Life in the deep ocean

The ocean is divided into different regions based on the depth from the surface. As the depth increases the amount of sunlight decreases. In addition the pressure increases due to the sheer amount of water pressing down.

The first deep sea zone is called the mesopelagic zone, sometimes referred to as the twilight zone. The mesopelagic zone extends from ~660 feet to ~3300 feet below the surface. Although there is some light in this zone there is not enough sunlight available for photosynthesis. 

Bristle fish are the most abundant vertebrate on the planet. Estimates put bristle fish population in the thousands of trillions. Despite their sheer numbers little is known about the behaviour or the ecology of this fish.

Cephalopods like small cuttlefish and squid can be found in the mesopelagic zone. These animals have special jelly like tissue to help their bodies cope with the high pressure.

These fish have bioluminescent spots along their sides, lighting up the water. These fish can be found in such large numbers that sonars have attributed schools of them as land masses. 

These large fish are commonly found in the mesopelagic zone, only coming closer to the surface at night. A highly skilled predator they spend their time hunting smaller fish.

The Bathyal zone, sometimes referred to as the midnight zone extends from ~3300 feet to ~13,000 feet below the ocean surface. No sunlight penetrates this zone and the average temperature is around 39℉. Due to the absence of light many species do not have eyes. 

Although not as populated as the mesopelagic zone many animals can be found living in this region. 

This fish is sometimes referred to as a ‘living fossil’ and wasn’t discovered until 1879. It has 25 rows of teeth with 300 teeth in total. Scientists have yet to observe how this fish hunts. 

Some of the largest creatures on earth hunt within the bathyal zone. Sperm whales hunt giant squid (although this has never been observed by humans). They have a special oil filled pouch in their head believed to help them cope with the high pressure. 

The gulper eel has the unique ability to swallow prey far larger than itself. The eel’s mouth is much larger than its body. Once prey is captured it sits in a special pouch to slowly dissolve. 

Unlike other squid species the vampire squid cannot produce ink. When it needs to defend itself the squid lifts up its tentacles up over its head, exposing rows of spines. 

The abyssal zone extends from 13,123 feet to 19,685 feet below the ocean's surface. It is a zone with very few nutrients and perpetual darkness. The average temperature of this zone is 35℉. It is the deepest part of the ocean barring the deep sea trenches.

Ocean snow refers to all the decomposing matter that drifts down from shallower parts of the ocean. This debris, comprised of dead plants, algae, animals and their waste forms the base of the deep ocean food chain.

Although this part of the ocean remains quite cold there are areas which receive superheated water. Called hydrothermal vents these are openings where water heated from the Earth’s magma is released.

This little fish is only around 10 inches long but is able to swallow prey up to 30 inches long. Sometimes the decomposing prey causes a buildup of methane with will explode a hole in the swallower fish’s stomach. 

One of the deep sea’s most famous resident some species of the angler fish can be found in the abyssal zone. They use the bioluminescent growth on their head to lure in their prey.

The giant squid is famed in nautical history. These creatures can reach up to 43 feet in length and little is known about its behaviour or ecology. In fact only two videos of a live giant squid exist. 

The hadal zone is found within deep sea trenches, below the floor of the ocean. This zone extends from ~20,000 feet to ~36,000 feet. A surprising variety of life has been found living within this zone. 

Animals living at this depth need to contend with enormous pressure (the pressure would crush most submarines before it even reached this zone), no light and very little oxygen.

Amphipods are part of the crustacean family. These look like large fleas floating in the water. They feed on ocean snow (falling debris). 

The grenadier is one of the deepest living fish currently known to science. It feeds on amphipods and other small animals, moving slowly on the trench floor to conserve energy.

The enypniastes is a type of deep sea cucumber. It is unique among the sea cucumber family due to its extraordinary swimming capabilities (when compared to other sea cucumbers). It can also vomit out its digestive system when severely stressed. 

There are at least 10,000 species of bristle worms found in the ocean at varying depths, including in the hadal zone. The deep sea bristle worms can produce a variety of different bioluminescent colors. 

The Mariana trench is the deepest known part of the ocean on Earth. Located between Japan and Papua New Guinea it is 1,580 miles long and 43 miles wide. At its deepest point it is believed to be 36, 201 feet deep. 

This means if Mt Everest was placed in this part of the trench its peak would still be under a mile of water. Humans have only visited some parts of the trench four times. 

This fish has no scales and is the deepest known fish found on Earth. About 4 inches in length it has tiny eyes and large, fan like fins. 

The giant amphipod was discovered in the Mariana Trench. Usually found at sizes less than an inch the giant amphipod is 10 inches long.

Giant, single celled amoebas called xenophyophores were recorded during the 2011 expedition into the trench. These cells grow up to 4 inches in length.

Unlike what the name suggests the cusk eel is actually a fish, not an eel. Species from this family are found from near the surface all the way down into the Mariana Trench.

The deepest part of the ocean was first explored in the 1960s during the Challenger Deep expedition led by French scientist Jacques Piccard. The submarine holding two men delved down over seven miles under the ocean’s surface.

Due to the pressure the outer window cracked but the submarine held. The first exploration only spent 20 minutes on the floor of the Mariana Trench. The only other manned expedition was led by movie director James Cameron in 2012. 

This is the submersible that reached the Mariana Trench floor in 2012. Piloted by James Cameron the craft touched down at 35,756 feet. 

The Deepsea Challenger was designed in Sydney, Australia. Built using a specially developed foam called Isofloat which was created to withstand the enormous pressure that occurs in the deep sea.

It took the Deepsea Challenger two and a half hours to reach the bottom of the Mariana Trench. On board was a single passenger, movie director James Cameron.

During the record breaking three hour exploration the Challenger recorded tubeworms, giant amphipods and collected over 20,000 microbes for researchers to study.