Strange creatures of the ocean deep

Oceans are home to most of the planet's flora and fauna. Even at incredible depths of around 1000 meters (3,300 feet) and more, where the sea is perpetually dark and the pressure of freezing water would be unbearable for humans, animals manage to thrive.

Deep sea creatures have evolved to deal with the difficult conditions — and can seem weird and even terrifying to humans. Global Ideas takes a look at a few of those strange underwater beings and their adaptations.

Let there be light

The only light that exists in the ocean's midnight (1,000 meters to around 4,000 meters) and lower midnight (4,000 meters to above the ocean floor) zones comes from bioluminescent organisms. These creatures produce their own light through a chemical reaction that occurs when the molecule luciferin reacts with oxygen.

Animals create their own light for a variety of reasons. For instance, the cranky-looking anglerfish lures its prey with a luminous rod that juts out from its head. The light also helps the anglerfish and other glowing animals to get a better look at their lunch. Much of that food — mainly organic matter — rains down from the life-filled zones above where the sun's rays filter through the water and photosynthesis occurs.

Read more: Bioluminescence — Why plankton glows

Marine animals in the midnight zones use bioluminescence to attract mates or to denote the difference between male and females. In the case of anglerfish, only females have a luminous rod. Rather than constantly having to search the depths for a mate, the much smaller male will latch onto a female, eventually physically fusing with her, losing his eyes and internal organs except his testes in the process, writes National Geographic.

Under pressure

At a depth of around 2000 feet, pressure is 66 times greater than on the ocean's surface. A person would be crushed under that weight. (The record for the deepest human scuba dive is 332.35 meters and that required four years of preparation.)

But animals at home in the deep sea can withstand bone-breaking pressure — in some cases because they don't really have a skeleton. Deep sea creatures, like the unfortunately named blobfish, have weak and watery muscles that cannot be compressed. Others have no air cavities. This prevents "the squeeze" experienced by human divers, for instance, in lungs and other air-filled spaces in the body.

Read more:  Bug-eyed colossus

Animals that generally live on the surface but dive to great depths in the search of food have also developed features to deal with the squeeze. The lungs of sperm whales collapse compress to prevent rupture. The tissue lining of other air cavities in their bodies also expands during a dive to prevent damage.

The Mariana Trench is the deepest part of the world's oceans. The peak of Mount Everest would lie 1.6 kilometers under the water's surface if it were dropped here. And it is here that the pressure is at its greatest — the equivalent of the weight of 48 Boeing 747 jets. Still, some invertebrates, such as starfish, sea cucumbers and tube worms, can live happily at these depths.

Secrets of the deep

Scientists still know very little about the kinds of animals living at the earth's deepest point but have recently discovered new species thanks to advances in deep-diving vehicles, 3D cameras and scientific sampling equipment. This progress has allowed us to catch glimpses of unimaginable marine life in Earth's largest and least explored habitat. 

In 2014, the Schmidt Ocean Institute found an unknown variety of snailfish living at 8,143 meters. The white translucent creature is the deepest living fish ever recorded. It has since been captured swimming even further down.