Micrograzing

Micrograzing refers to the consumption of microorganisms by small grazers, typically protists and other microzooplankton, in aquatic and soil environments. It encompasses grazing on bacteria, small algae, and detrital particles by organisms such as ciliates, flagellates, and rotifers. Micrograzing is a key component of the microbial food web and helps link microbial production to higher trophic levels.

Common micrograzers include heterotrophic and mixotrophic protists like ciliates and oligotrichs, as well as naked and lorica-bearing flagellates. These organisms feed by phagocytosing prey or filtering particles, and some can switch between heterotrophy and photosynthesis (mixotrophy). Feeding is often size-selective and influenced by prey abundance, nutrient availability, temperature, and the physical properties of the medium.

Ecological role: Micrograzing regulates bacterial and small algal populations, shapes community composition, and drives the microbial loop, wherein carbon and nutrients flow from dissolved pools and microbial detritus into grazer biomass and then to higher trophic levels. Excretion and egestion by micrograzers return nutrients to the environment and can promote production of dissolved organic matter that fuels bacterial growth. In marine and freshwater systems, micrograzing can help control algal blooms and influence carbon export in the short term.

Measurement and research: Grazing rates are estimated using approaches such as dilution experiments, ingestion assays with labeled prey, and microscopic or molecular analyses of prey removal. Understanding micrograzing is important for models of nutrient cycling, carbon flow, and ecosystem responses to environmental change, including eutrophication and climate-driven shifts in temperature and stratification.