By Matt Walker
Editor, Earth News
A jumbo squid emerges from the murky depths
Jumbo squid have developed a novel strategy that allows them to maintain a super-charged predatory lifestyle.
After spending the night hunting fish near the surface, the squid dive into deeper cold waters to rest.
To survive in these depths, where little oxygen remains, the squid shut down their metabolism, before cranking it up to rise and resume their hunt.
The discovery explains for the first time how jumbo squid survive in these deep water dead zones.
Details are published in the journal Progress in Oceanography.
Jumbo squid, also known as Humboldt squid, are large, powerful predators measuring up to 2m long and 50kg in mass.
Living in the eastern Pacific, the squid are calculated to consume more than four million tonnes of food per year, primarily fish known as myctophids.
The squid hunt and move using jet propulsion, which makes them highly energetic animals.
But that has raised questions over how the squid maintain their lifestyle.
It was known that each day the squid migrate down into the ocean, descending hundreds of metres, before rising again to hunt fish nearer the surface at night.
Within these intermediate depths, however, are pronounced zones of low oxygen, known as oxygen minimum layers, which can extend for hundreds of metres deep and several kilometres wide.
"Jumbo squid display oxygen consumption rates that are among the highest in the oceans. This high energy demand reflects the low efficiency of jet propulsion."
Jumbo squid are fished in huge numbers
"So the question is how can they survive in these deep, cold and oxygen depleted zones?" asks Dr Rui Rosa from the Center of Oceanography, University of Lisbon in Portugal.
The answer, scientists have discovered, is that these large squid shut down their bodies, the first time squid have been shown to respond in this way.
Dr Rosa undertook a study into jumbo squid physiology with Dr Brad Seibel from the University of Rhode Island, Kingston, US.
Together, they captured 71 jumbo squid from the wild and tested their oxygen demands in sea water aquaria held onboard a research ship.
The researchers measured how the squid reacted to water containing high and low amounts of oxygen, and colder temperatures, mimicking conditions found at the surface and in the oceanic dead zones.
When placed in low oxygen water, the squid shut down their metabolism by over 80 per cent.
This extraordinary ability allows the jumbo squid to exploit habitats that other competing large marine predators cannot reach, say the researchers.
It also allows the squid to stay out of the reach of predators that might prey on the squid themselves, as top fish predators such as marlin, tuna and sailfish cannot descend into these cold, oxygen depleted zones.