We have assessed the effect of copepod chemical cues on the diel feeding rhythms of heterotrophic and mixotrophic marine protists. All phagotrophic protists studied exhibited relatively high diurnal feeding rates. The magnitude of the diel feeding rhythm, expressed as the quotient of day and night ingestion rates, was inversely related to the time that phagotrophic protists were maintained in the laboratory in an environment without predators. In the case of the recently isolated ciliate Strombidium arenicola, the rhythm was lost after a few months. When challenged with chemical alarm signals (copepodamides) from the copepod Calanus finmarchicus at realistic concentrations (0.6–6 pM), S. arenicola partially re-established diurnal feeding. Conversely, the amplitude of the diel feeding rhythm for the ciliate Mesodinium rubrum was not affected by copepodamides, although the 24-h integrated food intake increased by approximately 23%. For the dinoflagellates Gyrodinium dominans and Karlodinium armiger, copepodamides significantly reduced the amplitude of their diel feeding rhythms; significant positive effects on total daily ingestion were only observed in G. dominans. Finally, the dinoflagellate Oxyrrhis marina, isolated >20 years ago, showed inconsistent responses to copepodamides, except for an average 6% increase in its total ingestion over 24 h. Our results demonstrate that the predation risk by copepods affects the diel feeding rhythm of marine protists and suggests a species-specific response to predation threats.

我们已经评估了桡足类化学线索对异养和混养海洋原生生物的昼夜摄食节律的影响。所有研究的吞噬原生生物都表现出相对较高的昼夜摄食率。昼夜摄食节律的大小，表示为昼夜摄取率的商，与吞噬性原生生物在实验室中没有捕食者的环境中维持的时间成反比。在最近分离的纤毛虫Strombidium arenicola的情况下，几个月后节律消失了。当受到来自桡足类Calanus finmarchicus 的化学警报信号（桡足类）的挑战时，实际浓度（0.6-6 pM），S. arenicola部分重新建立了昼夜喂养。相反，尽管 24 小时综合食物摄入量增加了约 23%，但纤毛虫Mesodinium rubrum的日食节律幅度不受桡足类动物的影响。对于甲藻Gyrodinium dominans和Karlodinium armiger，桡足类动物显着降低了它们的昼夜摄食节律的幅度；仅在G. dominans 中观察到对每日总摄入量的显着积极影响。最后，甲藻Oxyrrhis marina20 年前分离的 ，对桡足类动物表现出不一致的反应，除了在 24 小时内其总摄入量平均增加 6%。我们的研究结果表明，桡足类动物的捕食风险会影响海洋原生生物的饮食节律，并表明对捕食威胁的物种特异性反应。