Oceans cover more than two thirds of the world surface and contain a staggering 99% of the living space on our planet. It’s no surprise then that scientists are still turning up strange and unexpected creatures. We’ve all heard about the mysteries of the Bermuda Triangle and the strange adaptations of the Deep Sea, but what about life beneath millions of tons of ice and more than 800km from sunlight? Welcome to the hidden world beneath the Antarctic ice.
Antarctica’s glaciers and ice shelves extend hundreds of miles into the Southern Ocean. In places, they are nearly a mile thick. Being so remote and inhospitable, scientists have long assumed the ocean floor beneath the ice to be barren and devoid of life. With no sunlight, very little nutrients and bitter cold, what could possibly survive?
The only difficulty was that no one had ever checked. You either have to dig down through hundreds of metres of ice, or send a submersible on a long and perilous journey, both of which pose substantial technical challenges. That was until last year, when a team of scientists studying the Ross Ice Shelf successfully managed to lower a small underwater vehicle down a narrow borehole to collect sediment samples. To their surprise they found life surviving in a tiny strip of water barely 10 meters deep, sandwiched between a monstrous ice shelf above and the bleak ocean floor. With more research, some strange and unexpected adaptations are emerging from the creatures that call this place home.
The first challenge is that water temperatures can be as low as -2ºC (dissolved salts lower the freezing temperature of sea water below zero). To survive this, some species of fish have evolved a protein that acts as an antifreeze to protect their blood and body fluids. Scientists call this clever evolutionary strategy ‘cryoprotection’.
Another striking characteristic of the fish seen beneath the ice is that they often have translucent bodies. This is probably because unlike many other animals, their blood has lost most of its haemoglobin, which helps transport oxygen around the body. They still survive because waters beneath Antarctica are extremely rich in oxygen, and at cold temperatures it dissolves in to the blood plasma much more readily. Without pigmented blood, it’s sometimes possible to see organs and bones within the bodies of these mysterious fish.
One particularly menacing group found in these waters are the Channichthyidae, imaginatively known as the crocodile icefish. These are ambush predators that can consume as much as 50% of their bodyweight in one sitting. But impressive though they sound, in the cold waters of Antarctica they barely grow beyond 50cm long. It’s not just fish that have been found either; strange new species of sea anemone have been photographed hanging upside-down from the bottom of ice shelves. What they eat, let alone how they can survive remains a mystery.
So whilst these far reaches of the ocean have many more treasures waiting to be discovered, what does the future hold for Antarctica’s unexpected inhabitants? Surprisingly, scientists are concerned about a growing threat from climate change. Ocean temperatures are rising, and the melting of Antarctic ice shelves appears to be accelerating, both factors that may disrupt the delicate balance of life under the ice. Worryingly, research suggests that fish without haemoglobin are likely to be more vulnerable to increases in temperature. So the adaptations that have allowed these species to survive, might just be their downfall.
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