The Secret Life of the Common Cuttlefish

Having been struck by what seems like an unusually high number of cuttlebones on our local beach this summer, we realised how little we knew about this fascinating creature.

So we decided to do some research!

The common cuttlefish – some interesting facts

Let’s start with its scientific name: sepia officinalis. Also known as the European Cuttlefish and the European Common Cuttlefish. It is part of a group of molluscs known as cephalopods, along with the octopus and the squid.

There are over 100 species of cuttlefish, but the common cuttlefish is one of the largest and best-known of the species.

Cuttlefish bones

The white chalky, oval-shaped cuttlebone that we see washed up on beaches is actually an internal shell. These are often used as a calcium-rich dietary supplement for domestic birds.

Where are they found?

They are found around all the coasts of the UK, but are more common in southern areas of England and Ireland. They are also found throughout the Mediterranean and along the northern coast of Africa. As a migratory species they tend to spend the spring and summer inshore for spawning, then move to depths of 100 to 200m during the autumn and winter, living on sand and mud seabeds.

Generally, the cuttlefish found darting around the colder waters of the UK grow to a maximum size of around 25-30cm, but those living in the warmer waters of the Mediterranean and Africa can grow to up to half a metre in length.

What do they look like?

These elusive creatures have an almost alien-like appearance. They are best described as a chunky squid-like creature, with a broad, well-developed head, large eyes (with unusual W-shaped pupils) located on either side and a mouth with beak-like jaws.

It has a flattened body, with two fins running along either side, and eight arms with multiple rows of suckers on each. It also has two long tentacles, like its cousin the squid. These are used to quickly grasp its prey, which it then manipulates into place using its arms. But these tentacles are kept tucked away in pouches by the side of the head when they are not being used.

Their colour varies, but they are usually blackish-brown, mottled or striped. However, they have the chameleon-like ability to change both the colour and the texture of their skin to blend in with their surroundings to escape the attention of predators or to attract mates.

They can easily mimic different types of seabed and will sometimes even sink right into a sandy seabed, with only their eyes showing, to hide from a predator.

The fin that goes around their body looks like a skirt. This is used for swimming and when they need to move quickly, they can expel water and move by jet propulsion.

When threatened they may release an ink, known as sepia. This is released in a cloud that confuses predators, allowing the cuttlefish to get away. In days gone by this ink was used for writing and drawing. Today, it is believed to have many health benefits, including anti-inflammatory and anti-cancer properties. It is also used in the food industry, both for its flavour and as a food colourant.

What do they eat?

The common cuttlefish is a fierce predator. It feeds on the seabed, on a variety of different food sources, such as small crustaceans (crabs and prawns), small fish and molluscs (clams and snails). Sometimes, if prey is scarce, they may even eat other, smaller cuttlefish. They have a beak in the middle of their arms that they use to break the shells of their food.

How do they reproduce?

Cuttlefish have short lifespans of 1-2 years. They reach sexual maturity at 14-18 months of age and lay eggs in spring and summer. During the breeding season the male cuttlefish will display a black and white zebra pattern on its mantle to attract females, while the females display a uniform grey colour to indicate that they are ready to mate.

During mating the male transfers a sperm mass to the female’s mantle, where it is released to fertilise the eggs. These remain in the oviduct of the female for anywhere between 30 and 90 days before they are laid. The female attaches her eggs in groups onto objects, such as rocks, shells or seaweed, on the seafloor to stop them drifting away. She stays with them until they are hatched, but both the male and female die shortly afterwards.

Who are its predators?

Sadly for the cuttlefish, it has many predators. Sharks, dolphins, seals, fish and other cephalopods, which includes other cuttlefish. However, they do have some defensive mechanisms up their sleeve to help protect them – including a siphon which can be used to shoot water out to rapidly propel them away from danger, ink which can help to distract and disorientate a predator, and their camouflage abilities which help to disguise them.