Unveiling the process driving the foundation of ocean ecosystems

Phytoplankton are the foundation of ocean ecosystems: like rainforests, they consume carbon from the atmosphere, form the foundation of the aquatic food web and are a vital player in impacting fish abundance and the global climate.

Understanding how these microscopic organisms grow is key to determining how much fish will be available to harvest, and how the climate will further change. However, incomplete knowledge about how phytoplankton respond to change hampers our ability to predict how they will be affected by climate change.

Researchers at the University of Liverpool, Dalhousie University, GEOMAR in Kiel, and the Scripps Institution of Oceanography have come up with a new mechanistic framework to look at phytoplankton growth in the ocean.

Phytoplankton growth can be thought of like a factory: materials come into the factory and are processed on assembly lines, forming the final product. For phytoplankton, this product is growing faster, and they rearrange their “cellular assembly lines” to grow fast.

Traditionally, it has been though that the scarcest resource in seawater sets phytoplankton growth, but this neglects an emerging biochemical understanding of cellular physiology.

Led by Scott McCain, a PhD candidate in the Biology Department at Dalhousie, the team specifically focused on the costs of these “cellular assembly lines” associated with different resources that go into making phytoplankton, rather than the amount of available materials. They then built a mathematical model of a phytoplankton to represent these costs, discovering new explanations for different phytoplankton behaviours.

Professor Alessandro Tagliabue, from the University of Liverpool’s Department of Earth, Ocean and Ecological Sciences, said: “You can think of the cell as a mini economy, we need to consider the sum of all internal costs to growth in a given environment to predict the ultimate growth rate.”

This fundamentally changes the way we look at phytoplankton growth and will lead to better predictions of how much phytoplankton grow in the ocean, and therefore also impact our predictions for fisheries and global climate change. Importantly, this model was able to be uniquely informed by a range of biochemical data usually not accounted for in these kinds of models.

Professor Tagliabue csaid: This work ‘brings forward a brand new paradigm by placing focus on what is going on inside the cell, rather than in seawater, which has been the previous focus. In doing so, our new approach brings together theory and observations as never before and provides an exciting future for better models.”

Ultimately this new understanding can be used to inform on the larger scale models and reduce uncertainty in how warming oceans will affect key ocean ecosystem services like net primary production, carbon sequestration and supporting the marine food supply.

The paper `Cellular costs underpin micronutrient limitation in phytoplankton’ (doi: 10.1126/sciadv.abg6501) is published  in the journal Scentce Advances.