Among dinoflagellates responsible for benthic harmful algal blooms, the genus Ostreopsis primarily described from tropical areas has been increasingly reported from subtropical and temperate areas worldwide. Several species of this toxigenic genus produce analogs of palytoxin, thus representing a major threat to human and environmental health. The taxonomy of several species needs to be clarified as it was based mostly on morphological descriptions leading in some cases to ambiguous interpretations and misidentifications. The present study aims at reporting a benthic bloom that occurred in April 2019 in Tahiti island, French Polynesia. A complete taxonomic investigation of the blooming Ostreopsis species was realized using light, epifluorescence and field emission electron microscopy and phylogenetic analyses inferred from LSU rDNA and ITS–5.8S rDNA regions. Toxicity of a natural sample and strains isolated from the bloom was assessed using both neuroblastoma cell-based assay and LC-MS/MS analyses. Morphological observations showed that cells were round to oval, large, 58.0–82.5 µm deep (dorso-ventral length) and 45.7–61.2 µm wide. The cingulum was conspicuously undulated, forming a ‘V’ in ventral view. Thecal plates possessed large pores in depressions, with a collar rim. Detailed observation also revealed the presence of small thecal pores invisible in LM. Phylogenetic analyses were congruent and all sequences clustered within the genotype Ostreopsis sp. 6, in a subclade closely related to sequences from the Gulf of Thailand and Malaysia. No toxicity was found on the field sample but all the strains isolated from the bloom were found to be cytotoxic and produced ostreocin D, a lower amount of ostreocins A and B and putatively other compounds. Phylogenetic data demonstrate the presence of this species in the Gulf of Thailand, at the type locality of O. siamensis, and morphological data are congruent with the original description and support this identification.

在引起底栖有害藻类大量繁殖的鞭毛藻中，主要从热带地区描述的Ostreopsis属已在全球亚热带和温带地区得到越来越多的报道。该产毒属的几种物种产生了palytoxin的类似物，因此对人类和环境健康构成了重大威胁。需要澄清几种物种的分类法，因为它主要基于形态学描述，在某些情况下会导致模棱两可的解释和错误识别。本研究旨在报告2019年4月在法属波利尼西亚的塔希提岛发生的底栖水华。盛开的骨质疏松症的完整分类学研究利用光，表面荧光和场发射电子显微镜以及从LSU rDNA和ITS–5.8S rDNA区域推断出的系统发育分析来实现该物种。使用基于神经母细胞瘤细胞的测定法和LC-MS / MS分析，评估了自然样品和从大花中分离出的菌株的毒性。形态学观察显示，细胞呈圆形到椭圆形，大，深58.0-82.5 µm（背腹长度），宽45.7-61.2 µm。扣带明显起伏，在腹面形成“ V”形。鞘管板在凹陷处具有大孔，并带有颈圈。详细的观察还发现在LM中看不见小的鞘孔。系统发育分析是一致的，所有序列都聚集在基因型Ostreopsis内sp。6，位于与泰国湾和马来西亚的序列密切相关的小节中。在田间样品上未发现毒性，但发现从大花中分离出的所有菌株均具有细胞毒性，并产生了ostreocin D，少量ostreocins A和B以及推定的其他化合物。系统发育数据表明，该物种存在于泰国湾（O. siamensis）类型的地方，形态数据与原始描述一致，并支持这种鉴定。