Equipped with a powerful beak, sucker-packed tentacles, and arms lined with razor-sharp claws, the colossal squid (pictures) likely inspired legends of terrible sea monsters, including the ship-wrestling kraken.
But the squid's titanic reputation is slowly being deflated, thanks in part to a new study that says the creature is no more than a sluggish, gelatinous drifter.
The first study of the colossal squid's metabolic system shows that the squid's energy demands likely dictate a slow, aimless existence. The findings match with the initial conclusions of scientists who dissected a captured squid in 2008.
"We already knew it was a kind of gelatinous, soft animal," said marine biologist Rui Rosa of the University of Lisbon in Portugal, who led the study team.
The new data show "not an active or a fearsome predator, but one that has a really slow pace of life."
"Monster" Squid Ambushes Prey
Colossal squid are the world's largest invertebrates, or animals without backbones. The squid are shrouded in mystery: Colossal squid live in Antarctic waters at depths of about 6,560 feet (2,000 meters), and the elusive animals have never been observed alive in the wild.
Investigations of a 30-foot-long (10-meter-long) adult colossal squid caught accidentally off Antarctica in 2007 have been providing scientists with some of their first clues about the deep-sea giants. (See "Colossal Squid Has Glowing 'Cloaking Device,' Huge Eyes.")
For their new study, Rosa and colleagues looked at the physiologies and lifestyles of smaller, related squid species that also live in cold waters.
After scaling up the findings to match the colossal squid's size, the scientists concluded that the animal has a relatively low metabolic rate—in other words, colossal squid take a long time to convert nutrients from their food into energy.
This finding—plus the squid's cold blood and dark, icy home—implies that the colossal squid has generally slow movements and very low food requirements.
The team thinks the colossal squid ekes out an existence as a "sit and float" predator, grabbing the occasional passing fish, or by lying in ambush.
In fact, an 11-pound (5-kilogram) toothfish—known to be a typical meal for colossal squid—could sustain a 1,100-pound (500-kilogram) adult for 200 days, the study team estimates.
"It doesn't really have to consume much prey to maintain its way of life," Rosa said.
Overall, the squid's energy requirements are 300 to 600 times lower than those of warm-blooded whales, the other top predators in Antarctic waters.
And since the squid probably doesn't actively hunt, Rosa added, its dinner plate-size eyes are likely an adaptation for avoiding predators, such as sperm whales and sleeper sharks.
The colossal squid findings were published online last month in the Journal of the Marine Biological Association of the United Kingdom.