The Deep Sea Ecosystem

Over 60% of our planet is covered by water more than a mile deep. The deep sea is the largest habitat on earth and is largely unexplored. More people have traveled into space than have traveled to the deep ocean realm.... - The Blue Planet Seas of Life

The benthic and abyssal zones are where the cold, dark, deep waters of the ocean are found. These zones are the largest part of the ocean biome covering more than 80% of the vast ocean. The intertidal zone where the water meets land and the pelagic zone, or open ocean, make up a much smaller portion of the total area of the ocean, yet an abundance of ocean life is found in these zones because sunlight penetrates the water. To get an idea of how vast the ocean's depths are, consider that 79% of the entire volume of the earth's biosphere consists waters with depths greater than 1,000 m. Until recently, the deep sea was largely unexplored. 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.

Deep sea research is vital because this area is such an enormous part of the biosphere. Despite its depth and distance, it is still our backyard. There may be life-altering discoveries found at the bottom of the ocean.

The zone beneath the pelagic zones is the benthic zone and is defined as the lowest level of a body of water such as an ocean or a lake, and includes the bottom sediments. Organisms living in this zone are called benthos . They generally live in a close relationship with the bottom of the sea; with many of them permanently attached to it. In oceanic environments, benthic habitats can be further zoned by depth. From the shallowest to the deepest are: the epipelagic (less than 200 meters), the mesopelagic (200– 1000 meters), the bathyal (pelagic) (1,000–4,000 meters), the abyssal (pelagic) (4000–6,000 meters) and the deepest, the hadal (pelagic) (below 6,000 meters). The abyssal zone is found beneath the benthic zone, extending down to the deepest depths of the ocean, which are about 33,000 feet deep. Deep sea thermal vents can be found in this zone. The hadal zone is used to define the waters of the deep sea trenches.

Exploration of these zones has presented a challenge to scientists for decades and much remains to be discovered. However, advances in technology are increasingly allowing scientists to learn more about the strange and mysterious life that exists in this harsh environment. Life in the deep sea must withstand total darkness, extreme cold, and great pressure. To learn more about deep-sea marine life, sophisticated data collection devices have been developed to collect observations and even geological and biological samples from the deep. Advances in observational equipment such as fiber optics that use LED light and low light cameras has increased our understanding of the behaviors and characteristics of deep sea creatures in their natural habitat. Remotely operated vehicles (ROVs) have been used underwater since the 1950s. ROVs are basically unmanned submarine robots with umbilical cables used to transmit data between the vehicle and researcher for remote operation in areas where diving is constrained by physical hazards. ROVs are often fitted with video and still cameras as well as with mechanical tools for specimen retrieval and measurements. Manned deep sea submersibles are also used to explore the ocean's depths. Alvin is a deep sea submersible built in 1964 that has been used extensively over the past 4 decades to shed light on the black ocean depths. This sub has been used for more than 4,000 dives reaching a maximum depth of more than 4,500 m.

Physical Characteristics of the Deep Sea

The physical characteristics of the deep sea are abiotic factors that deep sea life must contend with to survive. Light, pressure, temperature, oxygen and food have all led to the fascinating adaptions of deep sea life used to see, feel, feed, reproduce, move, and avoid being eaten by predators.

Light The deep ocean waters are as black as night. The deep is also known as the twilight zone. The only light is produced by bioluminescence, a chemical reaction in the creature's body that creates a low level light, so deep sea life must rely on alternatives to sight. Many deep sea fish have adapted large eyes to capture what little light exists. Most often, this light is blue-green, but some creatures have also developed the ability to produce red light to lure curious prey. Lack of light also creates a barrier to reproduction. Bioluminescent light is also used to signal potential mates with a specific light pattern. Deep sea creatures are also often equipped with a powerful sense of smell so that chemicals released into the water can attract potential mates.

Pressure Considering the volume of water above the deepest parts of the ocean, it's no wonder that pressure is one of the most important environmental factors affecting deep sea life. Pressure increases 1 atmosphere (atm) for each 10 m in depth. The deep sea varies in depth from 700 m to more than 10,000 m, therefore pressure ranges from 20 atm to more than 1,000 atm . On average, pressure ranges between 200-600 atm . Advances in deep sea technology have enabled scientists to collect species samples under pressure so that they reach the surface for study in good condition. Without this technology, the animals would die shortly after being collected and the absence of pressure would cause their organs to expand and possibly explode. With good samples, we now know that deep sea creatures have adapted to pressure by developing bodies with no excess cavities, such as swim bladders, that would collapse under intense pressure. The flesh and bones of deep sea marine creatures are soft and flabby, which also helps them withstand the pressure. Temperature The difference in temperature between the photic, or sunlit, zones nearer to the surface and the deep sea are dramatic. Temperatures vary more in the waters above the benthic zone where thermoclines, or the separation of water layers of differing temperatures, are more common. In most parts of the deep sea, the water temperature is more uniform and constant. With the exception of hydrothermal vent communities where hot water is emitted into the cold waters, the deep sea temperature remains between 2- 4°C .

Oxygen The dark, cold waters of the deep are also oxygen- poor environments. Consequently, deep sea life requires little oxygen. Oxygen is transported to the deep sea from the surface where it sinks to the bottom when surface temperatures decrease. Most of this water comes from Arctic regions. Surprisingly, the deep sea is not the most oxygen-poor zone in the ocean. The oxygen minimum zone lies between 500-1,000 m, where there are more species that require oxygen, depleting the oxygen in this zone during respiration. In addition, the bacteria that feed on decaying food particles descending through the water column also require oxygen. Oxygen is never depleted in the deepest parts of the ocean because there are fewer animals to deplete the available oxygen.

Food Deep sea creatures have developed some fascinating feeding mechanisms because of the lack of light and because food is scarce in these zones. Some food comes from the detritus, of decaying plants and animals from the upper zones of the ocean. The corpses of large animals that sink to the bottom provide infrequent feasts for deep sea animals and are consumed rapidly by a variety of species. The deep sea is home to jawless fish such as the lamprey and hagfish, which burrow into carcasses, quickly consuming them from the inside out. Deep sea fish also have large and expandable stomachs to hold large quantities of scarce food. They don't expend energy swimming in search of food, rather they remain in one place and ambush their prey using amazing and clever adaptations.

Adaptations of deep-sea organisms Some of the most fascinating and amazing characteristics of deep sea creatures are the adaptations they have developed to survive the harsh environment. We've briefly covered adaptations such as large eyes, bioluminescence, strong sense of smell, body composition (absence of swim bladder), expandable stomachs, absence of jaws, and bioluminescence. Color is another adaptation developed for camoflauge and protection from predators. Deep sea fish are often transparent, black, silvery and even red in color. The absence of red light at these depths keeps them concealed from both predators and prey.

Adaptations have also evolved to capture prey. In addition to their large mouths, deep sea fish, such as the deep sea anglerfish, often have extremely long teeth that point inward. This ensures that any prey captured has little chance of escape. Deep sea species such as the gulper eel have huge hinged jaws, which enables them to swallow large prey. Some deep sea species, such as the deep sea anglerfish and the viperfish, are also equipped with a long, thin modified dorsal fin on their heads tipped with a photophore lit with biolumenescence used to lure prey.

Deep sea anglerfish have an interesting reproductive adaptation. Males are tiny in comparison to females and attach themselves to their mate using hooked teeth, establishing a parasitic 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 very reliable sperm source.

Hydrothermal Vent Communities

Life in the deep sea is relatively sparse in the deep sea compared to the intertidal zone, with one exciting, and recently discovered exception - hydrothermal vent communities. This surprising discovery occured in 1976 during a deep sea expedition in Alvin near the Galapagos. These dives to depths of about 2,700 m led to the discovery of this remarkable ecosystem where marine life flourished at deep depths in the absence of sunlight.

Hydrothermal vent communities are found at depths ranging from 1,500-3,200 m. The water temperature near these communities is much warmer than is normal for this depth (about 2°C ), averaging between 8-16°C . The hot mineral-rich water comes from geysers in the seafloor heated by magma beneath the earth's crust. These vents are most commonly found near mid-ocean ridges where the sea floor is spreading due to the movement of ocean plates. Metal sulfides expelled through the vents settle and form chimneys around which are soon populated by a variety of sea life. Soon after hydrothermal vents were discovered, the communities of giant tube worms that inhabit them were also discovered. In the absence of sunlight, these worms, known as chemoautotrophs, subsist on hydrogen sulfide found in the warm waters surrounding vent communities. The hydrogen sulfide is turned into energy by bacteria that live inside the worms. Deep sea fish is a term for any fish that lives below the photic zone of the ocean. The lanternfish is, by far, the most common deep sea fish. Other deep sea fish include the flashlight fish, cookiecutter shark, bristlemouths, anglerfish, and viperfish. Humpback anglerfish

Deep Sea Hydrothermal Vents

Giant Tube Worms Near a Deep Sea Hydrothermal Vent. In the late 1970's, scientists on a routine study of the ocean floor in the Pacific made a discovery that would rock the entire scientific community. On the East Pacific Rise not far from the Galapagos Islands, nearly 8000 feet below the surface, was a strange alien landscape littered with what looked like chimneys expelling clouds of black smoke. Surrounding these chimneys was a unique type of ecosystem that had never been seen before. Until this day, science had always assumed that all life on Earth obtained its energy from the Sun. The plants convert sunlight into energy through a process called photosynthesis. The plants, in turn, provide food for countless species of animals in a complex web of life. But here, facing the deep-sea submersibles, was a sight that challenged those assumptions. Here was proof for the first time that life could be sustained by the Earth itself. Black Smoker on the ocean floor. Science had discovered deep-sea hydrothermal vents. These vents occur in geologically active regions of the ocean floor. Within these regions, seawater seeps down deep into the Earth's crust through cracks and fissures in the ocean floor. This water is then heated by magma below the surface. As the water is heated to a boil, it expands and rises back to the surface. On it's way back up through the cracks and fissures through which it fell, the hot water dissolves minerals and other chemicals from the rock. When it reaches the ocean floor, the water is a dark, chemical soup. Some of the minerals precipitate out of the seawater and harden on the rim of the vent. Over time, the rim of the vent is built up into a tall, chimney-like structure. The dark color of the water spewing forth from these vents has earned them the name, "black smokers". The temperature of the water coming out of these vents exceeds 360º. The real surprise was the discovery that a myriad of life forms actually live and thrive around these vents, totally cut off from the world of sunlight.

Large Crab and Clams Near a Deep Sea Hydrothermal Vent.

Incredible deep-sea creatures have been known for quite some time. But these animals all depended on the regions above for their sustenance. They feed on small scraps of food and dead animals that fall from above. Here at the vents, though, something entirely different was taking place. These organisms were getting their food directly from the vents themselves. This process is known as chemosynthesis. Bacteria in the water actually feed on what would otherwise be a lethal soup of noxious chemicals. Smaller animals feed on these bacteria, and these smaller animals provide food for the larger animals. It is an entire ecosystem totally separate from the world of light. A large number of strange and wondrous creatures have been found at these vent sites. Giant tube worms eight feet tall dominate the landscape. Tiny bacteria living inside make food for the worms. Small shrimps and crabs feed on the tube worms. Clams cover the ocean floor. These waters are so fertile that shrimps have been known to literally number in the millions near these vents. Deep Sea Creature Atlantic Hagfish Coelacanth Chambered Nautilus Deep Sea Anglerfish Deep Sea Dragonfish Fangtooth Firefly Squid Giant Isopod Giant Squid Giant Tube Worm Gulper Eel Hatchetfish Lanternfish Oarfish Sixgill Shark Snipe Eel Sperm Whale Vampire Squid Viperfish Bioluminescence Layers of the Ocean Hydrothermal Vents Credits and References

Coming Soon: Atlantic Footballfish Bristlemouth Colossal Squid Fanfin Anglerfish Frilled Shark Goblin Shark Long-nosed Chimaera Stoplight Loosejaw Swallower Eel Tripod Fish Tube-eye Wolftrap Angler