Ten Marine Species That Thrive In Extreme Cold
Although as divers we spend much of our time on warm, tropical reefs, the ocean’s chilly depths are home to lots of interesting creatures as well, as are the Arctic and Antarctic landscapes. Here are 10 species that have adapted well to the extreme cold of our planet’s furthest reaches.
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Opah
Found in the deep waters of most oceans, the opah is no stranger to temperatures lower than 39 degrees F (4 C). To cope with such frigid conditions, this fish has a counter-current heat-exchange system in its gill tissue, which allows it to maintain a body temperature that exceeds the temperature of the surrounding water by approximately 41 degrees F (5 C). The opah is therefore warm-blooded, which makes it unique amongst fish species and allows it to remain active even in near-freezing water.
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Emperor Penguin
The tallest and largest of all penguins, the emperor is found exclusively in the Antarctic. There, the water temperatures remain around the freezing point for saltwater, a frigid 28.8 F (1.8 C). To cope with the Antarctic weather, emperor penguins have the highest feather density of any bird species, with around 100 feathers covering one square inch of skin. In the water, these feathers flatten to create a waterproof outer layer, which protects the penguins’ insulating down from becoming saturated with cold water.
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Greenland Shark
Greenland sharks are the only true sub-Arctic shark species, and have been observed at depths of up to 7,200 feet (2,200 m). They are able to survive the near freezing temperatures of these waters thanks to a compound called trimethylamine oxide, which acts as a natural anti-freeze and prevents ice crystals from forming in the sharks’ bloodstream. This compound also makes Greenland shark meat poisonous to humans and other mammals, so this species has no natural predators.
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Bowhead Whale
Thought to live exclusively in and around the waters of the Arctic Circle, the bowhead whale has blubber that’s approximately 20 inches (50 cm) thick, the thickest of any animals’. The bowhead also has a massive, bony skull that it uses to break through the ice when it surfaces to breathe. This species has an incredibly slow metabolism, which helps it to conserve energy in the cold, and which is also thought to explain its lifespan of more than 200 years.
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Antarctic Sea Spider
Like all marine invertebrates, sea spiders have a body composition that matches the salinity of the ocean, which means that as long as the water around them remains in liquid form, they cannot freeze. Antarctic sea spiders are considerably larger than temperate sea spiders, having an average leg span of 29.5 inches (75cm) in comparison to the .78-inch (2cm) leg span of their warm-water relatives. It is thought that this polar gigantism occurs as a result of the heightened levels of oxygen found in cold water.
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Crocodile Icefish
The blood of the crocodile icefish does not contain hemoglobin and is completely colorless, a unique mutation that has both advantages and disadvantages. On one hand, the animal’s blood transports just 10 percent of the oxygen it could transport if the fish had hemoglobin, but on the other, the waters of the Antarctic are exceptionally rich in oxygen, meaning that the icefish survives despite this reduced capacity. The absence of hemoglobin makes the icefish’s blood thinner, allowing for a slower metabolism, which in turn helps the animal to conserve energy.
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Polar Bear
As the world’s largest marine mammal, the polar bear is perfectly adapted to the frigid temperatures of its Arctic home. Polar bears’ main defense against the cold is an insulating layer of blubber, which can be up to 4 inches (10 cm) thick when measured in conjunction with their thick hide and fur. Like the emperor penguin’s feathers, the polar bear’s fur comprises two layers for extra insulation, one of dense underfur, and one of coarse, transparent guard hairs.
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Tardigrade
Also known as water bears, tardigrades are microscopic animals found in some of the world’s most extreme environments, including the deepest ocean trenches and under thick sheets of ice. They are able to withstand exposure to absolute zero temperatures, i.e. -458 °F (-272 C). Tardigrades survive by replacing most of their internal water with the sugar trehalose, which prevents it from crystalizing and damaging cell membranes. They are able to reversibly suspend their metabolism, in a phenomenon known as natural cryopreservation.
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Antarctic Toothfish
The Antarctic toothfish produces anti-freeze glycoproteins that prevent ice crystals from forming in its bloodstream. This is an adaptation to its subzero habitat, one that’s absent in its close relative, the warm-water Patagonian toothfish. The Antarctic toothfish is a voracious predator, and can exceed 6.6 feet (2 m) long. This species has well-developed eyesight and a sensitive lateral line, which helps it detect prey even in the low-light conditions caused by permanent ice-cover.
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Weddell Seal
With the most southerly distribution of any mammal, the Weddell seal is no stranger to the cold. They are also the only mammals to overwinter in the Antarctic, and therefore experience some of the harshest conditions on Earth. Weddell seals survive the winter by taking to the water and living beneath the ice, where they are sheltered from the season’s bitterly cold blizzards. The seals maintain breathing holes in the ice, keeping them open by dragging their teeth from side to side along the holes’ frozen edges.
