Sea turtle
Sea turtle shells are an ideal habitat for adult barnacles for three reasons. Sea turtles tend to live long lives, greater than 70 years, so barnacles do not have to worry about host death. However, mortality in sea turtle barnacles is often driven by their host shedding the scutes on which the barnacle is attached, rather than the death of the sea turtle itself. Secondly, barnacles are suspension feeders. Sea turtles spend most of their lives swimming and following ocean currents and as water runs along the back of the sea turtle's shell it passes over the barnacles, providing an almost constant water flow and influx of food particles. Lastly, the long distances and inter-ocean travel these sea turtles swim throughout their lifetime offers the perfect mechanism for dispersal of barnacle larvae. Allowing the barnacle species to distribute themselves throughout global waters is a high fitness advantage of this commensalism.