Epibiont

An epibiont (from the Ancient Greek meaning "living on top of") is an organism that lives on the surface of another living organism.[1] An epibiont is, by definition, harmless to its host. In this sense, the interaction between the two organisms can be considered neutralistic or commensalistic; as opposed to being, for example, parasitic, in which case one organism benefits at the expense of the other, or mutualistic, in which both organisms obtain some explicit benefit from their coexistence). Examples of common epibionts are barnacles, remoras, and algae, many of which live on the surfaces of larger marine organisms such as whales, sharks, sea turtles, and mangrove trees. The host of the epibiont is typically referred to as the basibiont ("living underneath").[2]

The blowholes of a gray whale, with barnacle epibionts

The tabulate coral Aulopora attached to the brachiopod Strophodonta, from the Middle Devonian of Wisconsin

Although there is no direct effect of the epibiont to the host, there are often indirect effects resulting from this interaction and change in the surface of the host. This has been found to be especially important to marine organisms and aquatic ecosystems, as surface qualities do impact necessary ecological functions such as drag, radiation absorption, nutrient uptake, etc.[3]