epibiont

An epibiont is an organism that lives on the surface of another living organism, which is referred to as the basibiont. Epibionts are defined by their external association rather than by feeding on the host; they can be commensal, mutualistic, or neutral, and in some cases may become burdensome if they impose a cost on the host.

Epibionts occur across ecosystems and include a range of organisms such as algae, bryozoans, barnacles, diatoms, and other small invertebrates. In marine environments, epibionts commonly attach to the bodies of whales and sea turtles, to shells of mollusks, or to submerged plants and sessile invertebrates. Attachment methods vary and may involve specialized structures, cementation, byssal threads, or elaborate exoskeletons.

The presence of epibionts can influence host ecology in several ways. They may alter surface roughness, hydrodynamics, or camouflage and can provide microhabitats for additional organisms. Conversely, heavy or persistent epibiont colonization may affect the host’s movement, energy balance, or susceptibility to fouling or infection. Because relationships range from neutral to beneficial or detrimental, the ecological role of epibionts is context-dependent and an active area of study.

Researchers distinguish epibionts from endobionts, which live inside the host, and from ectoparasites, which live on the surface and obtain nutrients from the host. Studying epibionts involves field surveys, microscopy, and molecular methods to identify species and assess their interactions with hosts.