The genus Alexandrium often forms harmful algal blooms causing human illness and large-scale mortality of fish and shellfish. Thus, Alexandrium bloom dynamics are primary concerns for scientists, government officials, aquaculture farmers, and the public. To understand bloom dynamics, mortality due to predation needs to be assessed; however, interactions between many Alexandrium species and their potential predators have not previously been reported. Thus, feeding by five common heterotrophic dinoflagellates (Oxyrrhis marina, Gyrodinium dominans, Polykrikos kofoidii, Pfiesteria piscicida, and Oblea rotunda) and a naked ciliate (Strombidinopsis sp.) on 12 Alexandrium species was examined. Furthermore, the growth and ingestion rates of P. kofoidii on A. minutum CCMP 1888 (previously A. lusitanicum), A. minutum CCMP 113, and A. tamarense were measured as a function of prey concentration. The growth rates of P. kofoidii on the other Alexandrium species at single high prey concentrations were measured, at which the growth rates on A. minutum CCMP 1888 and A. tamarense were saturated. Feeding occurrence by these predators on 12 Alexandrium species could be categorized into 6 different prey groups. Each Alexandrium species was consumed by at least one predator; however, there was no Alexandrium species that was eaten by all six predators. Cells of A. minutum CCMP 1888, A. minutum CCMP 113, and A. tamarense were fed upon by four predators, but A. affine and A. pacificum by only one predator species, P. kofoidii or Strombidinopsis sp. Furthermore, A. minutum CCMP 1888 and A. tamarense supported high growth rates of P. kofoidii, but the other Alexandrium species did not support, but rather inhibited P. kofoidii growth. With increasing prey concentrations, the growth and ingestion rates of P. kofoidii on A. minutum CCMP 1888 and A. tamarense increased and became saturated, whereas those on A. minutum CCMP 113 continuously decreased. The maximum growth rates of P. kofoidii on A. tamarense and A. minutum CCMP 1888 were 1.010 and 0.765 d⁻¹, respectively, and P. kofoidii maximum ingestion rates were 26.2 and 11.1 ng C predator⁻¹d⁻¹, respectively. In contrast, the growth rates of P. kofoidii on the other Alexandrium species at single high prey concentrations were almost zero (A. pacificum) or negative. Based on the feeding occurrence and growth and ingestion rates of predators on 12 Alexandrium species, it is suggested that common heterotrophic protistan predators respond differently to different Alexandrium species, and thus ecological niches of the Alexandrium species may be different from each other. These results may provide an insight into the roles of protistan predators in bloom dynamics of Alexandrium species.

亚历山大藻属经常形成有害的藻华，引起人类疾病以及鱼类和贝类的大规模死亡。因此，亚历山大藻绽放动态是科学家，政府官员，水产养殖农民和公众关注的主要问题。为了了解水华的动态，需要评估捕食导致的死亡率；但是，以前没有关于许多亚历山大藻物种与其潜在掠食者之间相互作用的报道。因此，进料通过五种常见异鞭毛藻（Oxyrrhis码头，环沟dominans，Polykrikos kofoidii，腰鞭毛虫Pfiesteria piscicida和Oblea圆形大厅）和裸纤毛虫（检查了12种亚历山大藻的Strombidinopsis sp。）。此外，生长和摄取率P. kofoidii上A.藻CCMP 1888（以前A. lusitanicum），A.藻CCMP 113，和A.藻测量为猎物浓度的函数。的生长速率P. kofoidii另一方面亚历山大在单一高浓度猎物物种进行测定，在该上的生长速率A.藻CCMP 1888和A.藻饱和。这些捕食者在12个亚历山大大帝上觅食物种可以分为6个不同的猎物组。每个亚历山大种类都被至少一个捕食者所消耗。但是，六个捕食者都没有食用亚历山大藻。A. minutum CCMP 1888，A。minutum CCMP 113和A. tamarense的细胞由四个捕食者喂养，而A. affine和A. pacificum仅由一种捕食者物种P. kofoidii或Strombidinopsis sp。饲养。此外，A. minutum CCMP 1888和A. tamarense支持P. kofoidii的高生长速率，但其他亚历山大该物种不支持，而是抑制了波氏假单胞菌的生长。随着猎物浓度，生长和摄取率P. kofoidii上A.藻CCMP 1888和A.藻增加并且变得饱和，而那些对A.藻CCMP 113连续地下降。的最大生长速率P. kofoidii上A.藻和A.藻CCMP 1888分别为1.010和0.765 d ^-1，分别和P. kofoidii最大摄取率分别为26.2和11.1纳克Ç捕食^-1 d ^-1，分别。相比之下，在其他单一高猎物浓度的亚历山大种类上，P。kofoidii几乎为零（A. pacificum）或为负。基于所述馈送发生和12个天敌的生长和摄食率亚历山大物种，因此建议公共异原生生物天敌有不同的反应，以不同的亚历山大物种，以及由此的生态位亚历山大物种可以是彼此不同的。这些结果可能提供洞察力的protistan捕食者在亚历山大藻物种绽放动态中的作用。