Newly recorded bloom-forming dinoflagellate Gymnodinium impudicum in Haizhou Bay, Yellow Sea, China

With the development of industrialization and aquaculture in Jiangsu and Shandong Provinces along the South Yellow Sea coast, China, eutrophication has greatly intensified in the region, resulting in frequent occurrence of diverse harmful algal blooms. An algal bloom formed by a chain-forming dinoflagellate species was recorded in the Haizhou Bay, South Yellow Sea, in September 2020. The causative species was isolated and studied in morphology, molecular phylogeny, pigment profile, presence of paralytic shellfish toxins, and acute toxicity. The loop-shaped apical groove running anticlockwise around the apex, the presence of peridinin as characteristic pigment, as well as a single phylogenic clade of 28S ribosomal DNA (100% posterior probability), defined this species as Gymnodinium impudicum, a non-toxic species that exhibited no obvious biotoxicity to the rotifer Brachionus plicatilis, the copepod Artemia salina, and the shrimp Neomysis awatschensis. Gymnodinium impudicum is typically distributed in coastal waters with high nitrate concentrations, where it reaches a maximum density of 2.6x10(5) cells/L. This is the first report of a G. impudicum bloom in the Yellow Sea; however, G. impudicum blooms may have been misidentified or underreported in Haizhou Bay due to the species morphological similarity with G. catenatum. A combination of multiple methods is recommended to accurately identify new algal bloom species.

Automated summary

With the development of industrialization and aquaculture in Jiangsu and Shandong Provinces, eutrophication has intensified in the South Yellow Sea coast, resulting in frequent harmful algal blooms. A study identified a non-toxic algal bloom caused by Gymnodinium impudicum in Haizhou Bay. This species has specific morphological and molecular characteristics, but may be easily misidentified or underreported. The use of multiple methods is recommended for accurate identification of new algal bloom species.