Glacier melting due to an increase in global climate temperatures
Most barnacles are filter feeders, sometimes known as “suspension feeders.” They feed on plankton and detritus (dead organic material), which they either sweep from the water into their mouths, using their fan-like feet, or they rely on the movement of the tide to bring the food to them.
Some animals (Arachnids, Crustaceans, Insects) don't have internal skeleton. They possess exoskeleton (chitinous skeleton).
It covers their body like a suit of armour, providing protection.