Dinoflagellates from the globally distributed genus Alexandrium are known to produce both paralytic shellfish toxins (PST) and uncharacterized bioactive extracellular compounds (BEC) with allelopathic, ichthyotoxic, hemolytic and cytotoxic activities. In France, blooms of Alexandrium minutum appear generally during the spawning period of most bivalves. These blooms could therefore alter gametes and/or larval development of bivalves, causing severe issues for ecologically and economically important species, such as the Pacific oyster Crassostrea (=Magallana) gigas. The aim of this work was to test the effects of three strains of A. minutum producing either only PST, only BEC, or both PST and BEC upon oyster gametes, and potential consequences on fertilization success. Oocytes and spermatozoa were exposed in vitro for 2 hours to a range of environmentally realistic A. minutum concentrations (10 to 2.5 × 10⁴ cells mL^-1). Following exposure, gamete viability and reactive oxygen species (ROS) production were assessed by flow cytometry, spermatozoa motility and fertilization capacities of both spermatozoa and oocytes were analysed by microscopy. Viability and fertilization capacity of spermatozoa and oocytes were drastically reduced following exposure to 2.5 × 10⁴ cells mL^-1 of A. minutum. The BEC-producing strain was the most potent strain decreasing spermatozoa motility, increasing ROS production of oocytes, and decreasing fertilization, from the concentration of 2.5 × 10³ cells mL^-1. This study highlights the significant cellular toxicity of the BEC produced by A. minutum on oyster gametes. Physical contact between gametes and motile thecate A. minutum cells may also contribute to alter oyster gamete integrity. These results suggest that oyster gametes exposure to A. minutum blooms could affect oyster fertility and reproduction success.

已知来自全球分布的亚历山大藻属的甲藻会产生麻痹性贝类毒素 (PST) 和具有化感作用、鱼毒、溶血和细胞毒活性的未表征的生物活性细胞外化合物 (BEC)。在法国，大多数双壳类动物的产卵期通常会出现小亚历山大藻（Alexandrium minutum）的花朵。因此，这些水华可能会改变双壳类的配子和/或幼虫发育，对生态和经济上重要的物种造成严重问题，例如太平洋牡蛎Crassostrea (= Magallana) gigas。这项工作的目的是测试三种A. minutum菌株的效果牡蛎配子只产生 PST、只产生 BEC 或同时产生 PST 和 BEC，以及对受精成功的潜在影响。卵母细胞和精子在体外暴露于一系列环境现实的A. minutum浓度（10 到 2.5 × 10 ⁴细胞 mL ^-1）中2 小时。暴露后，通过流式细胞术评估配子活力和活性氧 (ROS) 产生，通过显微镜分析精子和卵母细胞的精子活力和受精能力。暴露于 2.5 × 10 ⁴细胞 mL ^-1的A. minutum 后，精子和卵母细胞的活力和受精能力显着降低. 产生 BEC 的菌株是最有效的菌株，从 2.5 × 10 ³细胞 mL ^-1的浓度开始降低精子活力、增加卵母细胞的 ROS 产生和减少受精。这项研究强调了A. minutum产生的 BEC对牡蛎配子的显着细胞毒性。配子和活动的鞘膜A. minutum细胞之间的物理接触也可能有助于改变牡蛎配子的完整性。这些结果表明牡蛎配子暴露于A. minutum开花可能会影响牡蛎的繁殖力和繁殖成功率。