It is important to realize that photosynthesis occurs only down to about 100 – 200 m, and sunlight disappears altogether at 1,000 m or less. While the ocean descends to a maximum depth of about 11,000 m in the Mariana Trench, the deep seafloor is, on average, 4,000 m below the ocean’s surface. There is remarkably little known about the deep ocean, in fact, we know more about the surface of the moon than we do about the ocean floor and its surprising diversity of bottom dwelling creatures. So, in a sense, a majority of the creatures lurking below the surface may as well be aliens. Researchers from Dalhousie University in Nova Scotia, Canada, believe that 91 percent of them are still unknown. But advances in deep sea submersibles and image capturing and sampling technologies are increasing the opportunities for marine biologists to observe and uncover the mysteries of the deep ocean realm. Most deep-sea animals do not look or act like their cousins closer to the surface. Their unusual body shapes, colors and behaviors may seem strange, but adaptations help them to survive in this challenging habitat.
Unlike animals on land or in shallow water – where skin, fur, and feather coloration may differ within habitats like hues on an artist’s palette – deep-sea animals must withstand total darkness (except for non-solar light such as bioluminescence), extreme cold, and great pressure. To adapt, they follow a surprisingly regular pattern in their coloration. At greater depths, animals are generally transparent, but have red stomachs. Below that, animals are red or black over their entire bodies. Finally, at the bottom, almost all animals are either a pale red or a cream color. The most likely explanation for this distribution is camouflage. Reproductive adaptation is another unique adjustment that animals of the deep-sea have evolved to cope with their harsh environment. Consider how hard it must be to find a mate in the vast dark depths. For most deep-sea species, scientists still do not know how they achieve this. Deep-sea anglerfish may use such light patterns as well as scents to find mates. Male anglerfish are tiny in comparison to female and attach themselves to their mate using hooked teeth, establishing a parasitic-like relationship for life. The blood vessels of the male merges with the female’s so that he receives nourishment from her. In exchange, the female is provided with a reliable sperm source, avoiding the problem of having to locate a new mate every breeding cycle. Another possible adaptation that is not fully understood is called deep-sea gigantism. This is the tendency for certain types of animals to become truly enormous in size. A well-known example is the giant squid, but there are many others such as the colossal squid, the giant isopod, the king-of-herrings oarfish, and the recently captured giant amphipod from 7,000 m in the Kermadec Trench near New Zealand.
Creatures that live thousands of feet below the ocean’s surface have developed special adaptabilities to survive. They have captured our imagination for centuries and for good reason. Once the zone where light penetrates the ocean is ventured, the dark depths of the sea are filled with strange and captivating critters, some of which have even inspired horror movie monsters.
Faceless cusk eel
As the name suggests, the faceless cusk eel has no face. The fish only recently gained its creepy name from its lack of distinguishable eyes, eye-like nostrils, and its mouth sits underneath the rest of its body, and is “protrusible,” meaning it extends to catch food, and then disappears back inside of its own body. Although the faceless cusk’s snake-like shape resembles that of an eel, the strange, deep-sea animal is a true fish. The animal is closely related to the similarly serpentine pearlfish.
The vampire squid
With scientific name, Vampyroteuthis infernalis, means “vampire squid from hell” very little is known about this mysterious creature that is thought to reside at lightless depths of up to 900 m. Here the saturation of oxygen may be as low as 3%, but the vampire squid is easily able to thrive in these suffocating conditions. The animal is not technically a squid or an octopus, but it is closely related to the two. And while the vampire squid does not actually drink blood, its dark red color and cape-like flaps do suggest the animal took a page out of Bram Stoker’s Dracula. The vampire squid is relatively tiny, reaching a maximum of 6 inches in length. It gets its name from its red coloring, glowing, bioluminescent eyes and the cloak-like webbing that connects its eight arms.
Look like glowing mini jellyfish, these bioluminescent sea creatures create their own light in the darkness. They either live solitary lives or in colonies and eat through filter-feeding.
The anglerfish is most famous for the bioluminescent growth on its head. Just like in Finding Nemo, the deep-sea varieties of anglerfish have nightmarish mouths filled with long, fanged teeth. Their characteristic mode of predation is by using a fleshy growth from their head as a fishing lure, waving it back and forth to attract pray. The jaws and bodies of anglerfish are highly expandable, meaning they are able to swallow prey up to twice their own size.
Covered in black, velvety skin is this eel-like monster, which resides in the darkness of the ocean 3,000 m below the surface. Also known as the pelican eel, it is one of the strangest looking fish in the sea. Its mouth is disproportionately large for its body and can open wide to consume animals much larger than the eel itself, similar to how a pelican used its large beak. Like the anglerfish, the gulper eel has a bioluminescent organ that scientist theorizes could be used to attract prey.
Ghost shark or Chimaera.
Little is known about chimaeras, which were only filmed recently in their natural habitat for the first time. Chimera lives at depths of 8,200 feet or more. There are about 47 species, which range in length from 24 to 80 inches. Archaeological evidence has proven that chimera have been around for millions of years. The earliest fossil specimen, a skull, was dated to about 280 million years ago. It was unearthed in South Africa in the 1980s.
Also known as a spook fish, the barreleye has extremely light-sensitive eyes on the top of its fluid-filled head. This futuristic-looking fish is named for its barrel-shaped, tubular eyes that are enclosed within a large, transparent dome of soft tissue. The barreleye was first described in 1939, but remained a mystery to scientists until 2009, when they discovered that its large, tubular eyes could actually rotate inside of its head. This rotational ability allows them to look upward for potential prey or face forward to see what it is eating. Since barreleyes live at depths where there is hardly any light, their tubular eyes help them use whatever faint amounts of light drift down to them. They also have two spots above their mouths which are called nares, analogous to human nostrils.