Taxonomy and toxin profile of harmful benthic Prorocentrum (Dinophyceae) species from the Xisha Islands, South China Sea

Some benthic Prorocentrum can produce okadaic acid (OA) and dinophysistoxins (DTXs) that cause diarrheic shellfish poisoning (DSP) in humans. The diversity and toxin profiles (OA and DTXs) of benthic Prorocentrum were investigated in the Xisha Islands, South China Sea. The benthic Prorocentrum was identified by both morphological features and molecular phylogenies. Morphologies were examined by light, fluorescence, and scanning electron microscopy, and phylogenetic analyses were based on partial large subunit (LSU) rDNA and ITS1-5.8S-ITS2 (ITS) region. Seven Prorocentrum species including P. borbonicum, P. caipirignum, P. concavum, P. elegans, P . cf. emarginatum, P. lima complex, and P. rhathymum were identified in Xisha Islands. Among them, P. borbonicum and P. elegans were recorded in Chinese waters for the first time. OA and DTXs contents of seven benthic Prorocentrum species were evaluated based on liquid chromatography-tandem mass spectrometry (LC-MS/MS). All Xisha Islands strains of P. lima complex produced OA at contents ranging from 1 663 to 3 816 fg/cell. P. caipirignum also generated OA at 407 fg/cell, but other five species had no detectable toxins. Besides, interestingly, two strains of P. lima complex produced DTX-1 only (74 and 183 fg/cell) and another two strains generated an isomer of OA and DTX-2. Our findings provided insight into the biodiversity of benthic Prorocentrum in the Xisha Islands and pointed out the potential risk of DSP in this area.