Common octopus (Octopus vulgaris) hunting on the sea floor. A grouper fish (lower right) is waiting for prey that might escape. The common octopus is a nocturnal predator that hunts fish, crustaceans and bivalves. It is found worldwide in both temperate and tropical oceans to a depth of 180 metres. Like all octopi, the common octopus can change colour according to its surroundings by dilating or contracting pigment cells called chromatophores. This acts as a form of camouflage from predators. Photographed off Bonaire island, Netherlands Antilles, Caribbean.