The ocean’s most abundant microbe is near its breaking point

Tiny ocean microbes called Prochlorococcus, once 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. A decade of research shows they thrive only within a narrow temperature range, and warming oceans could slash their populations by up to 50% in tropical waters.