Underwater Phenomenon: Deep Sea Gigantism Explained

Delve into the depths of the mysterious deep-sea realm, where colossal creatures defy norms. Discover definitions, theories, examples, and implications of deep-sea gigantism.

Oct 17, 2023By Natasha Elder
deep sea gigantism explained

In the deepest, darkest (and for many people scariest) parts of the ocean, you’ll find an incredible array of creatures that are weird, wonderful, and wildly large.

Why do some deep-sea creatures grow to such massive sizes? What drives this phenomenon known as deep-sea gigantism? How can understanding what’s going on at the bottom of the sea impact life on Earth? In today’s post, you’ll learn the theories behind the phenomenon, and discover which abyssal giants are impacted by this puzzle that scientists have been trying to solve for decades.

What is Deep Sea Gigantism?

giant japanese spider crab deep sea
Image credit: Wikimedia

From scientists to explorers and from children to the elderly, the thought of the deep ocean has long been fascinating to all. The deep sea is extremely large, extremely cold, extremely dark, and extremely pressurized.

Due to the intense conditions at this level, most deep-sea creatures are on the small side. Small, but special. These creatures will often develop biological adaptations like bioluminescence to help them survive at these depths.

But, away from mesmerizing displays of light, there is another way that creatures of the deep adapt. This is where a remarkable pattern known as deep-sea gigantism comes in and defies these norms and challenges our very understanding of biology and evolution.

Deep sea gigantism is a type of biological adaptation that, over time, some sea creatures have developed to help them cope with life that far down. In the very deepest zones of the ocean, certain sea creatures grow to enormous sizes. This could either be fully or partially (for example, tentacles become extremely long, or eyes become incredibly large). But why does this happen?

Theories Around Deep Sea Gigantism

greenland shark sleeper shark deep sea
Image credit: Wikimedia

Did you know that more is known about the surface of the moon than the floors of our ocean and the creatures that inhabit it? It’s not surprising to discover that the exact answer as to why life is so large at such depths is yet to be revealed.

As deep-sea exploration has evolved over the decades, marine biologists and researchers have come up with a few theories that could explain why deep-sea gigantism occurs. If you enjoy watching deep sea documentaries, you’re likely family with the three most popular theories, being Kleiber's rule, Bergman's rule, and the Island Rule.

Kleiber’s rule states that ‘animals that are larger will tend to be more efficient’. In layman's terms, this theory is that bigger animals don’t need as much energy, per unit of their body weight, as smaller animals. They make a little energy go a long way.

deep sea open ocean eery
Image credit: Pexels

Bergman’s rule is summed up as the idea that sea animals grow larger in cold climates. The cold temperature of the deep sea means that cells are larger, and metabolisms are slower. Plus, the abundance of oxygen present in cold water helps them grow even bigger -- albeit over a LONG time, think of this almost like living in slow motion.

The Island rule suggests that the deep sea is similar to the functionality of an island, meaning that resources are extremely limited, and competition for the resources is minimal, and predators are few and far between due to the state of isolation present.

Examples of Deep Sea Gigantism

giant squid eating whale deep sea
Image credit: Flickr

You can observe deep sea gigantism in various underwater creatures ranging from the Greenland shark (which is also one of the longest-living animals known to science) to the Japanese spider crab (which is also one of the creepiest crustaceans of all time).

Some other examples of deep-sea gigantism in action can be seen in:

  • The giant isopod
  • The big red jellyfish
  • The giant oarfish
  • The giant squid
  • The colossal squid
  • The vampire squid (which is not actually a vampiric creature but is a small species of squid.)

Implications of Deep Sea Gigantism

giant squid muséum national d_histoire naturelle
Image credit: Wikimedia

Right now, we have more questions than answers when it comes to our understanding of what deep-sea gigantism is caused by. Understanding what deep sea-gigantism is and how it works could have a much greater impact than you’d think.

Understanding deep-sea gigantism will help to fill in the gaps in many theories around evolution. Learning more about the creatures that this phenomenon is observed in could help researchers understand more about the impact of climate change and deep-sea mining. Figuring out how these creatures survive in such extreme conditions could further biomedical studies. Who knows, the answers to our burning questions could be swimming around the deepest parts of the ocean.

Natasha Elder
By Natasha Elder

Natasha is a mother, a wife, a writer, and a serial cat owner. Though she is currently in mourning, her heart not ready for another feline family member just yet, she has always lived life with four paws beside her. She loves – you guessed it – cats, as well as creatures of the fluffy, scaly, and finned variety. Natasha longs to meet Sir David Attenborough one day and is passionate about responsible pet ownership