In order to better understand the seasonal variations in the phytoplankton community structure in the Bohai Sea (BS) and the North Yellow Sea (NYS), we carried out three cruises during 12 to 24 April 2019, 8 to 18 June 2019, and 12 to 22 October 2019. A total of 212 taxa (75 genera and three phyla) were identified, among which 83 taxa in 40 genera, 96 taxa in 43 genera, and 151 taxa in 62 genera were found in spring, summer, and autumn, respectively. Diatoms including Paralia sulcata and Coscinodiscus granii were the most dominant phytoplankton group during the three seasons, while several species of dinoflagellates, e.g., Scrippsiella troichoidea, Tripos massiliensis f. armatus, Gyrodinium spirale, and Prorocentrum minimum were found in warmer, saltier, and nutrient-poor waters. The diversity index of phytoplankton community was highest in autumn and lowest in summer. Based on cluster and multidimensional scaling analyses, the phytoplankton community of the BS and the NYS was divided into three ecological provinces: the BS, the coastal area, and the NYS. These three ecological provinces differed in physicochemical properties induced by the complicated water masses and circulations. Due to the influence of nutrient concentration, the phytoplankton diversity had the highest value in autumn, followed by spring, and the smallest in summer.

Gambierdiscus is a dinoflagellate genus widely distributed throughout tropical and subtropical regions. Some members of this genus can produce a group of potent polycyclic polyether neurotoxins responsible for ciguatera fish poisoning (CFP), one of the most significant food-borne illnesses associated with fish consumption. Ciguatoxins and maitotoxins, the two major toxins produced by Gambierdiscus, act on voltage-gated channels and TRPA1 receptors, consequently leading to poisoning and even death in both humans and animals. Over the past few decades, the occurrence and geographic distribution of CFP have undergone a significant expansion due to intensive anthropogenic activities and global climate change, which results in more human illness, a greater public health impact, and larger economic losses. The global spread of CFP has led to Gambierdiscus and its toxins being considered an environmental and human health concern worldwide. In this review, we seek to provide an overview of recent advances in the field of Gambierdiscus and its associated toxins based on the existing literature combined with re-analyses of current data. The taxonomy, phylogenetics, geographic distribution, environmental regulation, toxin detection method, toxin biosynthesis, and pharmacology and toxicology of Gambierdiscus are summarized and discussed. We also highlight future perspectives on Gambierdiscus and its associated toxins.