Diatom defence: Grazer induction and cost of shell-thickening

1. Diatoms account for 40 % of the ocean primary production and play a key role in the oceans’ ability to sequester carbon. The evolutionary success of diatoms and their role in ocean biogeochemistry are related to the siliceous shell that provide partial protection against grazing.
2. The structure and function of phytoplankton communities are governed by environmental constraints and organismal trade-offs. Defence mechanisms may help explain the high diversity of phytoplankton (incl. diatoms) in the ocean, but only if the defence comes at a cost. Defence costs have been notoriously difficult to demonstrate and quantify in marine phytoplankton.
3. Here, we demonstrate for seven species of planktonic diatoms that their shell thickens and their growth rate declines when cells are exposed to chemical cues from copepods, important predators of diatoms. The responses are proportional to the concentration of grazer cues, but are also highly variable, both between and within species.
4. At ou...