Microbenthic

Microbenthic refers to microscopic organisms that inhabit and form communities on or within the uppermost layers of sediment in aquatic environments. These organisms live at the sediment–water interface or within the pore waters and are typically smaller than the organisms characteristic of the macro- or meiobenthos. The microbenthic component of benthic ecosystems includes bacteria and archaea, microalgae such as diatoms and cyanobacteria, fungi, and protozoa (including ciliates and flagellates); in some environments, tiny metazoans and foraminifera are also considered part of the microbenthic assemblage.

Ecology and functions of the microbenthic community include contributions to primary production in sediments through photosynthesis by microalgae in the photic zone, and to organic matter decomposition and nutrient cycling via bacterial and fungal metabolism. They influence sediment stability, pore-water chemistry, and fluxes of carbon, nitrogen, and phosphorus across the sediment–water interface. In many systems they form the base of benthic food webs and respond rapidly to changes in sediment texture, oxygen availability, salinity, and pollutant levels.

Distribution and study of microbenthic organisms span marine, freshwater, and estuarine sediments worldwide, from shallow littoral zones to deep basins and polar regions. Sampling is typically done with sediment cores or grabs, and analyses employ microscopy, pigment measurements (as proxies for algal biomass), and molecular methods such as DNA sequencing to characterize community composition. Common metrics include abundance, biomass, and species richness, as well as functional indicators like rates of photosynthesis or mineralization.