Barnacles which are related to crabs and lobsters, tend to live in shallow water. They attach themselves to any hard surface; Among those surfaces they attach themselves to the hulls of any boat.
The barnacles that are attached to the boats damage them, and cause another problem that the biofouling used in those boats are much more after the barnacles are attached than before.
The U.S. Naval Academy estimates that biofouling creates enough hull-drag to increase the Navy’s petroleum bill by about $250 million every year. For millennia, copper has been used to keep marine life at bay; the Greeks and Romans used copper nails for this reason. The Navy uses it too, mixing powdered copper into boat paint. But as the paint wears, copper seeps into the water, where it has been shown to harm salmon and oysters. And as the paint thins, the barnacles return.
Medetomidine, a chemical that activates the octopamine receptors (similar to adrenaline receptors) in barnacle larvae, causing them to flee. Barnacle larvae are free-floating and harden only after they have attached to a surface. Researchers at the University of Gothenburg in Sweden mixed small Plexiglas capsules filled with medetomidine into boat paint, young barnacles were scared away, and the hulls remained pristine. At high levels, medetomidine can lighten the color of fish scales, making them more vulnerable to predators. But the capsules ensure that the chemical is released slowly, so it lasts longer and minimizes environmental damage.