All octopi live in saltwater, marine environments. These animals live in shallow waters and are primarily bottom-dwellers, meaning they nest and forage at the bottom of the ocean. However, some octopus species will swim over the ocean floor to catch currents for moving from one site to another. For nesting, an octopus will find a sheltered area -- known as an octopus lair -- and lay eggs in this environment. Octopus lairs are usually in coral reefs, rocks or tall seagrass beds.
An octopus will use its anatomy and environment when defending itself from predators. Octopus skin has a network of pigmented cells and specialized muscles, which allow it to blend in with rocks and coral reefs on the ocean floor. The cells and muscles enable the octopus to change its skin color and texture. If this tactic does not work, an octopus will squirt ink in the direction of the predator and take advantage of its mantle to swim away. An octopus' mantle is able to expel water, which accelerates the octopus' swimming speed.
As carnivorous creatures, an adult octopus' main dietary items are fish, gastropods and crabs. These marine animals are nocturnal hunters, meaning they are most active at night. When hunting for shelled crustaceans -- crabs and lobsters -- an octopus uses venomous saliva to kill its prey and its powerful beak is able to crack open a crustacean's shell. If its prey has a harder shell, such as a sea snail, octopus have a radula, which it uses to drill a hole in the snail's shell. Once they are through with their shelled prey, octopi create an octopus garden outside the lair; an octopus garden is a collection of empty crustacean and sea snail shells.
No octopus species are listed as endangered by the International Union for the Conservation of Nature or the Washington Convention. One major environmental concern for octopus is water degradation since these animals are sensitive to water pollution, according the Smithsonian National Zoological Park. Over-hunting is another conservation concern because octopi are popular restaurant dishes; approximately 10 percent of all cephalopod catches are octopi.