Illustrations of diatoms, copepods, copepod cues, and thick-shelled diatoms

Diatoms increase their defense when they smell danger

Wednesday 19 Aug 20



Thomas Kiørboe
DTU Aqua
+45 35 88 34 01

Diatoms live in a protective silica shell. A new study demonstrates that diatoms increase the thickness of the shell in the presence of their copepod predators but at the cost of a lower growth rate.

The silica shell of diatoms is the strongest known biological material, and only a few grazers are able to crack the shell and consume its inhabitant. When adding chemical cues extracted from copepods to a suspension of diatoms, the cells increase their silica content by up to 35 %, thereby significantly reducing the ability of copepods to eat the cells. The diatoms, however, have to ‘pay’ for their enhanced defense by reducing their growth rate, but this cost is warranted by the higher chance of survival. 

Diatoms account for 40 % of the oceans’ primary production. The demonstrated trade-off between growth and survival helps explain the very high diversity of diatoms in the oceans, and the variation – by a factor of 10 – in silica contents of diatoms. Whether or not the cells are consumed by copepods depends on the silica content and has implications for the fate of the carbon dioxide fixed by the diatoms: rapidly sinking copepod fecal pellets transport carbon to the ocean interior and thus play an important role in the oceans’ ability to sequester carbon.

Read the paper here:


Grønning J, Kiørboe T (2020) Diatom defence: Grazer induction and cost of shell-thickening. Funct Ecol
22 APRIL 2021