By VICTORIA GILL - BBC NEWS
Added: Thu, 10 Nov 2011 18:29:16 UTC

Scientists have discovered how two marine creatures are able to rapidly "switch" their colours - from transparent to reddish brown.

The species, an octopus and a squid, use their adaptable camouflage to cope with changing light conditions in the deep ocean.

The creatures' skins respond light that deep-sea predators produce to illuminate their prey.

The findings are reported in the journal Current Biology.

Sarah Zylinski and Sonke Johnsen from Duke University in North Carolina, US, carried out the research. They say this switchable camouflage allows the animals to hide more effectively in their uniquely gloomy marine environment.

When sunlight diffuses evenly through the water, it passes through transparent animals too, rendering them almost invisible. But, as Dr Zylinski explained, "transparent tissues are actually quite visible when you shine a light directly on them".

And this is exactly what many deep-ocean predators do.

Prof Michael Land, a biologist from the UK's University of Sussex explained that by a depth of 600m, sunlight fizzles out, and hiding becomes much trickier for prey animals. This is the depth at which the octopus Japetella heathi and the squid Onychoteuthis banksii live.

Prof Land told BBC Nature: "[At that depth], you have all these nasty fish that are trying to illuminate you, so it's best to be a dark colour."

These "nasty" predatory fish are equipped with light-producing organs that function as biological headlamps.

To cope with this, the two creatures the scientists examined have evolved a clever way to hide.

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TAGGED: BEHAVIOR, EVOLUTION