While the lives of squid are mysterious in many ways, one gruesome truth is that after mating comes death.
First the male dies. Next the female, after making a little pouch of eggs, begins to starve.
“She is unable to feed because the egg mass is in front of the mouth,” explains Henk-Jan Hoving, a deep sea biologist at Geomar Helmholtz Centre for Ocean Research in Kiel, Germany. “She probably gets energy from the breakdown of her own tissue, either from the liver or the mental tissue. This is how she stays alive, basically.”
Then, once the female is dead and the eggs have hatched, her body will often float to the ocean’s surface and get eaten by birds.
But for some species, it appears, the bodies sink. In a paper published recently in Proceedings of the Royal Society B, Dr. Hoving and colleagues at the Monterey Bay Aquarium Research Institute, where he was formerly a researcher, described happening upon the remains of 64 squid and squid egg cases during dives with a remotely operated vehicle or ROV in Mexico’s Gulf of California. If squid in other locations are also found to drift to the bottom like this, they may play a previously unidentified part in the ocean’s role as a storage place for carbon, which could have implications for the study of climate change.
Dr. Hoving recalls the 2012 trip when the researchers first realized they were seeing something interesting. “When we visited the bottom of one of the dives with the ROVs, we saw a dead squid and then another one,” he says. Video footage from other outings to the area also showed bodies, they later learned, and in 2015 they returned again, finding more squid carcasses scattered across the floor, some nearly 10,000 feet down.
While many dives showed no squid, others were thick with them, as well as crustaceans and sea stars contentedly feeding on some of the remains. Could mating, and thus the slow rain of corpses, be seasonal? We don’t know yet, says Dr. Hoving, but he and collaborators plan to conduct a more standardized survey in the future, perhaps using cameras stationed on the ocean bottom.
It’s a question that matters not just for our interest in the personal lives of squid, but also for understanding how the oceans, by far the world’s largest storage place of carbon, perform that role. The researchers now estimate that at least in parts of the Gulf of California, squid may add up to about 12 milligrams of carbon per square meter per day on the ocean floor. That is a significant amount, about half of what gets stored by the incessant fall of tiny plankton bodies at shallower, better studied depths.
Squid populations are presently exploding, researchers now know, perhaps because of warming oceans or because humans have depleted fish that prey on them. Understanding just how they contribute to the sequestering of carbon in the oceans will add important details to our picture of the planet.