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Episode 342: Giant Pacific Octopus Astounds

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The magnificent Giant Pacific Octopus (image from OctoNation)

The Giant Pacific Octopus, as the name would suggest, lives throughout the Pacific Ocean anywhere from the sunlit surface to depths of 6600 metres. They like rocky coastal areas, where they use tide pools and rock crevices as lairs and dens.

They are the largest known species of octopus, ranging from 70 to 110 pounds. Like other octopus, they have three hearts, one from circulating blood throughout the body and two for passing blood over their gills for oxygenation. In the mantle, which is the bag shaped body of the octopus, are the organs; the liver, kidneys, a stomach, gills, reproductive anatomy and even a separate brain. Their eyes are structurally similar to humans, despite how vastly far away they are on the evolutionary tree.

Their mouth sits underneath the mantle, where the eight tentacles meet. Here they have a beak made of keratin, which is the only hard part of the octopus body. This feature makes octopus so incredibly flexible and phenomenal escape artists, as they can fit through any space provided their beak can. They have pigment cells called chromatophores all over their body, which allows them to change colour to blend into any background. Famously, they can also release a cloud of black ink to confuse any predators that might be after them. Generally though, octopus prefer no confrontation, and spend most of their day hiding in small crevices and at dawn and dusk emerge to hunt mainly for shellfish, although they predate on many species including crabs, clams, shrimp, fish and have even been seen catching and killing sharks and even the occasional bird!

Big brains of the ocean: cephalopod intelligence

Cephalopods, particularly octopuses, are consistently ranked as the most intelligent invertebrates. They show incredible neural and behavioural plasticity and impressive learning and memory, leading to some pretty entertaining behaviours. Researchers have caught octopi escaping from sharks by shoving their tentacles into their gills to fight them off. They are known to use coconut shells as armour, barricade their dens with stones and unscrew lids with their tentacles to get at food within. Octopuses can use their siphon to squirt water at high velocity at predators, but this skill has become particularly problematic in captivity, where irritated octopus have been known to fire jets of water at buzzing aquarium lights! And this isn’t the only mischief they get up to in captivity. Octopus have been known to escape from their tanks at night when all the staff have left and nip over to neighbouring enclosures to steal some clams as a midnight snack, and make it back in time before the aquarium opens and they are caught in the act. Studies in aquariums have also revealed an incredible fact, that octopus can recognise individual humans. In one aquarium in New Zealand, one unfortunate aquarist was consistently soaked by one disgruntled octopus who had taken a dislike to her, with none of her colleagues being on the receiving end of a jet of water to the face every time they walked past the tank.

Their incredible intelligence makes octopus very unusual. Most invertebrates are simple animals with basic nervous systems, but most species of octopus have on average around half a billion neurons. Most of these neurons are in the octopus arms, which can touch, taste and move without any oversight from the brain. Even arms that have been surgically removed from the octopus can move around and grasp items. They are also solitary animals, and rarely do solitary animals develop such intelligence. Usually species evolve intelligence as a part of being social. What gives the octopus such unusual intelligence for an invertebrate?

The incredible anatomy of the octopus. Note that their beak is the only hard part of their body, the secret behind their incredible ability to squeeze into any gap!

As soft bodied molluscs, the octopus and other cephalopods are soft bodied, making their fossil record non existent. To study their evolution, scientists have turned to their genome to decode their past. 530 million years ago, the shell covered mollusc ancestors of modern day octopus modified these protective shells into buoyancy aids, filling them with gas. This allowed them to move off the sea floor and swim. Around 275 million years ago, evolutionary pressure acted on these early cephalopods, driving them to become faster swimming and more agile to avoid predators. Thus the octopus was born, as they shed their shells to move faster, and migrated to deeper waters to avoid the plethora of predators near the surface. However, this lack of shell made these early octopuses particularly vulnerable to predators, and some scientists hypothesise that this forced the cephalopods to develop more behavioural plasticity to learn how to avoid being someone’s dinner, like barricading their dens with coconut shells and learning to attack sharks in the gills to drive them off.

Genetic studies have revealed some of the secrets of octopus intelligence. A investigation into octopus genomes found transposons, or so called ‘jumping genes’ that can cut and paste into other parts of the genome, driving evolution. These transposons are very important for learning and memory, and some scientists think this mechanism might be the key to helping octopuses and other cephalopods survive changing oceans. These studies also found a family of genes, called protocadherins, which are similar to the ones found in humans, and are involved in the development of complex neural pathways. Recently it was discovered that octopus even have genes that allow them to taste with their suckers!

Flexible enough for changing oceans?

Currently, the IUCN has not evaluated the Giant Pacific Octopus as part of its red list assessments, largely down to difficulties in studying octopus and a focus on other, more vulnerable species. However, this does not mean the Giant Pacific Octopus is necessarily home and dry (or should that be wet?) when it comes to surviving in the changing oceans.

Many of the prey items that make up octopus diets are filter feeders, like mussels, and in these species it is very easy for toxins and pollutants, such as those from agricultural run-off or urban waste, in the water to build up, as they are filtering quite large volumes of polluted water through their bodies. When the octopus eats these animals, these toxins build up to dangerous levels in their tissues, which is not only potentially fatal for the octopus, but also serious for humans, who in many coastal areas, often very poor ones, eat the octopus as a source of protein. In a study of local seafood markets in Tanzania, it was found that in every octopus the levels of lead were too high for human consumption. And this will not just affect humans, but also the diverse array of species that also eat the octopus, including large fish, dolphins, whales and sharks, who will build up the toxins at even more concentrated amounts, being at the top of the food chain.

Octopus biology puts them at an increased risk from changing oceans. Octopus blood has a pigment called hemocyanin rather than haemoglobin, as in mammals, which is copper based. This blood is far less efficient at carrying oxygen, which is why octopus prefer cooler, oxygen rich waters. Changes in PH or temperature will affect their oxygen carrying capacity, which could be fatal and will certainly limit available habitat. Oceanic temperature changes can also affect egg development; in warmer conditions, the eggs develop and hatch faster, and the larvae may hatch at the wrong time of year when food is limited. Lab based studies found that increased temperatures increased the speed of all elements of reproduction and even shortened the lifespan of the test octopi by up to 20%. Currently, a lot of the research around how warming temperatures may affect octopus biology and their role in the ecosystem, there is certainly evidence that raised ocean temperatures and changing water PH levels could equal higher embryo and paralarvae mortality.

Giant Pacific Octopus larvae. These tiny animals are potentially very vulnerable to oceanic warming and acidification (image from NPR)

Although octopus may be able to show some resilience to changing oceans, their food might be at risk as the oceans become more acidic. Increasing surface ocean temperatures mean that calcium carbonate ions in the seawater will begin to precipitate out, which not only lowers the PH of the water but also reduces the amount of carbonate ions that shell building animals, like clams, scallops and mussels can take up. Many of these species make up a large part of the octopus diet, so even with physiological and behavioural resilience to climate change, their prey base could be at significant risk.

Sadly, octopus have not escaped the scourge of marine ecosystems: plastic waste. They have been seen using plastic waste to shelter themselves from predators and barricading their dens with plastic barrels and bottles. To look at this with a more positive angle, this does show their incredible ability to adapt!

An octopus looking for a home among the plastic debris littering the seafloor (image from Forbes India)

Currently, the Giant Pacific Octopus, and many cephalopod species in general, are not evaluated by the IUCN red list. This is largely down to the fact that it is very difficult to evaluate octopus populations in the wild, but there is more research desperately needed to determine exactly what the future of this incredible species will be. Although their physiology puts them uniquely at risk from ocean warming and acidification, their incredible brains and nervous systems could give them a real fighting chance. To learn more about those on the cutting edge of octopus research, check out Monterey Bay Aquarium and their work with this incredible species at Giant Pacific octopus | Animals | Monterey Bay Aquarium.

Awesome Videos!


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September 06, 2023
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