Deep Sea Adaptation

Deep Sea Adaptation:

The deep sea is the largest habitat on earth and is widely unexplored. The deep sea is the lowest layer in the ocean below the thermocline and above the seabed. Of the estimated 500,000 to 10 million species living in the deep sea, most are yet to be discovered, and 98% of these species live in, on or just above the floor of the sea. There is a vast variety of creatures living in the ocean; 28 major groups of animals living in the sea verse only 11 major groups of animals live on land. These organisms have had to adapt to severe conditions of immense pressure, total darkness, limited oxygen, extreme temperatures, and inadequate nutrients. Although, these organisms have found unique and fascinating adaptations to thrive in such a harsh environment for instance bio-luminescence, flexible bodies, and massive unhinged jaws with large expandable stomachs. 

Ocean Zones

 The oceans are divided into two major zones; pelagic and benthic. Pelagic is the open sea consisting of everything in the ocean outside of coastal areas in which swimming and floating organisms live. The pelagic zone is separated into epipelagic, mesopelagic, bathypelagic, abyssopelagic and hadapelagic sub-zones. Areas in the pelagic zone are distinguished by their depth and the ecology.

Epipelagic Zone:

The epipelagic zone is less than 200 meters from the surface, where photosynthesis can occur. This zone is full of flourishing life due to the sunlight that penetrates the surface. This is where most of life in the ocean exists. Life can be microscopic, like the plankton that use the plentiful sunlight for photosynthesis. This is additionally where most marine mammals live.

Mesopelagic Zone:

The mesopelagic zone is also known as the twilight zone occurring 200 - 1,000 meters deep. Here there is faint sunlight, but no photosynthesis and becomes very dark as depth increases. Animals that produce bioluminescence or light inhabit the deeper waters of this sub-zone. Moreover, nutrients here are limited; some animals rise to the epipelagic zone at night for food. As well, many creatures can eat ones larger than themselves due to their large sharp teeth and expandable stomachs and jaws. The bigscale fish with oversized scales and bony plated head inhabits these waters. Similarly, other fish in this region rely on specially developed lures to catch prey off guard and to save energy in this nutrient-poor environment. Another organism living in this sub-zone is the ctenophore is a relative of the jellyfish and is also a bioluminescent organism and has adapted its iridescent cilia, used for locomotion, to scare away its predators2.

Bathypelagic Zone:

The bathypelagic is 1,000 - 4,000 meters down3. Animals living in the bathypelagic zone depend on detritus for food or eating other animals. At this depth and pressure, the most common animals found are fish, mollusks, crustaceans, and jellyfish. Additionally, sperm whales hunt at these depths to prey on giant squids. Black and red are commonly the colours of creatures here, and bioluminescence tends to be blue because red is not visible at these depths. The most common mollusk here is the vampire squid, an animal that can turn itself inside-out to use its spiky tentacles to deter predators or capture prey. Shrimp, amphipods (crustaceans) and scavengers are situated in the bathypelagic zone hide using a transparent red body. Furthermore, anglerfish are also found here, well known for their enormous mouth and a lure on its head. Not only does the anglerfish have enormous long teeth, and are also equipped with teeth in its throat. Male anglerfish are found in the form of a tiny parasitic fish carried by the female near her genitals₂.

Abyssopelagic Zone:

There are only a few organisms have adapted to survive in the abyssopelagic zone, 4,000 meters below the surface with freezing temperatures and incredible pressures. Deeper than the abyssopelagic zone is the hadapelagic zone where there are canyons and submarine trenches, below 6,000 meters to about 11,000 meters₂. Species capable of living at these depths include some species of squid, such as the deep-water squid, and octopus₄. As an adaptation to the aphotic environment, the deep-sea squid is transparent and also uses bioluminescence to lure prey and deter predators.

Physical Characteristics of Deep Sea Creatures

The physical characteristics of the deep ocean have led to fascinating adaptions of deep sea life for sensing, feeding, reproducing, moving, and avoiding being eaten by predators. Abiotic factors are lack of light, pressure, currents, temperature, oxygen, nutrients and other chemicals. Biotic factors include other organisms that may be potential predators, food, mates, competitors or symbionts.

Light:

The deep sea begins below about 200 meters, where sunlight becomes inadequate for photosynthesis to occur. There is a faint light in the mesopelagic zones, but sunlight continues to decrease until it is completely gone. This soft light is dark blue in colour because all the other colours of light are absorbed in depth. The deepest ocean waters below 1,000 m are entirely black₃. An adaptation species of the deep have formed is bioluminescence; a chemical reaction in a microbe or animal body that creates light without heat₂. Although this light is not sufficient in comparison to sunlight, so organisms living here need additional special sensory adaptations. Many deep-sea fish such as the stout blacksmelt have very large eyes to capture what little light exists and also to catch prey and avoiding predators. Lanternfish have the ability to focus and channel in whatever little light they get. Lastly, tripodfish, are essentially blind and instead rely on other, enhanced senses including smell, touch and vibration. There are six different functions that bioluminescence serves:

1.      Forward-facing light organs called photophores like those of the lantern fish;

2.      Social signals such as unique light patterns for attracting mates;

3.      Lures to attract curious prey, such as the dangling "fishing lures" of anglerfish;

4.      Counterillumination; rows of photophores on the bellies of many mesopelagic fish produce blue light matching the faint sunlight from above making the fish invisible to predators below them;

5.      Confusing predators or prey, for example, the bright flashes that some squid make to stun their prey, and decoys that divert attention, such as the glowing green blobs ejected by green bomber worms;

6.      The illumination of attacking predators and some swimming sea cucumbers even coat their attackers with sticky glowing mucus so that others can find them many minutes later.

Most bioluminescence is blue, or blue-green, because those are the colors that travel farthest through water. As a result, most animals have lost the ability to see the red light, since that is the colour of sunlight, which disappears first with increased depth. However, a few creatures, like the dragonfish, have evolved the ability to produce red light. This light, which the dragonfish can see, which they use to shine on prey so that the prey does not know it is luminated3.

Pressure:

Hydrostatic pressure is one of the most significant environmental factors affecting deep sea life. Pressure increases 1 atmosphere (atm) for each 10 meters in depth; the deep sea varies in depth from 200 meters to about 11,000 meters, therefore, pressure ranges from 20 atm to 1,100 atm plus. Fish have swim bladders, an internal gas-filled organ that contributes to the ability of a fish to control its buoyancy, high pressures cause air pockets, such as these to be crushed. However, it does not compress water very much instead it distorts complex biomolecules, particularly membranes and proteins needed for life. There are two ways that pressure effects biomolecules:

1.      Membranes and proteins have pressure-resistant structures that the work by mechanisms not yet completely understood, but this also causes the biomolecules not to function well under low pressure in shallow waters.

2.      Some organisms may use piezolytes, an organic molecule, found in organisms in shallow and deep water where it encounters hydrostatic pressure and osmotic pressure₅, the purpose is to prevent pressure from distorting large biomolecules. Trimethylamine oxide (TMAO)  is a piezolyte, most recognizable due to the fishy smell of marine fish and shrimp it causes. TMAO levels increase linearly with depth and pressure in other species.

Pressure-adapted microbes have been retrieved from trenches down to 11,000 meters and have been found to adaptations such as pressure-resistant biomolecules and piezolytes. However, pressure adaptations have only been studied in animals down to about 5,000 meters. It is unknown if these adaptations work at greater depths, down to 11,000 meters deep₃.

Temperature:

The difference in temperature between the euphotic zone near the surface and the deep sea can be dramatic. Thermoclines and the separation of water layers cause differing temperatures. A layer of warm water over 20°C floats on top of the cold, dense deeper water. In most parts of the deep sea, the water temperature is more uniform and constant remaining between about -1 to +4°C. However, water never freezes in the deep sea because of salt, seawater freezes at -1.8°C. Life in the deep sea is thought to adapt to this intense cold with flexible proteins and unsaturated membranes that do not stiffen up in the cold; membranes are made of fats and are somewhat flexible to work well. The downside of this adaptation is that loose membranes and proteins of cold-adapted organisms easily fall apart.

Oxygen:

The dark, intensely cold waters of the deep sea have a sufficient amount of oxygen. There is oxygen because cold water can dissolve more oxygen than warm water, and the deepest waters originate from shallow polar seas. In particular places in the northern and southern seas, oxygen-rich waters cool off then becomes dense causing it to sink to the bottom of the sea. These thermohaline currents can travel at depth around the globe, and oxygen remains sufficient for the surrounding life because there is not enough biomass to consume all of it. However, there are also oxygen-poor environments where there is no oxygen made by photosynthesis or thermohaline currents. These areas, called oxygen minimum zones; found at depths between 500 - 1,000 meters₃. Animals and bacteria in these areas feed on decaying food particles to get enough oxygen.

Food:

Deep sea creatures have evolved some unique and fascinating feeding mechanisms because food is extremely scarce at such depths. Since there is no photosynthesis this deep, most food consists of detritus; the decaying remains of microbes, algae, plants and animals from the upper zones of the ocean and other organisms from the deep. On occasion corpses of large animals, such as whales, sink to the bottom providing rare, but enormous feasts for deep sea animals; including, jawless fish such as hagfish, which burrow into carcasses, quickly consuming food outwards. Similarly, deep-sea pelagic fish such as gulper eels have gigantic mouths, huge hinged jaws and huge expandable stomachs to engulf large amounts of scarce food. Many deep-sea pelagic fish have extremely long fang-like teeth that point inward to ensures that any prey captured has little chance of escape. Species such as deep sea anglerfish and viperfish are equipped with a long, thin dorsal fin tipped with a photophore used to lure prey. Fish such as these do not use much energy while swimming in search of food because these species remain in one place and ambush their prey using clever adaptations such as these lures. Likewise, rattails and grenadiers cruise slowly over the sea floor using heightened senses to listen and smell for food sources falling from above. Another adaptation to save energy is by having watery, gelatinous tissues with low nutrient content.

Some mesopelagic species have adapted to the low food supply with a special behavior called vertical migration. At dusk, millions of lantern fish, shrimp, jellyfish and an abundance of other mobile animals migrate to the surface waters to feed in the darkness of night because it is rich with food₃. To avoid being eaten in daylight, they return to the depths after to digest. Some of the species undergo tremendous pressure and temperature changes during their daily migrations, but it is not yet know exactly how they cope with those dramatic daily changes. Another adaptation deep sea organisms have formed is the ability to go weeks without food. Also as soon as deep sea creatures have eaten something, it takes a long time to digest its meal so that the food supply can last longer. Since plankton are scarce in the deep sea, filter feeding is difficult to live off of. Consequently, some deep sea animals belonging to groups that were assumed to be only filter feeders have evolved into carnivores. For example, the carnivorous sea squirt Megalodicopia hians; sea squirts are usually harmless filter feeders which draw in microscopic organisms through a siphon tube, but Megalodicopia hians has an enormous jaw-like siphon that can rapidly engulf swimming animals. Another species like this is the tree sponge, Chondrocladia lampadiglobus. Sponges draw in microscopic material through tiny pores, but this sponge has tree-like branches with large globes covered in sharp spikes that impale swimming prey.

Adaptations

Body Colour:

Body colour is most often used by animals to camouflage and protect creatures from predators. In the deep sea, species bodies tend to be transparent (such as many jellies and squids), black (such as blacksmelt fish), or even red (such as many shrimp and other squids). The absences of red light at these depths keep them concealed from both predators and prey. Additionally, hatchetfish have silvery sides that reflect the faint sunlight, making them hard to see.

Hatchet fish 

Reproduction:

It is extremely hard to find a mate at such deep dark depths. It is unknown how most sea species achieve reproduction here. The deep sea anglerfish uses light patterns and scents to find mates, but they also have another interesting reproductive adaptation. Males are tiny in comparison and attach to the females using hooked teeth, establishing a parasitic-like relationship for life. The blood vessels of the male merge with the female so that he can receive nourishment. In exchange, the female anglerfish is provided with a large amount of sperm, avoiding the problem of having to locate a new mate every breeding cycle.

Gigantism:

Another possible adaptation that is not fully understood is called deep-sea gigantism. Gigantism is when certain types of animals to become enormous in size. For example the giant squid, there are also many others such as the colossal squid, the giant isopod, and the recently captured giant amphipod. It is not known how such animasl achieve such growth

Long Lifespans:

Many deep sea organisms have been found to live for decades and even centuries. Grenadiers, for example, may live to 56 years or more. Species in the deep sea reproduce and grow to maturity very slowly, so populations take decades to recover.

Hydrothermal Vents

A hydrothermal vent is the result of seawater percolating down through fissures in the oceans crust where geothermally heated water comes out of. Hot magma and re-emerges heat the cold seawater. Seawater in hydrothermal vents may reach temperatures of over 350°C5. These vents were surrounded by large numbers of organisms, with not only high densities of numerous new species, but also a new kind of ecosystem flourishing.These ecosystems are dependent on the chemical processes that results from the interaction of seawater and hot magma associated with underwater volcanoes.  The most phenomenal species found was a Riftia giant tubeworm; these grow rapidly in dense clusters, and these 2-meter-tall worms have no digestive tract. These worms live off of energy-rich hydrogen sulfide from the vent water generated in the Earth's crust. Hydrogen sulfide is normally toxic to animals, but these worms avoid with a bacteria known as chemoautotrophs in a large sac replacing a digestive system. These worms can use the energy in hydrogen sulfide to convert carbon dioxide into sugars. Other animals with bacterial symbionts have been found, including other species of tubeworms, giant clams and mussels, snails, and shrimp. These ecosystems are found to run on the Earth's geothermal energy rather than sunlight. Many scientists now think that life on Earth began at such vents over 3 billion years ago3.

Cold Seeps

Other unexpected high-density deep-sea ecosystems were found such as cold seeps. Cold seeps are areas of the ocean floor where hydrogen sulfide, methane, and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool6. Cold seeps occur at places where cold methane, hydrogen sulfide, and oil seep out of sediments providing plentiful amounts of energy.  Organisms with symbiotic bacteria related to other vent species were found in cold seep this includes; tubeworms, clams, and mussels. These ecosystems are powered by natural gas demonstrated sulfide-using bacteria instead of using methane. Dense seep communities around brine pools; salt deposits under the ocean floor dissolve to form pools of water so dense from their salt content that they do not mix with the seawater. High densities of mussels live around the rim, using symbionts on methane gas seeping from the pool. However, no known animal can survive the salt within the pool.

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