Large Sea Creatures? Why?

Hundreds of species of sea creatures live in the depths of the ocean, many of which are significantly larger than their shallow water counterparts. Among these creatures is the colossal squid, which can weigh up to three times as much as a regular squid and has eyes the size of basketballs.

But if that doesn't scare you off, here's a subterranean specimen that will get you thinking will leave scars. This "little" animal is a giant isopod worm. If it looks strangely familiar to you it's probably because it's closely related to the humble woodlouse. A well-fed woodlouse is about an inch long and weighs less than an ounce when wet. The giant woodlouse worm, on th`e other hand, can grow to almost half a meter long and weighs almost 2 kilograms.

Everywhere we look in the deepest, darkest depths of the ocean, we see a similar story - familiar-looking animals have mysteriously become dinosaurs.

Like the Japanese spider crab, with a leg span of up to 4 metres, and the giant oarfish that sometimes also known as the king of herrings, which can reach a maximum length of about 11 meters. 11 meters!

It's as if God showed up to work drunk on the fifth day and made a bunch of rounding errors. What the heck is going on here? What causes deep sea species to grow so insanely large?

The truth is, we're not 100% sure. As you probably already know surprisingly little about the ocean floor. In fact, by 2019, more people have walked on the seafloor walked on the surface of the Moon than have visited the deepest part of the Mariana Trench, Challenger Deep.

The sheer remoteness of the deep ocean makes it - and the creatures that live there are incredibly difficult to explore. Take the giant squid as a prime example. As long as long as a London bus and heavier than a full-grown polar bear, you'd think it would be damn hard to miss. And yet, with all our sophisticated technology and remotely operated submersibles, not a single giant squid has ever been observed in its natural habitat. Not a single one!

Since we never have the opportunity to capture one of these animals, research into the causes of deep-sea extinction is giantism in the deep sea is rather difficult - but we do have some surprising theories.

The first is that food scarcity is the main cause. The idea that of food could somehow stimulate the evolution of larger animals may feel like nonsense - the opposite would be true, right? But if you look into the science a bit, this apparent contradiction makes a lot of sense.

Unlike almost all other ecosystems on our planet, in the depths of the oceans there are almost no food production of its own - no light means no photosynthesis, and no photosynthesis means no phytoplankton, which is the main producer at the surface. At consequence, the most important food source in the deep sea is what is known as marine snow.

A delicacy of the deep sea, marine snow is basically a mixture of dead animals, decaying phytoplankton and a whole range of fish shit that slowly drifts into the abyss from the shallow waters above. Sounds delicious!

The marine snow - supplemented by the carcasses of larger animals - is consumed as it falls, that is, the deeper you get, the less there is to spread around. That makes the food on the sea that makes food on the seafloor both scarce and unpredictable - there's not much of it, and you never know where the juiciest morsels will land.

For a bottom-dwelling scavenger like the giant isopod, being bigger means being for a ground-dwelling scavenger like the giant isopod means being able to travel greater distances faster, which increases its foraging radius and increases its chances of being first on the scene when food appears.

Larger animals are also able to shop more food than smaller ones, which helps them survive long periods without food.

Many deep-sea animals have evolved expandable stomachs that allow them to take in the largest amount of food possible on the rare occasions when a solid meal presents itself. The results can be surprising - one giant isopod with the memorable nickname 'Giant isopod No. 1' once went 5 years without eating anything.

without eating anything, presumably in protest at his captivity in the Toba Aquarium in Japan. 5 years without food is undoubtedly a supermodel-level diet, but these long fasts are made possible by another benefit of increasing size - a more efficient metabolism.

According to Kleiber's Law, an animal's metabolic rate scales with a 3/4 power of its mass. To translate that into the language of a normal human: larger animals require less energy per unit mass than smaller animals.

A mouse, for example, must eat up to 20% of its body weight each day to survive, while an elephant only needs to eat 4 or 5% of its body weight. In other words, larger animals use energy more efficiently. And that is an enormous advantage in an environment where food is scarce.

The other main theory as to why creatures from the deep grow so large is related to temperature.

Because cold water is denser and therefore heavier than warm water, it sinks, and the deep-sea environments are therefore extremely cold. Freezing temperatures inhibit the rate of metabolism and reduce the amount of food and oxygen needed to support animal growth.