Dead Squid Moms Are a Gift to the Ocean Floor

Animals living on the ocean floor, where it's too dark for anything to grow, have to wait for food to fall on them. Mostly this means they eat "marine snow," a steady drift of tiny life forms and detritus from the ocean's surface. But robotic expeditions off the coast of Mexico have revealed what might be another major dining option on the ocean floor: dead squid moms. The Monterey Bay Aquarium Research Institute (MBARI) sent one of its remotely operated vehicles to explore deep basins in the Gulf of California between 2012 and 2015. With its cameras, the robotic submarine captured a surprising number of squid carcasses. Eleven out of 80 dives came across sites where squid had fallen to the ocean floor. In the videos, researchers saw not just squid bodies, but crumpled black sheets that had fallen with the squid, as in the photo above. These were the remains of squid egg sheets. Certain squid called gonatids carry these sheets—embedded with developing embryos, and apparently darkened with ink—in their arms until their babies hatch. Gonatids, like other squid, have short life spans. Male and female squid both die after they've reproduced. Some types of female squid start to physically disintegrate while they're still making their eggs, then float to the surface and are eaten by birds after they've released the eggs. But in the Gulf of California, many squid moms appear to sink after their babies hatch, still clutching their egg sheets. The researchers also found squid egg sheets on the ocean floor without carcasses, and assumed these sheets fell with squid that had already been eaten. Between carcasses and empty egg sheets, the researchers saw the remains of 64 squid on these dives. They spotted sea stars, crabs, and other scavengers feasting on the carcasses—though the scientists note that these animals weren't as enthusiastic about eating the egg sheets, which may be "less palatable." Extrapolating to the whole region, the authors calculate that fallen squid may be a major and overlooked part of the ocean-floor food chain. As climate change seems to be increasing squid populations, that means expired squid moms may be more and more on the menu. Image: MBARI