Infauna

Infauna are animals that live within the sediments of aquatic environments, from shallow shores to deep-sea basins. They occupy burrows, tubes, or simply the pore spaces between sediment grains. Unlike epifauna, which live on the seafloor surface, infauna dwell inside the substrate and interact extensively with the sediment and its microbial community.

Size-based categories are microfauna (<0.1 mm), meiofauna (0.1–1 mm), and macrofauna (>1 mm). Common infaunal groups include polychaete worms, bivalve mollusks, and burrowing crustaceans; also numerous nematodes, copepods, and ostracods among meiofauna; microscopic protozoa and foraminifera among microfauna.

Ecologically, infauna drive bioturbation and bioirrigation, mixing sediment layers and promoting exchange of gases and solutes between sediment and overlying water. They contribute to decomposition and nutrient cycling, affect sediment structure and stability, and provide habitat and food for higher trophic levels.

Infaunal communities respond to environmental conditions such as organic enrichment, sediment grain size, and oxygen availability, making them useful indicators of habitat health and anthropogenic impact. They are sampled by core sampling, grab samplers, or dredges; samples are processed to determine species composition, abundance, and biomass.

Taxonomic diversity and functional traits of infauna vary with depth, sediment type, and climate. Studying infauna informs ecology, paleoenvironments, and environmental monitoring.