After accidentally saving a female bigeye tuna last year, researchers at the Scripps Institution of Oceanography at UC San Diego in La Jolla had the opportunity to make some never-before-seen observations.
A study associated with the findings was published recently in the journal Ecology and evolution.
The North Pacific bigeye octopus (California octopus) was recovered from a shrimp trap set 200 to 250 meters (655 to 820 ft) deep near La Jolla in April 2021. In such cases, incidentally captured animals are sometimes taken to the experimental aquarium at SIO to be studied there.
“For this species in general, it’s difficult to study them because they live in the open ocean,” said Adi Khen, a Scripps graduate student in oceanography and lead author of the study. “It is difficult to observe them in their natural habitat.”
Because of this, she said, “we didn’t know anything about how long eggs take to develop and what their life cycle is.”
One day about a month after arriving at SIO, the octopus laid 200 eggs in the corner of its tank.
“We assumed they weren’t fertilized because we had her alone in the tank,” Khen said. “So how would she have mated?” But she began to keep them; she was very focused on the eggs. She would literally monitor them 24/7. She ate holding the eggs, slept holding the eggs.
The octopus would clean the eggs and blow water over them to prevent debris and bacteria from growing on them. “She was very dedicated,” Khen said.
About four months after the eggs were laid, the researchers noticed dots within them that indicated the eyes were developing, meaning the eggs had been fertilized.
“We thought what must have happened was that she mated in the wild, stored the sperm – which they’re known to do – and she used it to fertilize the eggs. that she laid in our aquarium, so she fertilized them herself during her captivity,” Khen said.
Jumping at the chance to study the process further, the researchers stepped up to help take care of the eggs, Khen said. “First, [the mother octopus] had covered it; she kept them and she still ate. But we also know that with octopuses, once they lay their eggs, their life is over. They only lay eggs once in their lifetime, and then shortly after they die.
Such was the case with Scripps.
After five months of caring for the eggs, the mother crawled out of the tank and died. Khen said it is common for mother octopuses to keep their eggs and not eat and thus starve to death. Others deal with changes in their internal processes that would be comparable to dementia in humans.
After the mother died, the researchers took care of the eggs.
“When I woke up in the morning, I checked them on a webcam connected to my phone,” Khen said. “When I arrived at the lab, I would watch the eggs and sometimes even use a turkey baster to squirt water over the eggs to clean them. I would watch how they develop. Shortly after the appearance eye spots, we began to see more of the body.
About eight months after the eggs were laid, the first ones hatched. These newborns, presumed premature, did not survive.
Two months later, others started to hatch and survived.
“So we learned that this species had a 10-month incubation period,” Khen said. “For this species, although it was discovered over a century ago, there is hardly any information about it, so we didn’t know. But now we have this observation.
“[The mother octopus’s] life has contributed to science; it will live thanks to science. And this discovery will forever be linked to La Jolla.
— Adi Khen, Scripps Institute of Oceanography
Hatchlings were fed amphipods, frozen krill and fish and grew to the point where they could be sent to aquariums across the country.
Khen said future scientific studies could refer to WIS observations and aquariums could learn more about how to care for obese North Pacific octopuses.
“Sometimes an aquarium gets an octopus as a bycatch, but until now there weren’t really any guidelines on how to keep or feed them,” Khen said. “And if an octopus lays eggs in captivity, an aquarium might assume they’re not fertilized. Now we know how long it takes for them to develop.
The study’s co-authors include Lillian McCormick, Christine Steinke, Greg Rouse and Phil Zerofski, all of Scripps Oceanography.
Khen said she felt connected to mother octopus, eggs and newborns.
“They looked as much like my babies as they did hers,” she said. “[The mother octopus’s] life has contributed to science; it will live thanks to science. And this discovery will forever be linked to La Jolla. ◆