Multiple dinoflagellate species from the genus Karlodinium have been well known to form massive and toxic blooms that consequently cause fish kills in many coastal waters around the world. Karlodinium australe is a mixotrophic and potentially ichthyotoxic species associated with fish kills. Here, we investigated phagotrophy of K. australe (isolate KaJb05) established from a bloom event in the West Johor Strait, Malaysia, using several prey species (phytoplankton, zooplankton, and larval fish). The results showed that K. australe ingested relatively small prey cells of co-occurring microalgae by direct engulfment, while it fed on larger prey cells of microalgae by tube feeding. The results of animal exposure bioassays using rotifer (Brachionus plicatilis), brine shrimp (Artemia salina), and larval fish (Oryzias melastigma) demonstrated that phagotrophy (in terms of the trophic mode of the dinoflagellate), or micropredation (in terms of the mechanism of lethal effects on prey), played a more important role than the toxicity did in causing the lethal effects of K. australe on these aquatic animals under low cell densities of K. australe, while the mortalities of animals observed in the exposure to cell lysates of K. australe were solely caused by the toxicity. A comparison of the lethal effects between K. australe and K. veneficum revealed that the lethal effect of K. australe on rotifers was much stronger than that of K. veneficum at all cell densities applied in the experiments and the more "aggressive" micropredation of K. australe is suggested to explain the difference in lethal effect between K. austale and K. veneficum. Our results may explain why K. australe exhibited fish killings during moderate blooms at cell densities < 2.34 × 10⁶ cells L⁻¹, whereas K. veneficum was observed to cause massive fish kills only if the cell density was above 10⁷ cells L⁻¹. We believe these findings provide new insights into the ecological consequences of phagotrophy exhibited in some mixotrophic and harmful algae such as species of Karlodinium and of HAB events in general.

众所周知，来自Karlodinium属的多种鞭毛藻物种会形成大量有毒的花开，从而在世界许多沿海水域造成鱼类死亡。卡尔丁草是一种混养性鱼类，可能与鱼杀害有关，具有鱼腥毒素。在这里，我们调查的phagotrophy K. AUSTRALE从西方柔佛海峡，马来西亚华事件成立（株KaJb05），使用多种猎物（浮游植物，浮游动物和仔鱼）。结果表明，澳洲K通过直接吞噬摄入了相对较小的共生微藻捕食细胞，而通过管饲喂食了较大的微藻捕食细胞。使用轮虫进行动物暴露生物测定的结果（Brachionus plicatilis，盐水虾（Artemia salina）和幼体鱼（Oryzias melastigma）证明吞噬营养（就鞭毛的营养模式而言）或微捕食（就对猎物的致死作用机理而言）发挥了作用。比毒性更重要的作用，造成的致命影响做了K. AUSTRALE对下的低细胞密度，这些水生动物K. AUSTRALE，而在暴露于细胞裂解液观察动物的死亡率K. AUSTRALE为唯一由引起毒性。比较澳大利亚K. veneficum和K. veneficum的致死作用。在实验中使用的所有细胞密度下，轮虫上的K. australe都比K. veneficum强大得多，并且建议对K. australe进行更“积极”的微捕食，以解释K. austale和K. veneficum在致死作用上的差异。我们的研究结果可以解释为什么K. AUSTRALE期间在细胞密度<2.34×10中等开花表现出鱼杀害⁶传感器L ^{- 1}，而K. veneficum观察到造成大规模鱼类死亡仅当细胞密度为10以上⁷传感器L ^{- 1个}。我们相信，这些发现为某些营养混合和有害藻类（如Karlodinium物种和HAB事件）表现出的吞噬营养的生态后果提供了新的见解。