High-throughput phytoplankton monitoring and screening of harmful and bloom-forming algae in coastal waters with updated functional screening database

Climate change and anthropogenic pressures alter phytoplankton phenology, distribution, and bloom frequency. Healthy phytoplankton communities are crucial for biogeochemical processes, blue carbon sequestration, and climate change mitigation. By employing high-throughput 18S V4 rRNA metabarcoding, we addressed the need for profiling phytoplankton community and response mechanisms in urbanized coastal ecosystems. Through an extensive literature review, we further integrated available databases and updated taxonomic information to construct a functional screening database, comprising 469 algal species identified from literature as toxin-producing or bloom-forming, affecting ecosystem or human health. Results showed an abundance of Mediophyceae and Trebouxiophyceae enriched among the phytoplankton communities in areas with overarching anthropogenic input sources such as estuarine freshwater and wastewater effluents, respectively, with distributions inferred to associate with water current exchanges. The study also expanded current baseline inventory for studied Hong Kong waters, revealing novel harmful algae profiles dominated primarily by Karlodinium veneficum and Cyclotella choctawhatcheeana. We found that harmful algae compositions in various coastal zones were selectively driven by indicators such as salinity, pH, and nitrogen species loading during the wet season. The incorporation of phytoplankton community monitoring and harmful algae screening in this study streamlines and empowers current molecular-based coastal marine surveillance. This not only facilitates baseline monitoring and mechanistic understanding of harmful and bloom-forming algae occurrence patterns but also advances molecular approaches to inform effective management of water resources and mitigation strategies on a global scale.