Thicker shells reduce copepod grazing on diatoms

The diatom frustule provides partial protection against copepods, yet we do not know the mechanism behind the reduced grazing. We used direct observations of copepod-diatom interactions to compare rejection frequency and prey-handling times of diatoms with different degrees of silica content in three differently sized species. 
We compared rejection frequency and prey-handling times of thick- and thin-shelled cells of the diatoms Cyclotella cryptica, Thalassiosira weissflogii, and Ditylum brightwellii. We found that for all three species, that thick-shelled cells were more frequently rejected by the copepods subsequent to being captured. 
The copepod prey-handling times, i.e., the time from the copepod reacted to the prey until it had been ingested or rejected, generally increased with prey size. We further found that thicker-shelled cells in the two larger species, T. weissflogii and D. brightwellii, were handled for so long that the copepods lose time for foraging. Both of these mecha...

硅藻壳（diatom frustule）可对桡足类（copepods）提供部分防御，但目前学界尚未明确其降低摄食率的内在机制。本研究通过直接观测桡足类与硅藻的相互作用，对比了三种不同体型大小的硅藻物种中硅质含量各异的个体的拒食频率（rejection frequency）与猎物处理时长（prey-handling times）。
我们针对隐花圆筛藻（Cyclotella cryptica）、威氏海链藻（Thalassiosira weissflogii）以及明亮透侧藻（Ditylum brightwellii）的厚壳与薄壳细胞，开展了拒食频率与猎物处理时长的对比分析。研究结果显示，针对上述三个物种，厚壳硅藻细胞在被桡足类捕获后，遭拒食的频率显著更高。
桡足类的猎物处理时长，即从桡足类对猎物作出反应，直至其将猎物吞食或拒食的时间跨度，通常随猎物体型增大而延长。本研究进一步发现，在两个体型更大的物种——威氏海链藻（T. weissflogii）与明亮透侧藻（Ditylum brightwellii）中，厚壳细胞的处理时长过长，导致桡足类损失了觅食时间。上述两种机制……