The argonauts are a group of octopuses unlike any other. The females secrete a thin, white, brittle shell called the paper nautilus. Nestled with their arms tucked inside this beautiful, translucent home, they drift through the open ocean while other octopus species crawl along the sea floor. The shell is often described as an egg-case, but octopus specialists Julian Finn and Mark Norman have discovered that it has another function – it’s an organic ballast tank.
An argonaut uses its shell to trap air from the surface and dives to a depth where the encased gas perfectly counteracts its own weight, allowing it to bob effortlessly without rising or sinking. Finn and Norman filmed and photographed live animals in the act of trapping their air bubbles, solving a mystery that has been debated for millennia.
Octopuses are masters of camouflage that can change their shape, colour and texture to perfectly blend into their environment. But the soft bodies that make them such excellent con artists also make them incredibly vulnerable, should they be spotted. Some species have solved that problem with their fierce intellect, which allows them to make use of other materials that are much harder. The veined octopus, for example, dons a suit of armour made of coconut shells.
The veined octopus (Amphioctus marginatus) lives in sandy, exposed habitats that have little in the way of cover. To protect itself, it hides among the hollow husks of coconuts. It even carries its armour around with it, tucking the shell under its body, sitting on it like a bowl, and moving around on tip-tentacles.
The giant cephalopods (squids and octopuses) of the deep sea have captured the imagination for centuries. But despite our fascination with these creatures, they are still enigmas, their behaviour illuminated only by the occasional lucky video or the presence of scars on animals they fight with. For many species, including the famous giant squid, we still know relatively little about what they eat and what position they occupy in their ecosystems.
Yves Cherel from the Centre d’Etudes Biologiques de Chize has some new answers about the behaviour of deep-sea cephalopods and they came from a most unorthodox technique– he studied remains recovered from the stomachs of dead sperm whales.
It’s clear that sperm whales feed on squid and octopuses. Sucker-shaped scars along the backs of some individuals have led people to picture titanic battles between the whales and their giant prey. Once eaten, the cephalopods’ soft bodies are easily digested, but they also have hard, parrot-like beaks that aren’t easily broken down.
By looking in the stomachs of three sperm whales stranded in the Bay of Biscay, Cherel recovered hundreds of beaks from 19 separate species – 17 squids including the giant squid, the seven-arm octopus (the largest in the world) and the bizarre vampire squid. Together, these species represent a decent spread of the full diversity of deep-sea cephalopods.