Sea urchins, parrot fish, and limpets and chitons (both mollusks) feed on coralline algae. They also feed on chitons, limpets, snails, barnacles, echinoids, and even decapod crustacea. They prey on several kinds of sea organisms including barnacles, gastropods, bivalves and limpets. "O. bimaculatus" is known to prey on crustaceans, snails, chitons, limpets, and bivalves. Littoral, growing on rock, pebbles, limpets and barnacles. Starfish are abundant, as are sea urchins and limpets. Morphologically, many mollusks (such as limpets and chitons) have low-profile, hydrodynamic shells. There are some enoplan species known to feed upon barnacles, limpets, and polychaetes. The bacterial mats provide nourishment for mussels, clams, limpets and sea snails. Barnacles are displaced by limpets and mussels, which compete for space. Gastropod shells that are not spirally coiled (for example shells of limpets) have no columella. Its prey ranges in size from tiny limpets and crabs to giant octopuses. True limpets in the family Patellidae live on hard surfaces in the intertidal zone. People are also very keen on the mussels and limpets collected on the island's coasts. Shore gathering of limpets, winkles and ormers were permitted in certain places at certain times.