Found via the RDFRS.
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".
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.