Grazer-induced changes on mechanical properties of diatoms frustule: A new proof for a watery arms race

We investigated changes in physiology and mechanical properties of diatoms exposed to chemical cues released by copepods Pseudodiaptomus annandalei. Our results showed that the diatoms Phaeodactylum tricornutum, Cylindrotheca closterium, Thalassiosira weissflogii, and Amphora coffeaeformis exhibited elevated growth rates and a substantial 2- to 50-fold increase in biogenic silica (BSi) content increase when exposed to the chemical cues except for Cyclotella sp. Atomic force microscopy and X-ray photoelectron spectroscopy analyses revealed that diatom frustules exhibited a remarkable 3- to 10-fold increase in modulus and a substantial 2- to 5-fold increase in hardness when they received grazing signals. The increase in the proportion of condensed silicon in the frustules could be the major reason for the more mechanically robust cells. Our results indicate that diatoms simultaneously increase their growth rate and robustness when exposed to copepod chemical cues. This study at the nanoscale enhanced our understanding of how diatoms respond to zooplankton predation in marine ecosystems.