One moment they're there and the next, they're completely gone. That's what researchers have discovered in some species of deep ocean squid and octopus that can switch from becoming transparent to becoming deep red to blend into their environment.

Researchers from Duke University studied the two species that live in what is called the ocean's "twilight zone" about 600 and 1000 meters below the surface where the bright upper layers of the water blend into the darker depths of the sea. Both regions require different camouflage sets to protect animals from predators. In the brighter region, animals would need to be transparent to avoid detection while in the darker regions animals would need to be red or black to hide them from fish that hunt with biological searchlights.

In a study published in the journal Current Biology by Sönke Johnsen, a visual ecologist and Sarah Zylinski, a postdoctoral scientist, there is evidence that squid and octopus species have the unique ability to change their color to blend in both the lighter and darker regions of the sea.

"Being able to switch allows the cephalopods to optimize their camouflage to the optical conditions of that moment," Zylinski says. "This is why the rapidity of the response is of the essence."

Many shallow water octopuses, squid and other cephalopods have the ability to camouflage themselves but this is the first time that the ability was observed in creatures that lived deeper in the ocean. Zylinksi and Johnsen caught some deep-water cephalopods and tested their responses to bioluminescence light. When the researchers shone blue light on the two species, a Japatella heathi octopus and Onychoteuthis banksii squid, they immediately went from transparent to opaque red. The animals did not respond the same way to beams of red light, moving light, or other kinds of light disturbances.

Not all deep-sea cephalopods have the ability to switch their appearance from transparent to opaque, Zylinski said. Some species are very reflective while others create their own bioluminescence to match the ambient light.

Studying how these deep-water cephalopods use camouflage could help in building better nets that are invisible to the species of fish that fishermen want to catch. Studying transparency in animals has already helped scientists understand how human cataracts work.