Whales and barnacles share a relationship called commensalism. The barnacles benefit the most, hitching a ride on whales for protection and food. Meanwhile, they don't harm the whales. It's a one-sided, harmless free ride.

The barnacles are just along for the ride. They don't harm the whales or feed on the whales, like true parasites do. Barnacles don't serve any obvious advantage to the whales, but they give helpful lice a place to hang onto the whale without getting washed away by water.