8 Oct 2020

8 Oct (Thu): Happy International Octopus Day!

October 8th is International Octopus Day! It's no secret why this date has been chosen to celebrate the octopuses - one of the best known marine animal for its intelligence. To celebrate this day, we like to share an article penned by Megan Ng, a budding marine enthusiast who loves to illustrate!

About the author: Megan is currently a third year Life Sciences major with a minor in Aquatic Biology and Forensic Science at the National University of Singapore. Her passion for the ocean started when she was a young girl, as she was always very curious about nature especially marine life. Megan is a strong believer about conservation and tries to find ways to help our planet. She is writing for Celebrating Singapore Shores to spread the word about our marine life and conservation to the public through popular science writing!

So let's dive in and meet the Curvy, Cool Octopuses of Singapore!

An illustration of the octopus by Megan Ng. Photo credits: Beak of octopus to Mark Conlin, Royal Society of Chemistry and chromatophore to Wikipedia Commons.

Cephalopods consist of the flamboyant Squids, cute Cuttlefish, the notorious Nautilus and finally, the acrobatic escapee Octopus! These cephalopods are classified together because they are all blue-blooded, have well-developed chromatophores and have their limbs directly attached to their head. 

Contrary to popular belief, the tentacles and arms of cephalopods are not the same thing!

Arms have suckers going up and down along the entire length of the appendage itself, but tentacles only have suckers at tips. Moreover, tentacles usually have special features such as being able to paralyse prey. Most cephalopods generally have both arms and tentacles!

Among the cephalopods, the octopuses stand out as truly fascinating in their anatomy, behaviour and ecology.

For one, the octopus possesses not 1, 2, or 3 brains. In fact, it actually has 9 brains! Each of its 8 arms have a brain of its own, along with the central brain contained in the mantle of the octopus. These brains are important for moving independently, as well as for sensing, touching and tasting! Within the muscular mantle of the octopus lies its 3 hearts, a central brain and gills. Two of its hearts functions to pump blood to the gills, while the third one circulates blood to the rest of the body.

Octopuses' best defence - outsmarting predators

Octopuses are very smart, intuitive and curious, with the ability to adapt to scenarios very quickly.

A team of researchers from the Hebrew University of Jerusalem studied the brains of an octopus (Octopus vulgaris) and interestingly, they found out that majority of their brains are used for learning and memory. Not only that, their brains are actually organised quite similarly to the vertebrate's brains, although the way both brains work are complete opposite to each other.

An example of similarity is the organisation of layers in the optic lobe of the octopus' brain, which controls its sight, is arranged very similarly to those found in the eyes (retina) of vertebrates. However, the way the optic lobe cells in an octopus detect light and deliver this information to the brain is completely opposite to how the retina cells in vertebrates perceive light! Even though both types of optical organs share similar form and function, both organisms use them very differently to capture and process light information in their brains!

Another unique trait of the octopuses is how quickly they adapt to situational problems and learn quickly from other animals, by mimicking their behaviour and how they look like. They can even recognise people!

The Mimic Octopus has been spotted at Pulau Hantu, Singapore!

But, how does learning fast help them defend themselves? Well, it has been previously observed that most octopus can mimic other marine life and in fact, uses this mimicry to escape predation. They can also use mimicry to court females and challenge competing males as seen in the Mimic Octopus (Thaumoctopus mimicus) and Wunderpus (Wunderpus photogenicus). The Mimic Octopus, for instance, can emulate the behaviour of the poisonous flatfish (Pardachirus marmoratus), as well as change its colours and patterns to mimic the appearance of a banded sea snake (Laticauda colubrina). So far, it has been estimated to be able to mimic more than 10 animals, allowing them to deter predators and make a quick getaway.

Although mimicry is arguably their best trick so far, don't underestimate the octopus just yet! It's definitely a jack of all trades.

An arsenal of defences up their sleeves - literally!

Not only are they super smart and quick on the fly, octopuses also have camouflaging abilities. 

Most cephalopods have special pigments called chromatophores - including the octopuses. Each chromatophore cell is able to change its colour and light intensity, allowing them to change the colour of their skin according to their background - be it a rock or sand, or even to bright colours to warn off predators! Octopuses can also change the texture of their skin by changing the papillae, or protrusions on their skin. This takes their camouflage act to another level, allowing them to really hide in plain sight from predators or even disarm prey. Isn't this cool?

The octopuses' arsenal of talents do not stop here. When they get startled or feel threatened, they can shoot ink from their siphons to hide their escape, much like a ninja and his smoke bombs.

If their predators continue the chase, they may give up as the ink sprayed upon them contains tyrosinase that tastes bitter. Some other octopuses are toxic such as the venomous Blue-ringed Octopus (Hapalochlaena sp.) and the poisonous Mototi Octopus - both of which have been reportedly found in Singapore, though uncommon. In fact, there was a reported death of a young boy from Singapore due to a bite from the highly venomous Blue-ringed Octopus - oh dear!

Mothering till death

On mating, the male octopuses have a special arm known as the 'mating arm' (duh!). Unlike the usual arms meant for movement, this mating arm has a different tissue called ligula. With this ligula, the male octopuses insert this organ through the female's siphon, and into her ovaries to deliver its sperm.

After which, the female octopus will find a cosy spot to lay her eggs and look after them without taking any break -- eventually starving herself and dying right after her babies are born. Here's a toast to this ultimate mother's love! This also means that the female octopus can only reproduce and lay eggs once in her lifetime.

The deep-sea octopus (Graneledone boreopacifica) is known to have one of the longest brooding period of 53 months - nearly 5 times longer than the human's gestation period!! By the time these baby octopuses hatched out, they are fully capable of surviving on their own and hunt by themselves. This long brooding period may partially be explained by the very cold temperature where the species is found, thus slowing the development of eggs.

Singapore's octopuses and where to find them?

Clockwise (L-R): Reef Octopus, Slender Seagrass Octopus, and octopus eggs. Photo credit: Wild Fact Sheets, Wild Singapore.

Yes, we have various octopus species right here in Singapore. They have been seen along Changi Beach, as well as on dive trips to Pulau Hantu and Sisters' Islands. Apart from those mentioned earlier, the common reef octopus and the slender seagrass octopus are frequently encountered on our intertidal shores. On the rare occasions, their eggs can be seen on our shores that are typically attached to a rock -- so be careful not to disturb them during dives or step on them during intertidal walks!

Currently, the taxonomy knowledge of octopuses is not well-established in Singapore, hence many of our octopuses don't yet have their species names. It seems that none of the species in Singapore are listed on the IUCN Red List for Endangered Species. Thus, more information is needed to fully assess the status and distribution of our local octopus species, especially in our highly urbanised and marginal reefs.

Further readings and citations

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