Protists form the foundation of aquatic food webs and drive global nutrient cycles, yet distinguishing which species photosynthesize, graze or do both remains a major challenge because most are uncultivable and community surveys seldom resolve species‐level traits. We developed a field grazing‐scPCR framework that integrates short‐term grazing assays, single‐cell microscopy and 18S rRNA sequencing to link morphology, fluoresce...