Life in the world’s deepest oceans a spectacular and fragile struggle for survival

Cloaked in darkness and mystery, the creatures of the deep oceans exist in a world of unlikely profusion, surviving on scant food and under pressure that would crush human lungs.

This hostile environment, which will come under the spotlight at a major United Nations oceans summit in Lisbon this week, has caused its inhabitants to develop a prodigious array of alien characteristics and idiosyncratic survival techniques.

A vast assortment of animals populate the sunless depths, from the colossal squid, which wrapped its tentacles around the imaginations of sailors and storytellers, to beings with huge cloudy eyes, or whose bodies are as transparent as glass.

And the angler fish, with its devilish looks illuminated by a built-in headlamp, showing that the deep dark is alive with lights.

Until the middle of the 19th century, scientists believed that life was impossible beyond a few hundred metres.

“They imagined that there was nothing, because of the absence of light, the pressure, the cold, and the lack of food,” said Nadine Le Bris, a professor at Sorbonne University.

Between 200 and 1,000 metres, the light fades until it vanishes completely, and with it plants; at 2,000 metres the pressure is 200 times that of the atmosphere.

From the abyssal plains to the cavernous trenches plunging deeper than Everest is high, aquatic existence continues in spectacular diversity.

“When people think of the deep sea they often think of the sea floor,” said Karen Osborn of the Smithsonian’s Natural History Museum. “But all that water in between is full of incredible animals. There is a ton of life.”

These open water inhabitants face a formidable challenge: they have nowhere to hide.

“There’s no seaweed to hide in, no caves or mud to dig into,” Osborn said. “There are predators coming at them from below, from above, from all around.”

One tactic is to become invisible. Some creatures are red, making them difficult to distinguish in an environment where red light no longer filters through.

Others render themselves transparent. Take the transparent gossamer worm, which ranges in size from a few millimetres to around a metre long and shimmies through the water by fluttering its frilly limbs.

“They look like a fern frond,” Osborn said. “They’re beautiful animals and they shoot yellow bioluminescent light out of the tips of their arms. What could be better than that.”

With no plants around and animals scattered in the vastness doing their utmost to disappear, creatures in the ocean depths often have a hard time finding a live meal.

“If you happen to get lucky and hit a patch of your food, bingo! But you may not see another one for three weeks,” Osborn said.