Ingestion and clearance rates of Copepods@en

Feeding activity, selective grazing and the potential grazing impact of two dominant grazers of the Polar Frontal Zone, Calanus simillimus and Rhincalanus gigas, and of copepods < 2 mm were investigated with incubation experiments in the course of an iron fertilized diatom bloom in November 2000. All grazers were already actively feeding in the low chlorophyll waters prior to the onset of the bloom. C. simillimus maintained constant clearance rates and fed predominantly on diatoms. R. gigas and the small copepods strongly increased clearance and ingestion of diatoms in response to their enhanced availability. All grazers preyed on microzooplankton, most steadily on ciliates, confirming the view that pure herbivory appears to be the exception rather than the rule in copepod feeding. The grazers exhibited differences in feeding behavior based on selectivity indices. C. simillimus and R. gigas showed prey switching from dinoflagellates to diatoms in response to the phytoplankton bloom. All grazers most efficiently grazed on large diatoms leading to differences in daily losses for large and small species, e.g. Corethron sp. or Thalassionema nitzschioides. Species-specific diatom mortality rates due to grazing suggest that the high feeding activity of C. simillimus prior to and during the bloom played a role in shaping diatom population dynamics2000年11月，在铁富集硅藻水华（iron fertilized diatom bloom）期间，本研究通过培养实验探究了极锋带（Polar Frontal Zone）的两类优势摄食者——相似哲水蚤（Calanus simillimus）与大角隆哲水蚤（Rhincalanus gigas），以及体长小于2mm的桡足类（copepods <2 mm）的摄食活性、选择性摄食行为及其潜在牧食效应。所有受试摄食者在水华爆发前的低叶绿素水体中已呈现活跃摄食状态。相似哲水蚤保持稳定的清滤率（clearance rates），且主要以硅藻为食。大角隆哲水蚤与小型桡足类则随硅藻可获得性提升，其清滤率（clearance rates）与摄食率（ingestion rates）显著升高。所有摄食者均以微型浮游动物（microzooplankton）为食，其中对纤毛虫类（ciliates）的摄食最为稳定，这证实了“纯植食性在桡足类摄食中仅为特例而非普遍规律”的学术观点。基于选择性指数（selectivity indices）分析，不同摄食者的摄食行为存在显著差异：相似哲水蚤与大角隆哲水蚤会响应浮游植物水华的发生，将摄食偏好由甲藻（dinoflagellates）转向硅藻。所有摄食者对大型硅藻的摄食效率最高，由此导致大型与小型硅藻物种（如冠盖藻属（Corethron sp.）、菱形海线藻（Thalassionema nitzschioides））的每日损失率存在差异。由牧食作用导致的物种特异性硅藻死亡率分析表明，相似哲水蚤在水华爆发前及水华期间的高摄食活性，对塑造硅藻种群动态具有关键作用。