Deep-sea community
Deep sea communities remain largely unexplored, due to the technological and logistical challenges and expense involved in visiting this remote biome.
Because of the unique challenges (particularly the high barometric pressure, extremes of temperature, and absence of light), it was long believed that little life existed in this hostile environment.
The three main sources of energy and nutrients for deep sea communities are marine snow, whale falls, and chemosynthesis at hydrothermal vents and cold seeps.
In the 1870s Sir Charles Wyville Thomson and colleagues aboard the Challenger expedition discovered many deep-sea creatures of widely varying types.
The first discovery of any deep-sea chemosynthetic community including higher animals was unexpectedly made at hydrothermal vents in the eastern Pacific Ocean during geological explorations (Corliss et al., 1979).
[1] Two scientists, J. Corliss and J. van Andel, first witnessed dense chemosynthetic clam beds from the submersible DSV Alvin on February 17, 1977, after their unanticipated discovery using a remote camera sled two days before.
The depression is named after HMS Challenger, whose researchers made the first recordings of its depth on 23 March 1875 at station 225.
The Japanese remote operated vehicle (ROV) Kaiko became the second vessel to reach the bottom of the Challenger Deep in March 1995.
Photosynthesis in turn requires energy from sunlight to drive the chemical reactions that produce organic carbon.
Any life forms present in the aphotic zone must either be capable of movement upwards through the water column into the photic zone for feeding, or must rely on material sinking from above,[5] or must find another source of energy and nutrition, such as occurs in chemosynthetic archaea found near hydrothermal vents and cold seeps.
With the advent of traps that incorporate a special pressure-maintaining chamber, undamaged larger metazoan animals have been retrieved from the deep sea in good condition.
The limited amount of light, however, can still allow organisms to see, and creatures with a sensitive vision can detect prey, communicate, and orientate themselves using their sight.
The swimbladder is inflated when the fish wants to move up, and, given the high pressures in the mesopelagic zone, this requires significant energy.
However, some of these predators have yellow lenses that filter the (red deficient) ambient light, leaving the bioluminescence visible.
[24] Fish find it hard to live in this zone, as there is crushing pressure, cold temperatures of 4 °C (39 °F), a low level of dissolved oxygen, and a lack of sufficient nutrients.
[20]: 585 What little energy is available in the bathypelagic zone filters from above in the form of detritus, faecal material, and the occasional invertebrate or mesopelagic fish.
[25] The fish that do live there may have reduced or completely lost their gills, kidneys, hearts, and swimbladders, have slimy instead of scaly skin, and have a weak skeletal and muscular build.
[23] The only organisms that inhabit this zone are chemotrophs and predators that can withstand immense pressures, sometimes as high as 76 megapascals (750 atm; 11,000 psi).
The deepest point in the hadal zone is the Marianas Trench, which descends to 10,911 metres (35,797 ft) and has a pressure of 110 megapascals (1,100 atm; 16,000 psi).
They have special adaptations for this extreme environment: rapid growth, effect larval dispersal mechanism and the ability to use a 'transient' food resource.
Sometimes sudden access to nutrients near the surface leads to blooms of plankton, algae or animals such as salps, which becomes so numerous that they will sink all the way to the bottom without being consumed by other organisms.
These short bursts of nutrients reaching the seafloor can exceed years of marine snow, and are rapidly consumed by animals and microbes.
The waste products becomes part of the deep-sea sediments, and recycled by animals and microbes that feed on mud for years to come.
Whale fall community progresses through three stages:[32] Hydrothermal vents were discovered in 1977 by scientists from Scripps Institution of Oceanography.
So far, the discovered hydrothermal vents are all located at the boundaries of plates: East Pacific, California, Mid-Atlantic ridge, China and Japan.
This source of energy creates large populations in areas around hydrothermal vents, which provides scientists with an easy stop for research.
[35] Hydrothermal vents are entire ecosystems independent from sunlight, and may be the first evidence that the earth can support life without the sun.
Between 1991 and 2016, 242 unique feeding relationships between 166 species of predators and prey demonstrated that gelatinous zooplankton have an ecological impact similar to that of large fishes and squid.
Narcomedusae, siphonophores (of the family Physonectae), ctenophores, and cephalopods consumed the greatest diversity of prey, in decreasing order.
Humans have explored less than 4% of the ocean floor, and dozens of new species of deep sea creatures are discovered with every dive.
