S rDNA V4 sequences, a total of 316 phytoplankton species were identified, belonging to 304 genera and 8 phyla, with Dinoflagellata being the most dominant represented phylum. Of these phytoplankton species, 67 potential HAB species were identified, including 21 species being identified for the first time in the Qinhuangdao region. Sixty-one phytoplankton species (including HAB species) identified in the Qinhuangdao region exhibited strong seasonal dynamics. Environmental factors (especially temperature) and interspecific interactions may be the main driving factors affecting the diversity and dynamics of HAB species. In conclusion, this study provides a detailed description of the species composition, temporal dynamics, environmental driving factors, and interspecific interactions of HAB species in the Qinhuangdao region. The high biodiversity of HAB species in the local coastal ecosystem indicates the need for long-term monitoring to further study and prevent potential HABs.