by Matthew Norton
Communication can be a tricky business in the sea. For many animals, it is impossible to complete their life cycle without sending and receiving messages with their own kind. But they often do so at the risk of giving away their position to their enemies. Sounds can be eavsedropped, odours and chemical trails can be followed with hungry noses and visual cues can be picked up by everyone in the local vicinity. It is a necessary risk, but it can also be managed by developing communication systems that are selective in who they talk to.
Cuttlefish are a great example of this with their ability to change their appearance at a moment’s notice. They achieve this feat with chromatophores, specialised skins cells that can be stretched and relaxed to create changes in colour and contrast. Changing a single chromatophore sounds as simple as flicking a switch, but with the incredible cuttlefish brain they can coordinate millions of these switches at once. This system makes cuttlefish highly accomplished masters of disguise who can mimic and blend in with virtually any habitat. Not bad for a group of animals who are all colourblind and only have the contrasts between light and dark to work with.
It is also worth mentioning that the animals in the sea see the world very differently.
When cuttlefish want to make themselves seen, they can still use those same colour changing abilities, in combination with other visual cues such as moving their tentacles and adopting certain postures. The resulting colourful displays are often used to ‘talk’ to other cuttlefish (of the same species) during reproduction to indicate their gender, readiness to mate and to threaten romantic rivals. If they sense danger approaching, they can switch all their chromatophores to stealth mode and then pick up where they left off once they get the all clear.
But the need to reproduce can make fools out of many animals, and cuttlefish are no exception. In the Australian giant cuttlefish, the possible fools are the large brutish males who honestly display their suitably as a mate and the superiority of their genes to seduce multiple females. The smaller males in the vicinity would not stand a chance against such fierce competition and so resort to sneakier tactics. Instead, they use their own colour shifting abilities to mimic the appearance of a female to deceive their way past another male and mate with his females when he’s not looking.
During the breeding season, sneaky smaller males mimic the patterns of a female to gain the confidence of a large male to gain access to his females. Once the large male is distracted, probably fighting off another rival male, the sneaker male reveals his true identity. With a bit of luck, he can get a few matings in before he has to scarper.
For all their impressive abilities, cuttlefish are sometimes overlooked when compared to their squid and octopus cousins. The main distinguishing feature that cuttlefish possess is the cuttlebone, a shell they keep inside their body for controlling their buoyancy in the water. It may not sound like a particularly interesting namesake, but it is what makes cuttlefish unique among the cephalopods. And let us not forget that the evolution of the human race really got going with the simple breakthrough of opposable thumbs.
Liquid can be filled in, or drained out of these chambers to make it light, or heavy as needed by the cuttlefish.
From a human perspective
Cuttlefish have proven to be a very useful natural resource for us and it appears that little is wasted from those we catch from the sea. For starters, we eat them in seafood dishes such as calamari and linguine where cuttlefish can be a cheap and tasty alternative to squid. This has proven to be popular in seafood cuisines in East Asia and the Mediterranean regions, but cuttlefish are also caught here in UK waters. But, as with any other seafood, it is important to buy and consume cuttlefish that have been caught sustainably with gear that causes minimal damage to the environment.
Sometimes the ink sack is removed and discarded, but in other dishes (like the one depicted above) he ink is served with the meat as a sauce.
Throughout history we have also harvested cuttlefish for their ink to use in writing, drawing and painting. This practice is believed to date back to ancient Greece and Rome, but was probably at its most popular and refined during the 18th and 19th centuries. Only for cuttlefish ink to then become obsolete as alternatives were manufactured on an industrial scale. As for the ink itself, it typically produces a brownish colour with a hint of violet (though variations do exist) after it is extracted from the cuttlefish’s ink sac. The extraction process, depending on the exact method used, could involve drying the ink sack before subjecting the ink to a series of chemical treatments to make it more or less permanent. As demonstrated by some of the images below.
Sepia toning was also once used to treat photographs (top right) and leave them with a brownish tint (which is where the name comes from even though sepia ink wasn’t actually used. Today, sepia toning is done digitally rather than with chemical toners (bottom right).
The previously mentioned cuttlebone has also proven to be a useful part of the cuttlefish anatomy with uses that include an ingredient in polishing powder and toothpaste, a strong mould in jewellery making and a possible use in producing building lime. Cuttlebone also has nutritional benefits due to it being rich in calcium and other minerals, and has been used as a food supplement for pet birds for over a hundred years.
Depending on the species of bird, the cuttlebone is simply hung in the cage for the bird to scrape and munch on, or it is ground into their food. The supposed health benefits include stronger bones, more effective blood clotting, a better immune system and so on. However beneficial a cuttlebone rich diet may be, there have clearly been financial incentives for supplying these supplements. During the research for this article I discovered a patent application (that was accepted) from 1885 for a new bird cage accessory for holding a piece of raw cuttlebone.
Mr. Boerner had this patent enforced for the rest of his life and given that cuttlebone supplements are still recommended for pet birds today, it was probably a wise business decision.
Talking about the impact that marine animals have had on human culture and history can be a double edged sword. On the one hand, it is important to highlight just how connected we have always been with the oceans and appreciate what they have given us over the years. But this connection is often about us exploiting the natural world, sometimes stripping it bare when it suits us. But in the case of the cuttlefish, it is somewhat reassuring that we have found ways to use the less palatable parts of the animals rather than just throwing them away. If we are to use the oceans and its inhabitants for our benefit, we can at least do so as sustainably and efficiently as possible.
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Our world under the waves 
You have a great blog and it’s great to see a fellow underwater enthusiast 🙂
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