Tiny ocean microbes called Prochlorococcus, thought to be climate survivors, may struggle as seas warm. These cyanobacteria drive 5% of Earth’s photosynthesis and underpin much of the marine food web. They thrive only within a narrow temperature range. Warming oceans could slash their populations by up to 50% in tropical waters.
https://www.ocean.washington.edu/story/Ocean_Microbe_Important_to_Climate_Change