The common octopus is an extraordinary creature. It’s a molluscs – a relative of the slugs and snails you find in your garden, and along with the cuttlefish, squid and nautilus, belongs to a group of marine molluscs known as cephalopods. Literally translated the name means “head-footed”, and the bizarre-looking cephalopods certainly look as if their tentacle-like arms sprout straight from their large heads.
The common octopus has a worldwide distribution in tropical, sub-tropical and temperate seas. Here in Ireland it is approaching the north-eastern limits of it’s Atlantic range, and occures off the south and south-west coasts, and up the east coast as far north as Dublin Bay. The species may be extending its range northward as water temperatures rise through the effects of climate change.
Common octopuses live in coastal waters and the upper part of the continental shelf up to a maximum depth of about 150 metres (492 foot). Small specimens are sometimes found in deep rock-pools on the extreme low-shore, although they can be very difficult to spot given their exceptional ability to blend in with their surroundings.
This is a medium to large octopus that can reach lengths of over 1 metre (3.3 foot), but which is generally nearer the 60cm (c. 2 foot) mark when fully grown. It has a well developed head, large, complex eyes that give it excellent colour vision, beak-like jaws and eight muscular arms each lined with a double row of suckers. Although it can change both the texture and colour of its skin at will, it tends to be a mottled yellowish or greenish brown, and the skin of the body is generally covered in raised bumps or warts.
Octopuses are predatory, and actively hunt crustaceans and bivalve molluscs. They are mainly nocturnal, although they do occasionally emerge from their lairs for a daylight hunting sortie. To get about over short distances octopuses crawl along using their arms and suckers, but when they need to cover greater distances, or when speed is of the essence they use jet-propulsion. By contracting the muscular mantle an octopus can expel a jet of water in any direction it chooses through its funnel-like siphon, conveniently thrusting its body in the opposite direction.
The octopuses peerless ability to change colour isn’t all about concealing itself – colour can also reflect the animals mood, and octopuses have been observed to turn white with fear and red with anger. Colour change also plays an important role in the ritualised courtship display that is a precursor to mating.
After mating the female octopus lays anything from 120,000 to 400,000 eggs, each smaller than a grain of rice. She guards the eggs, cleaning them with her suckers and fanning them with oxygenated water until they hatch. This brooding period can last from 25-60 days, depending on the temperature of the water, and the female does not leave the eggs to feed during this time. Many females die soon afterwards.
Once hatched the octopus larvae drift in the plankton for about 40 days before settling to the sea bed at a size of around 12mm (0.5 inch). During this time many become food for other animals, and in all only one or two of the original brood will survive to adulthood.
Although we don’t tend to eat much octopus in Ireland in many parts of the world they are considered a delicacy. Commercial octopus fisheries land between 20,000 and 100,000 tonnes of common octopus each year.
Fionn Mallon says
On the N. Eastern limits of their Atlantic range, the common octopus is abundant along the Irish sea coast as far as Howth head and presumably further north still. Perhaps the S SW coast was the extent of distribution in the past, however due to global change and the associated rising sea temperatures, the previous limiting effects of temperature on species distribution are becoming less and less. Therefore data pertaining to species distribution which is not very recent should be taken with a pinch of salt!!
Not a bad article though.
Thanks Fionn, the profile was originally researched and published some time ago… I will revisit the distribution information and update it as soon as I get chance.
I can remember catching the odd one here in Donegal bay during the summer. This would have been around 15 years ago. Thanks for the article.
Just saw a small octopus, stranded on the shoreline rocks at Seapoint/Monkstown yesterday, as the tide went out – appeared mostly white, about 40cm
Julia Nunn says
Sorry to say that the so called ‘common octopus’ Octopus vulgaris is very very rare around Ireland. The common species in Irish waters is Eledone cirrhosa, the curled octopus. You can differentiate them by the number of rows of suckers on their arms. Octopus vulgaris has TWO rows of suckers, Eledone has ONE. And you have to be careful as Eledone will curl its arms so that the single row is folded and may superficially look like two rows.
Octopus vulgaris is so-called as common because it is common in the Mediterranean.
Julia Nunn, National Museums Northern Ireland
Calvin Jones says
Thanks for the comment and for pointing out the presence of another octopus species around Ireland.
I’m aware that the lesser octopus (aka the horned octopus), Elodone cirrhosa, occurs around all Irish coasts… we used to get them frequently around the Isle of Man when I was studying at the marine research station there.
In hindsight it would help, for the sake of clarity, to mention that in the article — which I’ll amend to that effect when I get chance.
The common octopus’s range does extend to Ireland’s south and east coasts, as outlined in the article and on the MarLIN site here.
When I get chance I will add a profile for Elodone cirrhosa to the site as part of an ongoing series of species profiles, but I can’t say exactly when I’ll get to it. I’m always keen to encourage guest contributors though — so if you’d like to submit a profile for Elodone then please get in touch via the contact form and we can sort out the details.
Meanwhile, for those interested here’s a link to the MarLin page for Elodone cirrhosa, showing its distribution around Ireland.
Declan Quigley says
I would agree with Julia.
I am currently working on a review of Octopus vulgaris in Irish waters and as far as I am aware there are only three authenticated records from Irish waters: 2 from “Dublin Bay” during the late 1800s and one from Dingle Bay during 2005.
Calvin Jones says
Looks like I’ll need to update the article to reflect that.
It’s odd… because the distribution data for common octopus I found both when researching and writing the original profile for Ireland’s Own (quite a few years ago now, it has to be said) and looking around online just now, suggests that its range extends at least to the south coast of England and Ireland (as shown in the MarLIN distribution map — where they explain “MarLIN distribution maps are based on published species records from 1950 to the present day and include fauna and flora together with recent records and verified sightings from Britain and Ireland.” The MarLIN site is run and curated by the Marine Biological Association of the UK — so you’d think it a reputable source.
There’s also this Aquatic Species Distribution Map for Octopus Vulgaris from the “Food and Agriculture Organisation of the United Nations”, which shows the species as “certain” all around the British Isles.
All things considered though, there’s a lot to be said for local knowledge. I’ll do a bit more digging, and will update the article accordingly. I’ll also fast track a profile for Eledone cirrhosa to counterbalance it.
Thanks again to you and Julia for the input.
Tony burke says
Just seen my first octopus diving newfee10m in Kilkee co Clare last evening
Got some pics too but broke my connection for iPad so can’t post them 🙁
Clark Groves says
Found a small hand sized octopus in rock pool beside Ballyholme yacht club today Sunday 6th October. It was still alive add shooting small squirts of water into the air .
Clark Groves. Bangor N Ireland
Jimmy What says
I found a stranded small (head was about 14 cm long) octopus two months ago at the start of Shankill beach, beside Bray pier. I wasn’t able to manoeuvre it back into the sea, it looked a bit angry. I thought it might be able to do that itself and we moved on. When I got back 15 minutes later it was gone, so either the seagulls got it, or maybe someone put it in a bucket and brought it to the sealife centre. That’s what I hope happened anyway.
Breandán Mac Searraigh says
I found an octopus today in Carlingford Lough.
Con Horn says
Found an octopus on the beach in Ringabella yesterday. It was white with green patches around its head and red veins on it‘s arms. Managed to get it back into water and it was gone.