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Deep-sea gigantism is the tendency for deep-sea creatures to be much larger than their shallow-water counterparts. Occurring mainly in invertebrates (animals without spines), the most notable examples are giant and colossal squids. However, this can also occur in crustaceans like the giant isopod. Fish—for example, the Greenland shark—are also products of this phenomenon. Some of the most colossal creatures in our oceans dwell in deep trenches and extreme conditions, causing exciting and frightening adaptations unlike anything we see on the surface. But why does this happen?
A thousand meters below the surface, no sunlight can penetrate the water. At this depth, no photosynthesis can occur, meaning that there are no plants available for animals to eat. Because of this, most of these animals have to rely on “marine snow.” It sounds pretty, but marine snow is actually detritus, or fine particles of dead organisms and fecal matter that rain down from shallow waters to the deeper parts of the ocean. Some animals sustain themselves solely on marine snow, but there isn’t enough to support all of the animals in the ecosystem. Instead, most animals don't eat marine snow, but instead prey on the creatures that do. This means that the smaller the animal, the bigger the target on their back. Size is a biological advantage, and the concentration of predators causes an extremely intense and competitive environment in the deep ocean.
However, size has another advantage. Essentially, the larger an organism is, the slower its metabolism works. Kleiber’s law states that the metabolic rate of an organism does not depend on animal size, but on animal mass. Instead of a 1:1 ratio, an animal's metabolic rate scales to the ¾ power of body mass. An exceptionally large organism could burn as low as 45 calories per day. With the pressure of predation and food scarcity, a large creature would need to hunt and eat less. For example, a giant squid's metabolism is so slow that it needs, on average, one ounce of food every day. The colossal squid is even heavier. A single adult toothfish would feed a colossal squid for about 200 days. Such a large size is an extreme advantage for this environment where food is so scarce.
The cold is another challenge these creatures have had to adapt to. Due to the lack of sunlight, the temperatures in the deep ocean are extremely low. The deepest zone in the ocean, the hadal zone, has average temperatures of just above freezing, around thirty two degrees fahrenheit. This unfriendly environmental temperature forces deep sea creatures to adapt to maintain their body heat in the extreme cold. This is another reason gigantism is advantageous. The more surface area an animal has, the more heat it loses. But a creature with a high body mass has a higher body mass to surface area ratio. In simple terms, the larger a creature, the less heat it will lose. This is an effective way to maintain body heat in such a challenging environment.
Most have heard of the Mariana Trench, the deepest spot in the ocean. At its deepest point, the Mariana trench is about 36,201 feet below sea level, or nearly 7 miles. The pressure can reach up to 1100 times the pressure of the surface, and there is no light. But 90% of marine snow, the backbone of deep-sea life, doesn’t make it past the twilight zone. So how does life exist this deep? If you’ve been paying attention, you probably know the answer. Deep-sea gigantism. At these depths, something normally the size of a gnat is as large as a guinea pig in comparison to its shallow water or land-dwelling counterparts. All of the advantages of gigantism are essential for the survival of these creatures.
One of the strangest creatures living in the deep is the Greenland shark. They are the only shark that can live in the Arctic year-round and the largest fish in the Arctic Ocean. As one of the largest shark species on earth, they can be around 22 feet long and weigh over 2,000 pounds. These sharks also live for an incredibly long time, up to 500 years, meaning some sharks were around when William Shakespeare was alive, or before the fall of the Aztec and Inca empires.
Despite all the research that has been done on our oceans, scientists still know next to nothing about the majority of its creatures. Just 5% of the ocean has been explored, and most of that was near the surface. We, truthfully, don’t know much about what's happening beneath the surface, but there’s no doubt that more discoveries about deep-sea gigantism are in store.
Deep-sea gigantism is the tendency for deep-sea creatures to be much larger than their shallow-water counterparts. Occurring mainly in invertebrates (animals without spines), the most notable examples are giant and colossal squids. However, this can also occur in crustaceans like the giant isopod. Fish—for example, the Greenland shark—are also products of this phenomenon. Some of the most colossal creatures in our oceans dwell in deep trenches and extreme conditions, causing exciting and frightening adaptations unlike anything we see on the surface. But why does this happen?
A thousand meters below the surface, no sunlight can penetrate the water. At this depth, no photosynthesis can occur, meaning that there are no plants available for animals to eat. Because of this, most of these animals have to rely on “marine snow.” It sounds pretty, but marine snow is actually detritus, or fine particles of dead organisms and fecal matter that rain down from shallow waters to the deeper parts of the ocean. Some animals sustain themselves solely on marine snow, but there isn’t enough to support all of the animals in the ecosystem. Instead, most animals don't eat marine snow, but instead prey on the creatures that do. This means that the smaller the animal, the bigger the target on their back. Size is a biological advantage, and the concentration of predators causes an extremely intense and competitive environment in the deep ocean.
However, size has another advantage. Essentially, the larger an organism is, the slower its metabolism works. Kleiber’s law states that the metabolic rate of an organism does not depend on animal size, but on animal mass. Instead of a 1:1 ratio, an animal's metabolic rate scales to the ¾ power of body mass. An exceptionally large organism could burn as low as 45 calories per day. With the pressure of predation and food scarcity, a large creature would need to hunt and eat less. For example, a giant squid's metabolism is so slow that it needs, on average, one ounce of food every day. The colossal squid is even heavier. A single adult toothfish would feed a colossal squid for about 200 days. Such a large size is an extreme advantage for this environment where food is so scarce.
The cold is another challenge these creatures have had to adapt to. Due to the lack of sunlight, the temperatures in the deep ocean are extremely low. The deepest zone in the ocean, the hadal zone, has average temperatures of just above freezing, around thirty two degrees fahrenheit. This unfriendly environmental temperature forces deep sea creatures to adapt to maintain their body heat in the extreme cold. This is another reason gigantism is advantageous. The more surface area an animal has, the more heat it loses. But a creature with a high body mass has a higher body mass to surface area ratio. In simple terms, the larger a creature, the less heat it will lose. This is an effective way to maintain body heat in such a challenging environment.
Most have heard of the Mariana Trench, the deepest spot in the ocean. At its deepest point, the Mariana trench is about 36,201 feet below sea level, or nearly 7 miles. The pressure can reach up to 1100 times the pressure of the surface, and there is no light. But 90% of marine snow, the backbone of deep-sea life, doesn’t make it past the twilight zone. So how does life exist this deep? If you’ve been paying attention, you probably know the answer. Deep-sea gigantism. At these depths, something normally the size of a gnat is as large as a guinea pig in comparison to its shallow water or land-dwelling counterparts. All of the advantages of gigantism are essential for the survival of these creatures.
One of the strangest creatures living in the deep is the Greenland shark. They are the only shark that can live in the Arctic year-round and the largest fish in the Arctic Ocean. As one of the largest shark species on earth, they can be around 22 feet long and weigh over 2,000 pounds. These sharks also live for an incredibly long time, up to 500 years, meaning some sharks were around when William Shakespeare was alive, or before the fall of the Aztec and Inca empires.
Despite all the research that has been done on our oceans, scientists still know next to nothing about the majority of its creatures. Just 5% of the ocean has been explored, and most of that was near the surface. We, truthfully, don’t know much about what's happening beneath the surface, but there’s no doubt that more discoveries about deep-sea gigantism are in store.