The marine phytoplankton include at least 9 major evolutionary lineages, but all share a highly conseved Photosystem II complex that drives oceanic productivity, while releasing oxygen as a byproduct.  Photosystem II is susceptible to photoinactivation.  Now, changing CO2, nutrients and oceanic temperatures are altering susceptibilities to photoinactivation, thereby changing the competitive interactions among phytoplankton, with complex potential consequences.