The role of pigments in phytoplankton biogeography and evolution

The ocean is home to tiny single celled plants, called phytoplankton, which form the base of the marine food chain. Despite their tiny size, the ocean's phytoplankton perform as much photosynthesis in a year as all the plants on land. There are thousands of different species of phytoplankton and each have unique characteristics, or traits, that mean they are particularly well suited to living in certain ocean conditions. It is important to understand why different phytoplankton species flourish in some parts of the ocean and not others. Some species are particularly important for sustaining fish stocks, and some are toxic to marine mammals and even humans. Also, since each species has different properties that affect how fast it grows and how likely it is to sink, they can have a different impact on the amount of carbon dioxide removed from the atmosphere and locked up in the deep ocean. An improved understanding of the distribution of phytoplankton species in the ocean will therefore enable us to predict how marine ecosystems might change in the future, and ultimately how phytoplankton may impact climate change. Unlike land plants, phytoplankton are obviously never short of water, but they often have to compete with one another for nutrients and light to survive. Each species contains a unique combination of pigments, which absorb the light needed for photosynthesis. The pigments absorb different colours, or wavelengths, of light. Since the wavelengths of available light vary throughout the oceans, phytoplankton species may be particularly well-suited to particular regions because of the wavelengths of light they can absorb. Pigments also need to be 'built' by the phytoplankton as they grow and each type of pigment requires a different amount of resources including carbon and nutrients (such a nitrogen and iron). Subsequently the kinds of pigments contained within different phytoplankton species not only influence the amount of light that they can absorb, but also the amount of nutrients they need to grow. In this study, I will develop and use mathematical models to explore how the pigment combinations of different phytoplankton species affect where they grow in the ocean. In addition to increasing our understanding of the factors influencing phytoplankton distributions, the models will enable us to further investigate interactions between ocean biology and global change.