Data from: 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 mechanisms have implications for carbon sequestration and for
securing a large seed population at depth, and may be why many diatoms are
able to form blooms even in the presence of dense grazer
populations.

硅藻硅质壳（diatom frustule）可对桡足类（copepods）提供部分防御，但我们仍不清楚其降低桡足类摄食率的内在机制。本研究通过直接观测桡足类与硅藻的相互作用，比较了三种不同体型硅藻在不同硅含量下的拒食频率与猎物处理时长。我们对比了隐圈奇杆藻（Cyclotella cryptica）、威氏海链藻（Thalassiosira weissflogii）与光亮盒形藻（Ditylum brightwellii）这三种硅藻的厚壳与薄壳细胞的拒食频率及猎物处理时长。研究结果显示，对于所有三种硅藻，厚壳细胞在被桡足类捕获后被拒食的概率显著更高。桡足类的猎物处理时长，即从桡足类对猎物作出反应至其完成摄食或拒食的时长，通常随猎物体型增大而增加。此外我们还发现，在体型较大的两种硅藻——威氏海链藻（T. weissflogii）与光亮盒形藻（Ditylum brightwellii）——中，厚壳细胞的处理时长过长，导致桡足类损失了觅食所需的时间。上述两种机制均对碳封存及保障深海区域充足的藻种种群具有重要意义，这也可能解释了为何诸多硅藻即便在摄食者种群密度较高的环境中仍能形成藻华。