Deep Sea Gigantism: Why Do Creatures in the Depth of the Oceans Grow So Big?

Deep sea creatures grow big because their size makes them more efficient in their environment. But why do animals like squid, sea spiders, and worms grow so prominent in the deepest and coldest parts of the ocean?

Deep Sea Gigantism

Compared to the common arrow squid (Nototodarus sloanii) found in New Zealand waters, the giant squid (Mesonychoteuthis hamiltoni) found in subantarctic waters is approximately 14 times longer. Meanwhile, a minivan-sized sea sponge exists in the isolated Pacific waters.

But why do animals grow so large in cold ocean waters? It could be a matter of survival dictated by conditions in the bitterly cold waters that make it possible.

Two general rules dictate deep sea gigantism: Kleiber's and Bergmann's rule.

Kleiber's rule asserts that larger animals are often more productive. Large animals that swim in the ocean's depths depend on food falling from the sky, and since food is frequently short, they have every reason to become larger and more efficient.

Bergman's rule is a common relationship between dropping temperature and growing body size. Larger populations and species are found in colder climates, while smaller populations and species are found in warmer climates. Nevertheless, this is more of a tendency than a rule. This occurs for warm-blooded animals because, relative to volume, a larger animal has less area in contact with the environment. However, this is linked to longer life spans and cell division in marine swimming creatures.

Alicia Bitondo, a senior aquarist working with deep-sea species at the Monterey Bay Aquarium in California, shared the same opinion. According to her, resources are extremely few in the ocean's deepest regions, just as they are in island ecosystems. Only a small portion of the food goes to the sea's depths. The majority comes from shallower areas. A bigger size is a major advantage when food is scarce, per

Bigger animals can travel longer and faster, searching for food or a mate. They store food better and have more effective metabolisms. Big predators may eat more and store that energy when something like a large cadaver drifts down to deeper waters, according to Bitondo.

The extreme cold in the deep water can also cause gigantism in animals since it drastically slows down their metabolism. According to Bitondo, many creatures in this ecosystem, like the Greenland shark (Somniosus microcephalus), develop and mature extremely slowly. This slow-moving shark can reach lengths of 24 feet (7.3 meters) and a maximum weight of 1.5 tons (1.4 metric tons), but its growth occurs gradually over centuries.

Examples of Giant Sea Creatures in the Deep

The largest terrestrial mammal, the African elephant, can grow to a height of 4 meters, but it is dwarfed by the most significant sea mammal, the blue whale, which can reach a length of 30 meters. The blue whale's enormous size illustrates how big animals can develop when not restricted by gravity. Because of the ocean's buoyancy, marine life can expand to the maximum size required to sustain itself. For example, whales must grow to a size that prevents them from losing excessive body heat to the surrounding water.

Due to deep-sea gigantism, several deep-sea species dwarf their terrestrial counterparts. The blue whale is not the only marine animal that has reached enormous sizes.

One example of a deep-sea creature that grows significantly larger than its terrestrial cousins is the gigantic isopod, a massive crustacean related to woodlice, shrimp, crabs, etc. Its astonishing 50cm body length is found on the ocean floor at depths above 500m.

Terrestrial and shallow-water isopods rarely reach lengths of more than 3 - 5 cm. The Japanese spider crab, which lives in the same habitat, has a carapace that measures up to 40 cm in length and claws that stretch up to 3.7 meters. By contrast, a related shallow-water species called the European spider crab can achieve a maximum carapace length of 20cm and a maximum claw span of 50cm.

At depths of approximately 1,000 meters, the gigantic squid, a species that has long captivated humanity and could be the inspiration for stories of monsters like the Kraken, can reach lengths of 13 meters. In contrast, the massive squid that lives in deeper waters can reach a length of 10 meters and a mass of half a tonne. With a diameter of 30 to 40 centimeters, its eyes are thought to be the biggest of any animal on Earth. Most other squid species that inhabit the photic zone, the upper 200 meters of the ocean, only reach a maximum size of 60 cm.

Check out more news and information on the Giant Squid in Science Times.