Clownfish live in sea anemones which protect them from harm and they feed the sea anemone food scraps.
Octopuses live in cracks which they wedge their bodies into. Octopuses may also barricade the opening to their home with rocks, rubble and shells.
Crown of Thorns starfish live in coral reefs and feed on coral. Outbreaks can decimate coral reefs if the population of Crown of Thorns starfish is not controlled.
Parrotfish live in seagrass beds and coral reefs. They are a contributors to bio-erosion.