Underwater camouflage is the set of methods of achieving crypsis, avoidance of observation—that allows otherwise visible aquatic organism to remain unnoticed by other organisms such as predators or prey, and also aids predators in capturing their prey.
Three main camouflage methods predominate in water: transparency, reflection, and counterillumination. Transparency and reflectivity are most important in the top 100 metres of the ocean; counterillumination is the main method from 100 metres down to 1000 metres; while camouflage becomes less important in the dark waters below 1000 metres.
Camouflage in relatively shallow waters is more like terrestrial camouflage, where additional methods are used by many animals. Using color and shape changes, and sometimes adapting to threats with blinding speed, marine species use a variety of tricks to confuse and outsmart likely predators. Some marine animals also use camouflage to lie in wait for prey, which provides the hunters with the element of surprise and conserves valuable energy.
For example, self-decoration is employed by decorator crab, mimesis by animals such as the leafy sea dragons, countershading by many fish including sharks, distraction with eyespots by many fish; active camouflage, through ability to change colour rapidly in fish such as the flounder, and cephalopods including octopus, cuttlefish and squids.
The camouflage color or pattern can be inherited or acquired – many fish and some invertebrates are able to change color to match their surroundings. Other animals achieve camouflage by covering themselves, such as by burying in sand, or by attaching foreign objects to their body or shell.