Modelling the effects of chromatic adaptation on phytoplankton community structure in the oligotrophic ocean

We explored the role of chromatic adaptation in shaping vertical phytoplankton community structures using a trait-based ecosystem model. The model included 1000 ‘phytoplankton types’ and was applied to the oligotrophic South Atlantic Gyre in a 1dimensional framework, where ‘phytoplankton types’ refers to the model phytoplankton that were stochastically assigned unique physiological characteristics. The model incorporates multi-spectral optics and light absorption properties for the different phytoplankton. The model successfully reproduced observed vertical gradients in the nitrate, bulk phytoplankton properties and community structure. Model phytoplankton types with Synechococcus-like spectral light absorption properties were outcompeted at depth, where eukaryote-like spectral properties were advantageous. In contrast, photoinhibition was important for vertical separation of high-light and low-light Prochlorococcus model analogues. In addition, temperature dependence was important for selection of phytoplankton types on the temperature gradient. The fittest, or successful, phytoplankton types were characterised by combinations of simultaneously optimal traits that suited them to a particular depth in the water column, reflecting the view that phytoplankton have co-evolved multiple traits that are advantageous in a particular environmental condition or niche.