The dinoflagellate genus Alexandrium comprises species that produce highly potent neurotoxins known as paralytic shellfish toxins (PST), and bioactive extracellular compounds (BEC) of unknown structure and ecological significance. The toxic bloom-forming species, Alexandrium minutum, is distributed worldwide and adversely affects many bivalves including the commercially and ecologically important Pacific oyster, Crassostrea gigas. In France, recurrent A. minutum blooms can co-occur with C. gigas spawning and larval development, and may endanger recruitment and population renewal. The present study explores how A. minutum affects oyster early development by exposing embryos and larvae, under controlled laboratory conditions, to two strains of A. minutum, producing only BEC or both PST and BEC. Results highlight the major role of BEC in A. minutum toxicity upon oyster development. The BEC strain caused lysis of embryos, the most sensitive stage to A. minutum toxicity among planktonic life stages. In addition, the non-PST-producing A. minutum strain inhibited hatching, disrupted larval swimming behavior, feeding, growth, and induced drastic decreases in survival and settlement of umbonate and eyed larvae (9 and 68 %, respectively). The findings indicated PST accumulation in oyster larvae (e.g. umbonate stages), possibly impairing development and settlement of larvae in response to the PST-producing strain. This work provides evidences that A. minutum blooms could hamper settlement of shellfish.

甲藻属亚历山大包括产生高度称为麻痹性贝毒素（PST）强效神经毒素种类，和未知的结构和生态学意义的生物活性细胞外的化合物（BEC）。有毒的水华形成物种亚历山大草（Alexandrum minutum）分布于世界各地，并对许多双壳类鱼类产生不利影响，包括商业上和生态上重要的太平洋牡蛎Crassostrea gigas。在法国，反复微小亚历山大藻大量繁殖可与共同出现长牡蛎产卵和幼虫发育，并可能危及招募和人口续约。本研究探讨了A. minutum通过在受控的实验室条件下，将胚胎和幼虫暴露于两种仅产BEC或只产生PST和BEC的A. minutum菌株，从而影响牡蛎的早期发育。结果突出了BEC在牡蛎发育过程中对A. minutum毒性的主要作用。BEC菌株引起了胚胎的溶解，这是浮游生命阶段中对A. minutum毒性最敏感的阶段。此外，不产生PST的A. minutum菌株抑制了孵化，破坏了幼体的游泳行为，进食，生长，并引起了伞形和有眼幼虫的存活和沉降的急剧下降（分别为9％和68％）。研究结果表明PST在牡蛎幼虫中积累（例如卵期），可能会损害对产PST的菌株的幼虫发育和沉降。这项工作提供了证据，证明A. minutum开花可能会妨碍贝类的沉积。