The toxic dinoflagellate Karlodinium veneficum forms fish killing blooms in temperate estuaries worldwide. These blooms have variable toxicity which may be related to bloom stage and in situ growth rates of the constituent K. veneficum cells. Measurement of in situ growth rates is challenging and methods such as the mitotic index technique require knowledge of the dynamics of cell division. In order to better understand these dynamics, we determined the duration of cell division (t_d) in four geographically distinct laboratory strains of K. veneficum at three different environmentally relevant temperatures. The results demonstrated that the t_d value for each strain, growing at strain-specific optimal temperatures, was 1.6 ± 0.1 h. This value corresponded to a range of growth rates from 0.17 ± 0.08 d⁻¹ to 0.62 ± 0.07 d⁻¹. Equivalent values of t_d spread across four geographically distinct laboratory strains and a nearly fourfold range of growth rates implies that 1.6 h represents the t_d value of K. veneficum. Additionally, temperature conditions yielding this value for t_d and the highest growth rates varied among strains, indicating cold-adapted (Norway), warm-adapted (Florida, USA), and eurythermally-adapted (Maryland, USA) strains. These differences have been apparently retained in culture over many years, indicating a conserved genetic basis that suggests distinct thermal ecotypes of the morphospecies K. veneficum. This knowledge together with the first estimate of t_d for K. veneficum will be useful in future field studies aimed at correlating bloom toxicity with in situ growth rate using the mitotic index technique.

有毒的甲藻卡洛丁藻 (Karlodinium v​​eneficum) 在全世界温带河口形成了导致鱼类死亡的水华。这些水华具有不同的毒性，可能与水华阶段和组成 K.veneficum 细胞的原位生长速率有关。原位生长速率的测量具有挑战性，有丝分裂指数技术等方法需要了解细胞分裂的动力学。为了更好地理解这些动态，我们确定了四种地理位置不同的 K. veneficum 实验室菌株在三种不同的环境相关温度下的细胞分裂持续时间 (t _d )。结果表明，每个菌株在特定菌株的最佳温度下生长的 t _d 值为 1.6 ± 0.1 小时。该值对应的生长速率范围为 0.17 ± 0.08 d ⁻¹ 至 0.62 ± 0.07 d ⁻¹ 。 t _d 的等效值分布在四种地理位置不同的实验室菌株中，并且生长速率的近四倍范围意味着 1.6 小时代表 K. Veneficum 的 t _d 值。此外，产生该 t _d 值的温度条件和最高生长速率因菌株而异，表明冷适应（挪威）、热适应（美国佛罗里达）和广温适应（美国马里兰州） ）菌株。这些差异显然已在培养物中保留多年，表明保守的遗传基础表明 K. veneficum 形态种具有独特的热生态型。这些知识以及对 K. veneficum t _d 的首次估计将有助于未来的实地研究，旨在使用有丝分裂指数技术将水华毒性与原位生长率相关联。