Infaunal

Infaunal is a term used in marine biology and freshwater ecology to describe animals that live within the substrate of a body of water, most commonly within the sediments of the seafloor or riverbeds. Infauna occupy burrows, tubes, or the pore spaces between sediment grains, in contrast to epifauna, which live on the surface of the substrate, and pelagic species that inhabit the water column.

Groups commonly described as infaunal include polychaete worms, bivalve mollusks such as clams and cockles, burrowing crustaceans, and certain echinoderms. Infauna are often categorized by size into macroinfauna (larger organisms) and meiofauna (smaller organisms that live within sediment interstices).

Infaunal organisms influence sediment structure and chemistry through bioturbation and bioirrigation: they churn the sediment, change porosity, increase oxygen penetration, and alter the distribution of organic matter. These processes affect nutrient cycling, carbon burial, and the habitat quality for other benthic life, and can contribute to sediment stabilization or destabilization depending on species and density.

Infaunal communities are sensitive indicators of environmental conditions, responding to pollution, oxygen availability, salinity, and organic enrichment. They are commonly sampled with cores or grabs, followed by washing, sieving, and taxonomic analysis for ecological assessment.