Beyond the bottle: exposing the identity-rate gap in microzooplankton ecology.

Microzooplankton ecology was transformed by the dilution method, which made grazing measurable in natural plankton communities and established protistan grazers as major consumers of marine primary production. Four decades later, the field faces a different challenge. Automated imaging, metabarcoding, meta-omics and machine-learning tools increasingly resolve plankton identity, diversity and spatial structure, but grazer-resolved rates of ingestion, growth, prey selectivity, mortality and carbon transfer remain much harder to measure. This creates an identity-rate gap: community structure is becoming easier to describe than ecological function. The gap should not be reduced to a contrast between one classical method and modern identity tools; it reflects a broader difficulty of pairing organisms, prey, rates and environmental context within the same inference framework. Dilution experiments and related rate approaches remain indispensable, but their interpretation depends on assumptions about prey growth, grazer responses, nutrient limitation, mixoplankton behavior and bottle effects. Preserved samples also remain central to biomass estimates, although fixation and storage distort protists in taxon-specific ways. I argue that the next phase of microzooplankton ecology should not abandon classical incubations, but make them identity-aware, preservation-aware and model-facing through tiered datasets that separate bulk prey mortality, prey-resolved rates, targeted grazer-prey links and model-facing trait constraints.