Ocean Acidification: Threats to Diatoms and Marine Food Chains

The pH of the oceans is gradually decreasing, making waters more acidic – a phenomenon known as ocean acidification. This chemical change, directly linked to the absorption of atmospheric carbon dioxide (CO₂), affects the smallest but most influential organisms in the plankton, diatoms. A new study by Flinders University highlights the risk that this acidification poses to the ability of these microalgae to capture carbon and support marine food chains.

What the study reveals: a threat to diatoms' role in the carbon cycle

Researchers found that under lower pH conditions, diatoms show signs of physiological stress. Their ability to form their siliceous frustules, essential structures for their growth, is compromised, slowing down cell division. Consequently, the amount of organic carbon they can fix decreases, weakening the natural process of carbon sequestration into the deep ocean.

This reduction in diatom productivity has cascading effects. Diatoms form the base of most marine food webs; they feed zooplankton, which in turn feed fish, cephalopods, and marine mammals. If their abundance declines, the availability of food for these trophic levels decreases, threatening biodiversity and fisheries stability. The study suggests that these effects could amplify regionally, particularly in high-productivity zones where diatoms dominate.

How the study was conducted: experimental methods and data analysis

Teams from Flinders University combined laboratory experiments with field observations. Diatom cultures were exposed to pH levels replicating future acidification scenarios. Scientists measured cell growth, frustule formation, and carbon fixation rates using mass spectrometry and electron microscopy techniques. Meanwhile, they collected seawater samples from several coastal sites to compare laboratory observations with natural conditions.

To broaden the context, researchers also consulted public databases on ocean pH measurements and dissolved CO₂ concentrations, but no additional data could be integrated in detail into the study – information not confirmed at this stage. The combination of these approaches provided a coherent picture of the effects of acidification on diatoms.