As fish and other rock pool animals feed on seaweed, crabs use the seaweed as a place to hide from predatory seabirds. As barnacles feed on microscopic plankton, dog whelks go hunting for barnacles. And after an oystercatcher eats a dog whelk, a hermit crab that’s grown too big for its shell, moves home into the empty shell left behind by the dog whelk! Step by step, readers will explore a rock pool habitat and discover how all the living things form an ecosystem and rely on each other for survival.