Image copyright MBARI Image caption The cephalopod super-mum refused food and warded off predators for a record-breaking 53 months

For four years and five months, she clung to the rock and guarded her eggs.

In a feat that surely made good use of all eight arms, an octopus revealed a new secret of deep sea life when ecologists observed her record-breaking behaviour from a robotic submarine.

This doubles the longest brooding time ever seen in the animal kingdom, giving embryos time to develop in the cold.

The discovery, published in the journal PLOS One, was made in a canyon 1.4km beneath the Pacific, off California.

Media playback is unsupported on your device Media caption Marine biologist Kerry Perkins discussing the octopus on the Today programme

Dr Bruce Robison led the research at the Monterey Bay Aquarium Research Institute (MBARI). He told BBC News his team had stumbled upon the plucky mother in the days before she settled down and glued her eggs to the rock face.

She was heading, slowly, for a known brooding site.

By looking at characteristic scars in one of her eight armpits, the team identified the same octopus on the next dive, one month later.

Cheer squad

It got to be like a sports team we were rooting for - we wanted her to survive and to succeed Dr Bruce Robison, Monterey Bay Aquarium Research Institute

"The first time that we dropped back down... and realised that she had gone up and laid a clutch of eggs, it was very exciting," Dr Robison said. "We knew that we had the beginning."

"No-one had ever had the good fortune to come upon the beginning of a brooding period."

That was May 2007 - Tony Blair was still in office and the world had only seen two Shrek movies.

For the next four and a half years, the team paid the devoted cephalopod 18 more visits, thanks to multimillion-dollar remote diving vehicles equipped with cameras, robotic arms, and laser lights to make physical measurements.

Image copyright MBARI Image caption Scientists first spotted the octopus heading for a brooding site on the rocks of the Monterey Canyon

"Each time we went down it was more of a surprise," Dr Robison said, "because we found her there again and again and again, past the point that anybody expected she'd persist.

"It got to be like a sports team we were rooting for. We wanted her to survive and to succeed."

Octopus and eggs were all still firmly in place in September 2011. By October, the same month that David Cameron urged his government to support same sex marriage and the first Puss in Boots spin-off landed, she had disappeared.

Empty egg cases littered the scene of her encampment.

Image copyright MBARI Image caption After four years and five months, only empty egg cases were left behind

Four-year fast?

The octopus probably died shortly after completing her vigil, according to Dr Robison. The brooding period typically takes up the final quarter of a female octopus's life.

"She has only one job once those eggs are deposited," he said.

He added she quite possibly ate nothing for the whole 53 months.

"Everything we know suggests she probably didn't eat," Dr Robison said. Most octopuses do not feed while brooding, he explained, and in countless dives his team had "never seen a clutch of eggs untended".

The only time the cameras saw this particular devoted mother pay any attention to the crabs or shrimps that strayed nearby - normally a square meal for an octopus - was when she batted them away from her 150 precious eggs.

Even when the team used one of the submarine's appendages to offer her a snack, they were resolutely ignored.

Kerry Perkins, an aquarist at the Sea Life aquarium in Brighton, said a four-year fast was a possibility, but noted that the octopus may have got nutrients from unlaid eggs or very occasional, unobserved titbits.

Image copyright MBARI Image caption The octopus tended her 160 eggs at a depth of 1.4km, keeping dirt away and flushing them with fresh water

"They're exceptionally good mothers," she said. "It is very, very cold water and they're not moving much, so their metabolic rate would be pretty low - but still, you'd think in four and a half years you'd probably have to have a snack at some point."

Eclipsed shrimp

Ms Perkins said she was "quite amazed" by the findings, which contribute to our still very rudimentary understanding of these deep-sea dwellers.

"They're still very much the aliens of the sea."

Dr Robison believes the icy temperature at these depths - about 3C - is what governs the extraordinary brooding routine.

Image copyright Dante Fenolio / SPL Image caption The previous brooding record was held by a giant red shrimp, which protects its eggs for 20 months

"The low temperature slows everything down," he said. A low metabolism allows the mother to survive on little or no food, while she protects the eggs and flushes water over them, keeping their oxygen supply up as they gradually develop.

The previous record for the longest known brooding time was 20 months, and belonged to a giant red shrimp.