Washington:
Researchers have observed a deep-sea octopus protecting and tending its eggs for four-and-a-half years until they hatched - the longest-known egg-brooding period for any animal.
Throughout the four-and-a-half years, the female kept the eggs clean and guarded them from predators, said researchers at the University of Rhode Island and the Monterey Bay Aquarium Research Institute in the US.
This feat represents an evolutionary balancing act between the benefits to the young octopuses of having plenty of time to develop within their eggs, and their mother's ability to survive for years with little or no food.
Every few months for the last 25 years, a team of Monterey Bay researchers led by Bruce Robison has performed surveys of deep-sea animals at a research site in the depths of Monterey Canyon that they call Midwater 1.
In May 2007, during one of these surveys, the researchers discovered a female octopus clinging to a rocky ledge just above the floor of the canyon, about 4,600 feet below the ocean surface.
The octopus, a species known as Graneledone boreopacifica, had not been in this location during their previous dive at this site in April.
Over the next four-and-a-half years, the researchers dove at this same site 18 times. Each time, they found the same octopus, which they could identify by her distinctive scars, in the same place.
As the years passed, her translucent eggs grew larger and the researchers could see young octopuses developing inside. Over the same period, the female gradually lost weight and her skin became loose and pale.
The researchers never saw the female leave her eggs or eat anything. She did not even show interest in small crabs and shrimp that crawled or swam by, as long as they did not bother her eggs.
The last time the researchers saw the brooding octopus was in September 2011. When they returned one month later, they found that the female was gone.
In a paper published in the journal PLOS ONE, researchers wrote that "the rock face she had occupied held the tattered remnants of empty egg capsules."
After counting the remnants of the egg capsules, the researchers estimated that the female octopus had been brooding about 160 eggs.
Because the young octopus spend so much time in their eggs, by the time they hatch they are fully capable of surviving on their own and hunting for small prey.
The newborns of G boreopacifica are larger and better developed than the hatchlings of any other octopus or squid.
This research suggests that, in addition to setting records for the longest brooding time of any animal, Graneledone boreopacifica may be one of the longest lived cephalopods (a group that includes octopuses, squids, and their relatives).
Most shallow-water octopuses and squids live just a year or two.
