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Intraspecific variation in diatoms has been shown to play a key role in species' responses to several important environmental factors such as light, salinity, temperature and nutrients. Furthermore, modelling efforts indicate that this variation within species extends bloom periods, and likely provides sufficient variability in competitive interactions between species under hydrographically variable conditions. The intraspecific variation most likely corresponds to optimal fitness in temporary microhabitats and may help to explain the paradox of the plankton. Here, we examine the implications of intraspecific variation for the ecology and success of diatoms in general and emphasize the potential implications for our understanding of carbon metabolism in these important organisms. Additionally, data from palaeoecological studies have the potential for evaluating genetic variation through past climate changes, going thousands of years back in time. We suggest pathways for future research including the adoption of multiple strains of individual species into studies of diatom carbon metabolism, to refine our understanding of the variation within and between species, and the inclusion of experimental evolution as a tool for understanding potential evolutionary responses of diatom carbon metabolism to climate change.This article is part of the themed issue 'The peculiar carbon metabolism in diatoms'., (© 2017 The Author(s).)

Because of their large population sizes and rapid cell division rates, marine microbes have, or can generate, ample variation to fuel evolution over a few weeks or months, and subsequently have the potential to evolve in response to global change. Here we measure evolution in the marine diatom Skeletonema marinoi evolved in a natural plankton community in CO2-enriched mesocosms deployed in situ. Mesocosm enclosures are typically used to study how the species composition and biogeochemistry of marine communities respond to environmental shifts, but have not been used for experimental evolution to date. Using this approach, we detect a large evolutionary response to CO2 enrichment in a focal marine diatom, where population growth rate increased by 1.3-fold in high CO2-evolved lineages. This study opens an exciting new possibility of carrying out in situ evolution experiments to understand how marine microbial communities evolve in response to environmental change.