Life in the Deep Sea

What is the Deep Sea?

The deep sea is the lowest layer of the ocean and is home to the most hostile conditions on Earth. There is no light, the pressure is extreme, and the temperatures are near freezing. But that is still not enough to stop life! Follow us as we dive into those waters and discover the amazing adaptationsadaptations of living beings in deep sea ecosystems.

How deep is the ocean really? This Incredible Animation Shows How Deep The Ocean Really Is

Did you know?

The deep sea takes up most of the space on the planet. This makes the deep-pelagic habitat the Earth׳s largest habitat by volume and the deep-benthic habitat the Earth’s largest habitat by area.

Who lives in the deep sea?

There are two types of deep-sea organisms:

• BenthicBenthic organisms are those that spend most of their lives on the ocean floor. Some benthic organisms, like lobsters and crabs, can freely move around on the ocean floor. Others, like anemones, attach themselves to the ocean floor. Examples of Benthic organisms in the deep sea include:
  • Yeti Crabs
  • Giant Tubeworms
  • Black Corals

• PelagicPelagicorganisms are those that spend their lives in the water itself. Pelagic fish actively swim in thewater columnwater column. Other organisms, likezooplanktonzooplankton, mainly just float around. Examples of Pelagic organisms in the deep sea include:
  • Whales
  • Giant Squid
  • Lantern Fish 

Explore the deep sea and the creatures that live in this ecosystem here!

How do Animals Survive in the Deep Sea?

Benthic and pelagic organisms survive hostile conditions in the deep sea. This is why they need special adaptations to find food, get around, withstand pressure and survive the cold. Let’s see just how they do it!

Finding Food

So how do animals find food so far underwater? Without sunlight andphotosynthesisphotosynthesis in the deep-sea, living plants are not available as food. Instead, deep-sea organisms feed on bits of dead plants, dead animals and animal wastes that fall from above. This food source is known as marine snow.

Another way that some microorganisms have adapted to find food in the deep sea is to create their own! Similar to the process of photosynthesis, these organisms convert energy from chemical reactions into nutrients. This process is called ChemoautotrophyChemoautotrophy..

Other fish are carnivorescarnivores. They lure in preyprey with their bioluminescent lures (see below). When this happens, deep-sea fish stretch their stomachs. This means they can eat organisms up to 3 times their own size! Also, once in a while, deep-sea scavengingscavenging animals get lucky when a whale carcass sinks to the bottom of the deep sea.

Adapting to Darkness

If you have been to the ocean or seen a film of the ocean, it may seem like a pretty bright place. But this is only the topmost layer of the ocean called the Sunlight Zone. Below around 200 metres it starts to get dark and the sunlight is too weak for any plants orphytoplanktonphytoplankton to survive. This zone is called the Twilight Zone and is the uppermost zone of the deep sea.

Most of the organisms that live in the twilight zone migrate up to the sunlight zone to feed at night. They then retreat to the safety of deeper waters before daybreak. This is called vertical migrationMost of the organisms that live in the twilight zone migrate up to the sunlight zone to feed at night. They then retreat to the safety of deeper waters before daybreak. This is called vertical migration.

In order to see in the darkness below 200 meters, some deep sea animals have very big eyes! Their highly light-sensitive eyes are adapted for sensing even the smallest amount of light. A good example is the Barreleye fish. But don’t be fooled, what looks like his eyes are body parts similar to nostrils. Its eyes are the round green balls within its transparent head.

Aside from big eyes, about 90% of the animals that live in the deep sea are bioluminescentbioluminescent. Bioluminescence is the ability of an animal to emit light. A group of bioluminescent land animals you might know are fireflies.

Bioluminescence is used by animals for a number of different purposes including:

• For communication;
• To scare off predators;
• To attract prey; and
• To attract potential mates.

Most bioluminescent fish produce a bluish-green light. These short wavelengthswavelengths of light can be most easily seen in both shallow and deep water. Longer wavelengths of light, such as red, cannot reach the deep ocean. This is why many deep sea animals are red. It makes them harder to spot!

Watch this video to learn about a fish that has adapted to produce red light!

Adapting to Pressure

Have you ever felt your ears pop when you swam to the bottom of a swimming pool? This is because the water and air above you creates pressure. The same thing happens in the ocean. The deeper you go in the ocean, the higher the pressure. Animals that live in these high pressure environments need to have some special adaptations.

Fish that swim in the Sunlight Zone usually have aswim bladderswim bladder filled with gas to control theirbuoyancybuoyancy. Fish control their ability to go up and down by controlling the amount of gas in their swim bladders.

When fish go down beyond the Sunlight zone, water pressure increases. This pressure squeezes the fish’s body including its swim bladder. The increased pressure on the gas in the bladder causes a decrease in volume. This is Boyle’s Law. With less volume keeping them up, fish would sink. So how do these fish go up and down? Some put more oxygen in their swim bladders, others use fats instead of gas to adjust their buoyancy. 

Whales Under Pressure

Did you know?

Some whales can dive down up to 3 000 metres. How do they do it?

Whales’ bodies are specially adapted for dealing with pressure changes. One way is that when squeezed by pressure, parts of their lungs can collapse. When this happens, air is squeezed out which minimizes the amount of nitrogen gas entering blood.

Having nitrogen gas in the blood is very dangerous when coming up after a dive. As whales swim upward, pressure decreases and gases expand. As it expands, nitrogen gas can form bubbles and end up in unwanted places like joints and the brain. This can cause pain, dizziness and fatigue. The term for this is decompression sickness, or “the bends.”

Crustaceans Under Pressure

Another pressure-related problem exists forcrustaceanscrustaceans. These animals haveexoskeletonsexoskeletons made of calcium carbonate. Scientists once believed crustaceans could not go deeper than about 4 kilometers because the pressure would crush their exoskeletons. But, scientists kept finding them at deeper and deeper depths, so why were they not being crushed?

One study of shrimp-like amphipodsamphipods living at the bottom of Challenger Deep found that these animals had a special layer of metal on their exoskeletons. These animals were sucking up aluminum-containing materials and mixing them with chemicals in their guts. This lets them produce an extra layer of metal armour!

Image - Text Version

Shown is a colour photograph of a small amphipod
This microscope image is of a tiny, pale pink, shrimp-like animal. Unlike a shrimp, it has a squat body and short antennas.

 

Adapting to the Cold

At an average temperature of 4 degrees celsius, the deep ocean is pretty chilly! Survival at such cold temperatures means that deep-sea creatures have developed certain adaptations including slowness. Deep sea creatures are usually sluggish. This means that they typically move and breathe very slowly. This is because their bodies have evolved to lower their energy needs.

We can actually see this adaptation by looking at certain deep-living creatures. Since they do not need as much energy, unnecessary features are not there. For instance, the record-holding snailfish has transparent skin, thin muscles, a skeleton made of cartilage and no scales! Its flesh is also made up of a jelly-like substance that is less dense than water. This way, it doesn’t need to swim to stop itself from sinking.

Other Adaptations

Scientists once thought that sunlight and oxygen were absolutely necessary to create life. But in 1977, scientists discovered an ecosystem in the ocean where animals lived without these things.

Scientists had been investigatinghydrothermalhydrothermalvents. These are cracks in the ocean floor where the Earth’scrustcrust opens to the hot, central layers of the planet. Water near these hydrothermal vents can reach 450 degree Celsius!

Near these vents on the ocean floor, they found a thriving community of organisms called extremophilesextremophiles. Extremophiles have unique adaptations that allow them to survive in the deep sea without food or oxygen. One example of an extremophile is the Giant Tubeworm. This was one of the Benthic organisms mentioned at the beginning.

Tubeworms don’t have a digestive system. Instead, scientists discovered that they contain bacteria in a special organ called the trophosome. Tubeworms and bacteria have a symbioticsymbiotic relationship. The tubeworm provides the bacteria a safe place to live. The bacteria uses minerals from the hydrothermal vents to create nutrients for the tubeworm.

It’s funny to think that scientists once believed the deep sea to have no life. In reality, the deep sea is the world’s largest habitat and is home to millions of species, many of which we have yet to discover!