Effect of ocean acidification on diatom frustule stability

Chair: Sue-Ann Watson

Linn J. Hoffmann (1)*, Emma Kearney (1)

1 Department of Botany, University of Otago, Dunedin, New Zealand

Background
Marine diatoms play a significant role in the global carbon and silica cycles. Their silica frustules are extremely stable and provide a very effective defence mechanism against copepod grazers. However, many environmental factors can influence silica accumulation of marine diatoms, including iron availability, grazer presence, and pCO2 and thus potentially affecting frustule stability. It has been shown that diatom frustules were significantly more stable when the cells were grown under low iron availability. Here, we investigate if the reported changes in cellular silica quota for diatoms grown under different pCO2 values have a similar effect on frustule stability.

Methods
The mechanical stability of diatoms grown under ambient and future pCO2 was tested by crushing the cells using calibrated microneedles under a microscope.

Findings
Cultures grown under high pCO2 showed systematically lower frustule stability compared to the same species grown under ambient pCO2.

Conclusions
We conclude that ocean acidification might affect diatom frustule stability in the natural environment and thus potentially affect diatom grazing protection. As the feeding success of copepods is partly dependent on the mechanical strength of diatom frustules, any alteration in frustule stability could significantly affect phytoplankton community composition in the future.