Common Cuttlefish (Sepia officinalis): Facts and Camouflage

What does a common cuttlefish look like?

The common cuttlefish has a broad, slightly flattened oval body called the mantle. A narrow fin runs along each side of the mantle for almost its whole length, and by rippling these fins the cuttlefish can hover, creep forward or slide backward with great precision. For a fast escape it switches to jet propulsion, squirting water out through a flexible funnel called the siphon.

At the front, eight sucker-lined arms surround a hard, parrot-like beak. Two longer feeding tentacles, each ending in a club armed with toothed suckers, stay tucked away in pockets under the eyes until the moment of attack. The large eyes have a distinctive W-shaped pupil, which may help balance the bright light from above with the dimmer light below.

Resting colors are usually mottled brown, gray and cream, but color is the least fixed thing about this animal. During the breeding season mature males show bold black-and-white zebra stripes, and adult males can also be recognized by banded fourth arms. Like all cephalopods, cuttlefish have three hearts and blue, copper-based blood; Why is octopus blood blue? explains how it works.

How big do common cuttlefish get?

This is one of the largest cuttlefish species. In the cool waters of northern Europe, the biggest individuals reach a mantle length of 45–49 cm (18–19 in) and weigh up to about 4 kg (8.8 lb). Cuttlefish from warmer, subtropical seas stay smaller and rarely exceed 30 cm (12 in) and 2 kg (4.4 lb). Because the mantle length measures only the body, the arms add several more centimeters.

Growth is astonishingly fast. A hatchling is barely bigger than a fingernail, yet within about a year and a half it can become thousands of times heavier. Water temperature and food supply strongly affect how quickly cuttlefish grow and how big they get before breeding.

Habitat and range

The common cuttlefish lives in the eastern North Atlantic, from southern Norway, the Shetland Islands and the North Sea, through the English Channel and the Bay of Biscay, south to northwest Africa and the Canary Islands. It is also found throughout the Mediterranean Sea. Farther south along the coast of West Africa, very similar cuttlefish are now treated as a separate species, the giant African cuttlefish (Sepia hierredda).

Surprisingly, there are no cuttlefish of any kind in the Americas. The family’s roughly 120 species live in the seas of Europe, Africa, Asia and Australia.

Common cuttlefish live near the seabed over sand, mud, seagrass and rocky reefs, from the shallows down to about 200 m (660 ft), and they can cope with somewhat brackish water. Many populations migrate with the seasons. In spring and summer they move into shallow coastal waters to breed, and in autumn and winter they retreat to deeper water of about 100–200 m (330–660 ft).

How does the cuttlebone work?

Inside the mantle lies the cuttlebone, a light internal shell made mainly of aragonite, a form of calcium carbonate. It is divided into many thin chambers held apart by tiny pillars, and more than 90 percent of its volume is empty space. By moving liquid into or out of these chambers, the cuttlefish changes the balance of gas and liquid inside and so adjusts its buoyancy, much like a submarine filling or emptying its tanks.

This clever float has a limit. Water pressure crushes a cuttlebone below a certain depth, which ranges from about 200 to 600 m (660 to 1,970 ft) depending on the species. That is one reason cuttlefish stay over continental shelves. When a cuttlefish dies, its body decays quickly, but the white, oval cuttlebone often floats ashore and is a familiar find on European beaches.

Camouflage and color change

The common cuttlefish’s skin holds thousands of tiny pigment sacs called chromatophores, in yellow, orange-red and brown-black. Each sac is ringed by small muscles controlled directly by nerves from the brain, so the cuttlefish can open or close them in a fraction of a second. Below them, reflective cells called iridophores and white leucophores add shimmer and brightness.

Small muscles in the skin can also raise bumps and spikes called papillae, turning smooth skin into a rough surface that resembles rock or seaweed. With these tools the cuttlefish produces three main kinds of camouflage: a uniform color, a fine mottle, or a bold disruptive pattern of light and dark patches that breaks up its outline. Young cuttlefish can already change color inside the egg.

Remarkably, experiments show that cuttlefish are probably colorblind, so how they match their surroundings so well is still being studied. The full story is in How do cuttlefish change color?, and other champions of color change appear in animals that change color.

Diet and hunting

Common cuttlefish are carnivores. They eat mainly crabs and shrimp, along with small bottom-dwelling fish, snails, clams, worms and, when other food is scarce, smaller cuttlefish. By day many lie half-buried in sand, and they do much of their hunting at dusk and at night.

A hunting cuttlefish relies on stealth. It drifts slowly toward its prey, often with its arms raised and its skin matching the seabed, then shoots out its two long tentacles in a split second, grabs the victim with the sucker clubs and pulls it back to the beak. Slower prey such as crabs may simply be pounced on and held with the arms. The cuttlefish then bites through the shell and uses saliva containing toxins and enzymes to subdue and soften its meal.

Early experience shapes their tastes. A 2008 study found that cuttlefish embryos that could see crabs through their transparent egg capsules preferred to hunt crabs after hatching, even though young cuttlefish normally favor shrimp.

Behavior and intelligence

Common cuttlefish are mostly solitary, gathering in large numbers only to breed. When threatened they have several lines of defense. The first is camouflage. If spotted, a cuttlefish may flash a startling display, turning pale and showing a pair of dark eyespots on its back, or it may jet away behind a cloud of ink. A blob of ink mixed with mucus can even form a rough cuttlefish-shaped decoy.

Cuttlefish have large brains for invertebrates and do well in learning tests. In a 2021 study, common cuttlefish learned to pass up a less-liked snack in order to get a favorite food later, waiting from about 50 seconds to over two minutes, a version of the famous marshmallow test. They can also see polarized light, a property of light invisible to humans, and they use it to spot prey and possibly to communicate. Their nearest well-known relative, the common octopus, is similarly famous for problem-solving.

Reproduction and life cycle

Common cuttlefish become mature at about 14–18 months old. In spring and summer they gather in shallow coastal waters to breed. Males display striking zebra patterns and compete, sometimes fiercely, for females, and a successful male often guards his mate afterward. During mating the male uses a specially modified arm to place packets of sperm near the female’s mouth.

The female then lays clusters of eggs, each about 6–9 mm across, attaching them one by one to seaweed, seagrass, shells or ropes. She stains the eggs with ink, so the clusters look like bunches of small black grapes. A female may lay from about 150 to 4,000 eggs, depending on her size, often in several batches.

Development takes about 30–90 days, faster in warmer water. The young hatch as miniature adults about 1 cm (0.4 in) long and begin hunting small crustaceans within days, with no care from their parents. The adults, meanwhile, decline and die soon after spawning, which is why few common cuttlefish live longer than two years.

Predators and threats

Many animals eat cuttlefish, including sharks, dolphins, seals, large fish such as sea breams and other cephalopods, among them larger cuttlefish. Egg clusters are eaten by sea snails, crabs, sea urchins and starfish.

People are the other main predator. The common cuttlefish is one of the most important commercially caught cephalopods in European waters, especially in the English Channel, the Bay of Biscay and the Mediterranean. Because each generation lives only about two years, a poor breeding season can quickly reduce local numbers, and eggs laid in shallow coastal waters are vulnerable to disturbance and damage.

Conservation status

The IUCN Red List classifies the common cuttlefish as Least Concern, in its most recent assessment from 2012. Overall numbers do not appear to be declining, and its fast growth and short life help populations recover quickly. Even so, some fished stocks are considered close to overexploited, and scientists monitor catches in areas such as the English Channel, where cuttlefish are not managed by catch quotas.

Relationship with people

Cuttlefish have long been a favorite food around the Mediterranean, in dishes from Spanish and Portuguese stews to Italian black risotto colored with the animal’s own ink. That ink gave its name to sepia, a dark brown pigment once widely used for writing and drawing, and to the reddish-brown tone of old photographs.

The species name officinalis comes from the Latin for a workshop or storeroom, the same root used for many medicinal plants, because cuttlebone and ink were once sold by apothecaries. Today the common cuttlefish is also a key animal for scientists who study camouflage, vision and the brain. If you are wondering how it relates to fish, see Is a cuttlefish a fish?