Silicified cell walls as a defensive trait in diatoms

Monday 29 Apr 19


Marina Mohr
PhD student
DTU Aqua
+45 91 94 03 42



Rodrigo Almeda
DTU Aqua


Thomas Kiørboe
DTU Aqua
+45 35 88 34 01

Diatoms contribute nearly half of the marine primary production. These microalgae differ from other phytoplankton groups in having a silicified cell wall, which is the strongest known biological material relative to its density. While it has been suggested that a siliceous wall may have evolved as a mechanical protection against grazing, empirical evidence of its defensive role is limited.

Here, we experimentally demonstrate that grazing by adult copepods and nauplii on diatoms is approximately inversely proportional to their silica content, both within and among diatom species. While a six-fold increase in silica content leads to a four-fold decrease in copepod grazing, silicification provides no protection against protozoan grazers that directly engulf their prey.

We also found that the wall provides limited protection to cells ingested by copepods, since less than 1% of consumed cells were alive in the faecal pellets. Moreover, silica deposition in diatoms decreases with increasing growth rates, suggesting a possible cost of defence. Overall, our results demonstrate that thickening of silica walls is an effective defence strategy against copepods. This suggests that the plasticity of silicification in diatoms may have evolved as a response to copepod grazing pressure, whose specialized tools to break silicified walls have coevolved with diatoms.

In conclusion, our study quantifies for the first time key fitness components of the single most important phytoplankton group in the ocean.

Pančić M, Torres RR, Almeda R and Kiørboe T (2019) Silicified cell walls as a defensive trait in diatoms Proceedings of the Royal Society B: Biological Sciences

Figure shows TEM image of diatom frustules by Marina Pančić.
24 MAY 2019