Since man started roaming the oceans there have been numerous accounts of giants in the deep. Some are pure fiction while some are just mind-blowing given the size of the described leviathans. In this series, we take a look at the deep sea giants that roam our planet's waters. From majestic mammals such as sperm whales, to giant isopods, colossal squid and deep-sea spiders.
But before we go into the enormous sizes these animals possess let's take a step back and look at why these deep-sea animals are humongous.
Deep sea gigantism
In the deepest and coldest parts of the ocean, sea creatures — mainly invertebrates, or animals without backbones — can reach gargantuan proportions. Squids, sea spiders, worms and a variety of other types of animals grow to sizes that dwarf-related species around the world. The phenomenon is called gigantism.
In recent years, scientists have discovered a new trend. Organisms living near the bottom of the sea not only tend to be weirder, but also significantly larger. In fact, many invertebrate animals inhabiting deeper levels of the ocean attain huge sizes much greater than their shallow-water relatives. There are many examples that exhibit this trend.
The colossal squid (Mesonychoteuthis hamiltoni) in subantarctic waters is about 14 times longer than the arrow Squid (Nototodarus sloanii) common to New Zealand, according to Te Ara the Encyclopedia of New Zealand. These 14-meter and 750 kilogram monsters are found as deep as 2133 meters (7000 feet) below sea level, an astonishing depth for any squid.
As if that's not enough, deep in the remote Pacific waters there's a sea sponge the size of a minivan. But what is it about deep and frigid ocean waters that causes creatures to grow so big? It may be that survival demands it, and factors in the extremely cold waters enable it to happen.
In the deepest parts of the ocean, resources are severely limited, much as they are in island ecosystems, according to a study published in 2006 in the Journal of Biogeography. Much of the food originates in shallower waters; only a fraction trickles down to the sea depths. When food is scarce, being bigger provides a huge advantage.
Larger animals can move faster and farther to find food or to locate a mate. They have more efficient metabolisms and are better at storing food. So when something like a big carcass drifts down to deeper waters, big predators can consume more and store that energy for longer. This fits into Kleiber's law which states the larger an animal gets, the more efficient its metabolism becomes. Giant isopods exhibit this very clearly. They gorge on food when available, to the point of compromising their ability to locomote; this allows them to go for years without eating. In captivity, they have been observed to go 5 years without food.
Another reason that accounts for deep water gigantism is Bergmann’s rule, which states that animals living in colder climates are generally larger than those living in warmer climates. In this case, the cold water and lower oxygen content render a decreased growth rate, and thus a longer growth period for the animal, contributing towards larger body sizes. Though largely a general correlational concept, Bergmann's rule appears to fit deep-sea gigantism since deeper waters are conspicuously more frigid. A great example of this is the greenland shark which matures very slowly. This slow-moving shark can grow to be 24 feet (7.3 meters) long and can weigh up to 1.5 tons (1.4 metric tons), but that growth is spread out over a lifespan that extends for centuries. Greenland sharks grow approximately 0.4 inches (1 centimeter) per year and don't reach sexual maturity until they're around 150 years old.
For the deep sea giants, their enormous size helps them avoid predation or at least reduce the risk of it. Being huge means other animals will more likely feel threatened.
The deep ocean is all too often depicted as a ghastly, nightmarish, and menacing wasteland resided by the “evilest” and most hideous and callous creatures. While deep sea animals’ overarching sizes and seemingly “violent” appearances have never failed to give them a fairly bad reputation, deepwater animals have evolved these adaptations with reasons.
Join us as we explore "Divers of the Deep".
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