Explore the deep of inner space
It’s Halloween in the ocean too
Down in the depths of the deep blue sea it’s spooky season every day. Down there are vast expanses of unexplored ocean and eerie inhabitants lurking in the dark. Though the ocean covers over 70% of the surface of our planet, humans have explored and charted a mere 20% of the depths, and physically witnessed just 5%. Further fuelling the terror that is thalassophobia1, we remain quite literally in the dark about what may be dwelling in the alien realm of the deep sea, worlds away from familiarity at the surface.
Reaching almost 11,000 metres below sea level, the deepest part of the ocean is known as the Challenger Deep. Found at the southern end of the Mariana Trench, it was first located by HMS Challenger on their 1872 expedition. Of course, they weren’t able to dive to these depths at the time, but as technology has evolved some 27 brave souls have taken the trip down so far, witnessing the incredible species at the deepest part of planet Earth. Some of those skulking along in the gloom are the stuff of nightmares, including moray eel, goblin sharks, the frilled shark, angler fish, lamprey, northern stargazers, big-eye jellyheads, the Sloane’s viperfish and the vampire squid. The vampire squid isn’t scary-looking at all (it’s rather cute actually), but in such a cold, dark and pressured environment something named after a blood-sucking villainous creature is probably not your friend.
And deeper means not only scarier, but also bigger. Known as deep-sea gigantism or abyssal gigantism, this phenomenon is the tendency for invertebrates and other residents of the deep to grow astonishingly large. Much, much larger than their shallow-water relatives, in fact. Most likely driven by the frigid temperatures, reduced predation pressure, food scarcity and an abundance of dissolved oxygen in this environment, exactly why deep-sea creatures are able to grow to such sizes is still up for debate, but scientists usually put it down to two possible reasons.
Firstly, Bergmann’s rule, which suggests that the cold temperatures produce larger animals, while in warmer climates animals are smaller. This is primarily based on the knowledge that warm-blooded animals with larger bodies find it easier to retain heat in colder regions due to a more favourable volume to surface area ratio. Yet, in the ocean, this ratio is linked to cell division and extended life spans, rather than thermoregulation.
Or, if Kleiber’s law is to be believed, larger animals are more metabolically efficient and can conserve more energy between meals. For example, a cat may be one hundred times heavier than a mouse but it will consume only around 32 times the energy the mouse uses. This is particularly useful for deep-sea dwellers as food is likely scarce, and so they are driven to enhance their efficiency and eat less frequently. Thus, they evolve to become larger.
Whatever the answer, our inability to study and observe these animals only adds to the mystery of their enormity.
Some giants of the ocean who have grown to tremendous sizes, especially in comparison to similar creatures closer to the surface within the water column, include:
Colossal squid: This rarely spotted behemoth is almost a thing of legend. Stretching 14 metres long, it is the largest invertebrate to exist and has the biggest eyes of any creature on earth2. Found in the waters of Antarctica, we know very little about the colossal squid but we do know that they’re not something we’d be too keen to brush shoulders with in the dark.
Greenland shark: One of the largest cartilaginous fishes, this pensioner of the sea is the perfect example of what cold, deep environments can produce. They can grow up to seven metres in length, dive as deep as 2,200 metres, and weigh up to 1.5 tonnes. Living at least 250 years thanks to their very slow metabolism and adaptation to their bleak environment, they’re rarely encountered by humans — maybe that’s the real reason they can live so long.
Giant tube worms: Though their name doesn’t fill one with a great deal of comfort these monster worms are the world’s heaviest and grow to 2 metres in length within an extreme environment. The towering colonies of a giant tube worm are able to grow where hot, mineral-laden water bursts out of the seabed and it's the tiny bacteria in this water that they consume for energy, rather than sunlight. Quite convenient when you’re at the bottom of the ocean.
Giant isopod: If creepy critters give you the shivers, then giant isopods are the enemy. An abundant species in the deep waters of the Atlantic, Pacific and Indian Oceans they are known for their resemblance to the tiny, by comparison, common woodlouse, to which they are related. Their 16 inch body is a great example of deep-sea gigantism as they are much larger than their other isopod relatives who usually grow to around 5cm.
Giant Pacific octopus: The reddish-pink mottled skin of the giant Pacific octopus is their secret weapon, allowing them to change colour and disappear entirely in arguably the world’s most effective camouflage3. A solitary animal, they can grow up to nine metres wide but are capable of living in shallow water or depths of 1500 metres. It’s also hard to be too frightened of an octopus as they’re just so beautiful!
The giants of the deep are the animals we know the least about and with 80% of unexplored ocean surrounding us who knows what else could be lurking out there in the dark of the deep. Free to grow to gargantuan proportions, the unknown is quite terrifying, but the reality is worse. Research into life on the seabed and the impact of deep-sea mining has introduced us to some remarkable new species, giving credence to the concept of the deep ocean as ‘inner space’. But if deep-sea mining is allowed to go ahead these species will be gone before we even had the chance to get to know them and their unique ways of living. Thankfully, the world is waking up to the impact we’re having on fragile ecosystems and very recently the UK joined the cause and backed the suspension of deep-sea mining. The moratorium is gaining momentum to stop the irreversible destruction of ancient deep-sea habitats.
Good news for the monsters of the deep.
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Amie 🐋
An intense fear of deep water. Yep.
The giant squid can grow longer tentacles than the colossal squid but it doesn’t have as large a body mass.
Made all the more impressive as scientists believe they might be colour blind.
I’m rooting Octopi 🐙 everywhere!!!
They’re my favorite sea animal, my favorite land animal being Rats! 🐀