The chance rescue of a deep-sea octopus from a line trap gave researchers at Scripps Institution of Oceanography at UC San Diego the opportunity to make unprecedented observations.
This particular North Pacific big-eye octopus (Octopus californicus) was recovered from a trap set from 200m-250m depth near La Jolla, California. Deep-sea specimens are notoriously difficult to keep alive in captivity, yet this octopus went on to lay fertilized eggs at the Scripps Experimental Aquarium facility.
For the first time, researchers observed as baby octopuses from a deep-ocean species developed and hatched and witnessed the octopus’s behaviour before and after she laid the eggs.
“Even though this species was discovered over a century ago, we didn’t know how long incubation would take or anything about its early life history. They’ve rarely been raised in captivity and there were no other known records of fertilized eggs,” said Adi Khen, a Scripps Oceanography graduate student and lead author of the study, which was released in early November in the journal Ecology and Evolution.
Though the cephalopod life cycle is not part of Khen’s core research – she studies the health of coral reef communities and how they respond to heat stress – she and colleagues realized the unique opportunity to document this process.
Eye spots were noticed within the octopus eggs after four months, indicating that they were fertilized. The female octopus had apparently mated in the wild and stored the sperm for as long as a month. That trait has been observed in other cephalopod species.
The female octopus demonstrated typical octopus maternal behaviour of constantly guarding the eggs, cleaning them with her suckers and blowing water on them.
Khen said the ten-month development period until all eggs finally hatched was a victory for science, but bittersweet nonetheless. After five months caring for the eggs, the female octopus was found dead after having climbed out of the tank overnight. Perhaps significantly, there had only been two previous occasions in which captive octopuses left the open tanks in the Scripps Experimental Aquarium facility where the octopus was kept. In both cases, they were brooding females.
At that point, Khen and colleagues took over caring for the eggs, aerating them with a turkey baster to simulate movement by the female’s arms and to prevent bacterial or fungal growth. They also set up a webcam to monitor the eggs remotely. It is inevitable for brooding octopuses to die when their eggs hatch; partly because they stop eating while watching over the eggs, but also because they are naturally programmed to die after a short time due to their optic gland, which controls reproduction and aging. This octopus, however, had been fed regularly.
“I’d like to believe she trusted us and thought we had it handled,” Khen said.
The eggs hatched over the course of two and a half months. None in the first group survived, possibly from prematurity, but later hatchlings did, being developed enough to eat the amphipods, frozen krill and fish fed to them. Several were donated to aquaria throughout California. The specimens that did not survive were frozen, preserved and permanently housed in the Benthic Invertebrate Collection at Scripps Oceanography.
“Despite their loss, they can still contribute to science,” Khen said.
Photo credit: Adi Khen
