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SUMMARY Species of the marine benthic dinoflagellate genus Gambierdiscus are the principal cause of Ciguatera fish poisoning. This genus has been recorded from tropical to temperate oceans, although Gambierdiscus species have rarely been found in Chinese waters. Our work revealed the morphological and genetic characteristics of three potentially toxic Gambierdiscus species observed in the temperate to subtropical waters of China. The fine thecal morphology was determined based on light microscopy and scanning electron microscopy analyses, and these species were also characterized by sequencing the D1–D3 and D8–D10 regions of the LSU rDNA. The morphological and genetic data indicated that these three Gambierdiscus species were G. pacificus, G. australes and G. caribaeus. This work provides the first report of these species in Chinese waters, which increases the known species distribution of this genus.

Aureococcus anophagefferens is a harmful alga that dominates plankton communities during brown tides in North America, Africa, and Asia. Here, RNA-seq technology was used to profile the transcriptome of a Chinese strain of A. anophagefferens that was grown on urea, nitrate, and a mixture of urea and nitrate, and that was under N-replete, limited and recovery conditions to understand the molecular mechanisms that underlie nitrate and urea utilization. The number of differentially expressed genes between urea-grown and mixture N-grown cells were much less than those between urea-grown and nitrate-grown cells. Compared with nitrate-grown cells, mixture N-grown cells contained much lower levels of transcripts encoding proteins that are involved in nitrate transport and assimilation. Together with profiles of nutrient changes in media, these results suggest that A. anophagefferens primarily feeds on urea instead of nitrate when urea and nitrate co-exist. Furthermore, we noted that transcripts upregulated by nitrate and N-limitation included those encoding proteins involved in amino acid and nucleotide transport, degradation of amides and cyanates, and nitrate assimilation pathway. The data suggest that A. anophagefferens possesses an ability to utilize a variety of dissolved organic nitrogen. Moreover, transcripts for synthesis of proteins, glutamate-derived amino acids, spermines and sterols were upregulated by urea. Transcripts encoding key enzymes that are involved in the ornithine-urea and TCA cycles were differentially regulated by urea and nitrogen concentration, which suggests that the OUC may be linked to the TCA cycle and involved in reallocation of intracellular carbon and nitrogen. These genes regulated by urea may be crucial for the rapid proliferation of A. anophagefferens when urea is provided as the N source.

SUMMARY The genus Ostreopsis contains benthic and potentially toxic species that are distributed in tropical and temperate regions. In this study, we present the first report of observations of Ostreopsis cf. ovata and O. lenticularis in Chinese waters. Isolates were characterized morphologically based on LM and SEM, and phylogenetic analyses were conducted by sequencing the LSU rDNA (D1–D3), ITS region (ITS1‐5.8S‐ITS2) and SSU rDNA. The morphology of O. cf. ovata Hainan strains was similar to the original description of O. ovata, despite differences in cell size. The morphology of O. lenticularis Hainan strains was similar to the original description, although both deviations of cell dimensions and different kinds of thecal pores were observed. The plate formula for the Ostreopsis Hainan strains was arranged in Kofoid's system tabulation of Po, 3′, 7′′, Vp, Rp, 1p, 5′′′, 2′′′′. The O. cf. ovata and O. lenticularis Hainan strains showed close relationships with strains collected from the Pacific Ocean based on the sequences of both LSU rDNA and ITS region. The genetic differences (p‐distances) of SSU rDNA sequences of the Ostreopsis cf. ovata Hainan strain were 0.0096 and 0.0447 different from those of a Malaysian strain and a South Korean strain, respectively. This work identifies the first occurrence of Ostreopsis with the morphology and phylogeny of Hainan strains in Chinese waters.

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