Phytoplankton: The future of carbon reduction?

  • Plants remove carbon dioxide from the atmosphere and transform it into carbon-based organic compounds, such as sugars. This process is known as carbon fixation.
  • Phytoplankton, microscopic organisms found in aquatic ecosystems, only account for 1–2% of global primary producer biomass, yet contribute approximately 40% of global carbon fixation.
  • Phytoplankton are expected to become an important contributor in the efforts to mitigate carbon dioxide emissions worldwide.

Carbon fixation refers to the removal of inorganic carbon from the atmosphere by living organisms and its conversion into organic compounds. With the ongoing high level of carbon dioxide (CO2) emissions from human activities, there’s growing interest in offsetting emissions or achieving carbon neutrality by taking advantage of this process. For example, many initiatives offer to plant trees for a donation or action in order to help offset global carbon emissions, and increasing numbers of companies intend to mitigate the CO2 produced by their activities by planting trees. This seems like a sound solution — after all, forests account for over half of all carbon sequestration by terrestrial ecosystems. However, deforestation is another ongoing issue that might limit the impact made by tree-planting efforts.

Despite accounting for only 1–2% of global primary producer biomass, phytoplankton contribute 40% of global carbon capture and storage.

Between 2015 and 2020, an estimated 10 million hectares of forest were lost annually, only half of which were replanted. That isn’t to say that tree-planting efforts are pointless — any attempts to increase forest coverage are, ultimately, a benefit — but there are organisms other than trees capable of sequestering large amounts of carbon.

Photosynthetic phytoplankton

Just as plants form the basis of the terrestrial food web, phytoplankton are the main primary producers in the ocean. Phytoplankton are a conglomeration of various microscopic organisms, including bacteria and algae, that use sunlight as a source of energy, with the necessary cellular structures for photosynthesis. As the main driver of photosynthesis is light from the sun, they are mainly found in the upper layers of the ocean, where light penetrates. As is the case with plants, phytoplankton convert CO2 from the atmosphere into sugars. Then, they are eaten by zooplankton — microscopic organisms that gain their energy from consuming other zooplankton or phytoplankton, as well as small fish and crustaceans. These consumers are then eaten by larger animals, such as larger fish and baleen whales, which are predated upon by the top predators in the ocean, ie, toothed whales, sharks, and seals. Through predation, the CO2 captured by the phytoplankton at the beginning of the food web remains in the ocean. Additionally, any phytoplankton that are not predated upon eventually die and sink to the bottom of the ocean, taking that carbon with them. Despite accounting for only 1–2% of global primary producer biomass, phytoplankton contribute 40% of global carbon capture and storage.

The effect of climate change on carbon cycling in the ocean is currently unclear. It’s expected that rising temperatures will disrupt oceanic circulation and thus the transport of nutrients essential for growth, but there’s growing evidence that, despite warming temperatures, some phytoplankton species may be able to increase the amount of carbon they capture. Additionally, some plankton have the ability to both photosynthesise and consume other organisms — it’s believed that these types of organisms may thrive as the ocean becomes more unpredictable, since they can capture carbon while using another nutritional mode if necessary.

Amazing algae

As the availability of land for carbon fixation decreases due to ongoing urbanisation and deforestation continues, scientists have turned their attention to algae. In addition to natural processes, ongoing research is exploring the option of using technology to mass-capture carbon using algae.

It’s believed that growing algae in tanks could capture large amounts of CO2 from the atmosphere, while occupying a much smaller area than that required by terrestrial plants. Additionally, algal biomass can be used to generate useful products, such as biofuel. As such, it is expected that algae farming will make a significant contribution to decreasing atmospheric CO2 emissions in the future.

Rachel Herbert-Goddard is a freelance writer based in South Wales, with an interest in all things marine.

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