Exploring Extreme Ocean Zones: Life in the Abyss

1.0 Intro

What is an extreme environment?

A severe environment is an environment where humans might not live without technological support. Organisms that reside in these environments possess special adjustments that allow them to make it through the extreme conditions of their environment.1 A severe environment can be defined by conditions that are far outside the borders in which people dwell easily, in these categories: pH levels, pressure, temperature level, salinity, radiation, desiccation, and oxygen level. An organism that thrives in an extreme environment is called an extremophile.

A severe environment is one that does not fulfill the standard needs of human life.

2.0 The ocean zones

The ocean has 5 different zones as the depth increases, the epipelagic, mesopelagic, bathypelagic, abyssopelagic and lastly the haedoplagic zone. These zones 2extend from the surface to the most severe depths where light can no longer penetrate. These deep zones are where some of the most unusual and fascinating animals in the sea can be discovered. As we dive deeper into these mostly unexplored locations, the temperature drops and the pressure increases at an astonishing rate.

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The following diagram lists each of these zones in order of depth. Animals residing in different zones will have various adaptations to help them make it through the conditions in their zone. [pic]
http://www.eoearth.org/article/Bathypelagic_zone?topic=49523

2.1 The Epipelagic zone

The Epipelagic zone is the zone closest to the surface area. Life is abundant here, with all ranges of fish, mammal and shellfish living together.3 90% of all ocean life resides in this zone since of warm temperature levels and sunlight that goes down about 200 metres.

This is the only zone to support plant life because it has the light required for photosynthesis, which is very important due to the fact that it produces a lot of oxygen and some carbon. Due to the fact that of the range in plant life there is a range of animals including sharks, mackerels, tuna, seals, jellyfish, sea lions, sea turtles, sting rays, and far more! Though there are a lot of plants, there aren't extremely numerous places to conceal. For that reason some types have developed a camouflage called counter shading. Counter shading is when an organism is dark on the top of their bodies, and light on the bottom. This helps disguise them so that if a predator is looking up at them they will blend in with the water above and if they are looking down at them they will blend in with the darker water below.

2.2 The Mesopelagic Zone

The Mesopelagic zone extends from 200 to 1000 metres. Many animals living in the mesopelagic zone possess swim bladders full of gas that help them to migrate to the epipelagic zone to feed at night. These also help the organism to cope with the change in pressure, and to hide from large predators in the mesopelagic zones dark oxygen depleted waters. These species 4 usually have well-developed muscles and bones, and are usually somewhat streamlined. By contrast, fish that remain as ‘sit and wait’ predators in the mesopelagic zone lack a swim bladder, and have flabby muscles and watery flesh, or actively attract prey with bioluminescent lures. Bathypelagic organisms are mostly black, red or transparent, rendering them essentially invisible in the weak biological light. Because they do not go anywhere, streamlining has either not evolved or has disappeared.

2.3 The Bathypelagic Zone

In the bathypelagic zone, most organisms 4 are unable to undertake vertical daily migrations because below a certain depth the pressure is too great and the swim bladder is unable to function – gas cannot be produced. Most of these fish lack swim bladders or, like orange roughy, have bladders that are filled with wax. Sharks do not have swim bladders but are able to move vertically. To plane up and down they rely on strong swimming and the buoyancy provided by their oily livers (oil is less dense than water). This zone is located at a depth of 1000 to 4000 metres. The only source of light is from bioluminescence, as no sunlight can reach these depths. The pressure is enormous; at 5800 psi (pounds per square inch) it is almost 400 times the pressure at sea level (14.7 psi).

2.4 The abyssopelagic zone

This zone extends from 4000 to 6000 metres deep. 5The water temperature is so cold that it is near freezing, and there is no light at all. Very few creatures can be found in these freezing, no light, and bone crushing depths. Most of these creatures are invertebrates, such as basket stars and tiny squids. This zone has about three fourths of the ocean floor in it, and the pressure is up to 11,000 psi which is 750 times the pressure at sea level. Many abyssal creatures have under slung jaws to sift through the sand to catch food. Because food is very scarce, organisms often have the capacity to ingest large quantities of food at once, for instance the gulper eel has an elasticised stomach so it can eat things bigger than itself.

The haedopelagic zone

The haedopelagic zone is all the water that is in the ocean trenches. Not many organisms live in this zone because there is very little food and oxygen. 6Most life at this depth is sustained by marine snow or the chemical reactions around thermal vents. The intense pressure and the lack of light create hostile living conditions and few species are adapted to exist here. As no sunlight reaches this layer of the ocean, deep sea creatures have adapted with reduced eyesight, having very large eyes for receiving only bioluminescent flashes. Most of the bottom-dwelling creatures lack any pigmentation, since coloration is not useful in an environment with no light. Organisms from this zone will die in the zones where pressure is lower. The most common organisms include jellyfish, viperfish, tube worms and sea cucumbers. The haedopelagic zone can reach far below 6,000 meters deep, and at such depths the pressure in this zone exceeds 16,000 psi.

3.0 The Bathypterois

The bathypterois is a genus of deep sea tripod fish. The name comes from the Greek word bathys which means ‘deep’, and pterois which means ‘with wings’. There are currently 19 species of this genus, and the most well-known of these is the bathypterois grallator, or common tripod fish. Below is a list of the 19 species.

3.1 Adaptations Bathypterois have elongated pectoral and pelvic fins. In the case of the tripod fish, B. grallator, these fins are up to a metre in length, and are used for standing on the sea floor. Some species of bathypterois are capable of splaying the elongate pelvic and anal fins allowing them to rest, tripod-like on the bottom, with the body raised above the soft mud. The elongate pectoral fins have an 'elaborate nerve supply'. These fins are held up and out to the side of the body and are used to detect water movement and to trap and direct towards the mouth the small crustaceans on which it feeds. 7 It is thought that the eyes of bathypterois are reduced because of the general lack of light at the great depths where these fishes live. They have either very small eyes or enlarged eyes that lack any lens.

3.11 Feeding The B. grallator’s ventral fins and tail each have one elongated ray on which the fish perches, elevating it over the floor of the ocean.8The pectoral fins are held high over the head, curved so that is enlarged, extra-sensitive nerves can detect nearby motion, perhaps of the plankton on which the fish feeds. It is unclear exactly how the fish feeds on this plankton, however; although the fish does face into the current when resting on its "tripod" of fins, no one has seen the fish with its mouth open while in this position.

3.12 Reproduction

Some Bathypterois, including the B. grallator are hermaphroditic and may be able to self-fertilize in the event that another fish is not nearby, making reproduction easier a for the species, being greatly spread out in a vast environment.

3.13 Sensory Organs Having reduced sight, bathypterois need to find other ways to sense their environment. Fish usually have these hair-bearing sensory cells along their lateral lines, giving them a sixth sense of nearby motion. The bathypterois, however, has these cells all over the head and body, and they are directly exposed to the open water rather than contained in mucus-filled canals. The bathypterois is therefore even more sensitive than most fish to the motion of nearby possible predators, such as other fish. This trait is common to the nineteen species of bathypteroids to be found in the ocean, many of which do not have eyes at all, but rather flat sensory lobes similar to the eyespots of some vent shrimp. The main difference between each species is the length and arrangement of the pectoral fin spines. The different kinds of fish can also be found at different levels of the ocean, with B. longipes found at the lowest depths. The tripod fish is the most commonly-photographed member of the genus and is found in many places, including sometimes near hydrothermal vents or cold seeps.

3.14 Size

Compared to shallow water fish, the bathypteroids are relatively small. They range from between 14 and 45 cm long, compared with shallow water fish size, which can be up to 20m. Their small size means they don’t need as much food as a bigger fish would, and with the limited food at those depths, this is an important adaptation for survival at these depths.

3.15 Ontogenetic vertical migration

Ontogenetic vertical migration is when the juvenile organism hatches in shallow waters and migrates to deeper waters as it matures. Many species of the bathypterois undertake ontogenetic migrations during their lifetimes. The eggs hatch in fertile, warm waters, with plentiful food and shelter. Because larval bathypteroids are small, transparent and difficult to see, they are relatively safe from predators, but as they grow, they must go deeper to seek refuge from predators, but they are now more capable of looking after themselves in the harsher conditions. Not much is known about the mid stages of the bathypteroids, but they must undertake huge physical changes to cope with the extreme change of environment and pressure.

3.2 Habitat, locations and sightings

Bathypteroids occur in continental slope and abyssal waters of all oceans. They are some of the world's deepest living fishes, living at depths ranging from around 1000 m to over 6000 m. They occur in areas where the seabed is made up of ooze or very fine sand. Larvae are sometimes encountered in shallow water.

It is a common strategy for the8 larvae of the bathypteroids to live in surface waters and descend to the depths as they mature. This is known as an ontogenetic vertical migration. This allows them to feed in comparatively prey-rich waters. The image shows just such a larva, of the genus Bathypterois photographed at a depth of 5 m by Dan Dickinson on a night dive.