One octopus species living in Antarctic waters is a blue blood - literally, say scientists who've discovered it uses a blue pigment in its blood to survive in sub-zero temperatures.
That may also help it survive higher temperatures associated with climate change, which could help explain why the octopus - Pareledone charcoti - is doing well in its frigid habitat while other animals there are not, the researchers say.
Ice-cold waters in the Antarctic region contain large amounts of dissolved oxygen, but it can be difficult for an animal to get it into their tissues because of lower oxygen diffusion and an increase in blood viscosity, scientists say.
The octopus's secret weapon is a blue oxygen transport protein known as haemocyanin, analogous to the haemoglobin that makes blood red in vertebrates, researchers report in the journal Frontiers in Zoology.
"This is the first study providing clear evidence that the octopods' blue blood pigment, haemocyanin, undergoes functional changes to improve the supply of oxygen to tissue at sub-zero temperatures," says study leader Michael Oellermann from the Alfred-Wegener Institute in Germany.
The haemocyanin in octopods is able to support oxygen supply in both cold and warm environments, he says.
Due to that ability to provide "improved oxygen supply by haemocyanin at higher temperatures, this octopod may be physiologically better equipped than Antarctic fishes to cope with global warming," he adds.
With a strong warming trend observed around the Antarctic Peninsula, Pareledone charcoti may benefit from its capacity to adapt its blood oxygen supply to more variable temperatures than other species, including Antarctic fish, might manage, he says.
"This is important because it highlights a very different response compared to Antarctic fish to the cold conditions in the Southern Ocean," he says.
Octopods possess three hearts and veins that can contract, working together to pump "haemolymph," enriched with haemocyanin, around their bodies.
The Antarctic octopus was found to have the greatest concentration of haemocyanin in its blood of any octopod species, the researchers say, at least 40 percent more than in species found in warmer oceans.
The researchers compared the Antarctic octopus with the Australian Octopus pallidus and the Mediterranean Eledone moschata.
At 10 degrees C the Antarctic species' haemocyanin displayed the potential to release much more oxygen, an average 76.7 percent, than the Australian species' 33 percent or the Mediterranean octopus's 29.8 percent, they found.