The hadal zone, hades zone or ultra-abyssal zone is the deepest oceanic area, located below 6 thousand meters deep. Corresponds to topographic features of the ocean floor, such as ocean trenches (also known as ocean trenches).
It is characterized not only by its bathymetry (depth), but also by the biotic and abiotic factors that prevail. Due to its depth, it is a very little studied portion of the ocean..
Man's first mission to the hadal zone is relatively recent (1950). For its exploration, special equipment is required to withstand the high pressures that exist in that area..
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Scientists have divided the ocean in many ways. Depending on the science you apply, the ocean can be divided by its biota, by its depth or by its geological condition. The division into bathymetric zones correspond to oceanography.
Oceanography is the science that studies physical and chemical processes, currents, tides, and the structure and dynamics of the ocean, seas, and coasts. Marine bathymetry is responsible for studying the depths of these bodies of water. The sea depths are classified as:
Neritics: 0 to 200 m deep
Bathyals: 201 to 4,000 m deep
Abyssal: 4,001 to 6,000 m deep
Hadales: 6,001 to more than 10,000 m depth.
Pelagic - Epipelagic: from the water surface (0 meters deep) to 200 m deep.
Mesopelagic: 201 to 1,000 m deep.
Bathypelagic: 1001 to 4000 m depth
Abyssopelagic: 4001 to 6000 m depth
Hadalpelagic: 6001 up to more than 10,000 m deep.
These areas are currently the most recognized and used in the scientific literature. However, like everything in science, these classifications are always under constant review..
The hadal zone is below the abyssal zone, more than 6 thousand meters deep. This area represents approximately 1.9% of the area of the oceans. It is known for having very low temperatures (compared to other bathymetric areas).
There is no penetration of sunlight. It has a high hydrostatic pressure, it is a very poor area in nutrients. It is considered very still or static waters.
Nutrient poverty, the absence of light and other factors considerably limit the biota. However, there is life capable of thriving at more than 1000 atmospheres of pressure and that particularly characterizes this area of the ocean..
Ordered from least to greatest depth, are the following graves:
Kermadec, Pacific Ocean, near New Zealand: 10,047 m deep.
From the Kuriles, Pacific Ocean, Russia: 10,542 m deep.
Philippines, Pacific Ocean: 10,545 m deep.
Tonga or Tonga-Kermadec Trench, Pacific Ocean, near New Zealand and the Kermadec Islands: 10,882 m deep.
Marianas, Pacific Ocean, near Guam and the Mariana Islands: Depth 11,034 m.
The total absence of light prevents plants from thriving in these extreme places. Due to this, the presence of plants, multicellular algae and microalgae is almost totally ruled out..
Primary productivity in this zone is dominated by bacteria. Although the presence of flora in the hadal zone is not known, it is known that the fauna present there is adapted to feeding on plant remains such as seagrass meadows, terrestrial plants and microalgae.
Vegetable remains come from the surface or photic areas of the water column and arrive there after being removed by storms or hurricanes, for example.
In general, it has been shown that the diversity of marine fauna is inversely proportional to depth. Deeper, fewer species.
The species that live in this area have undergone various modifications such as adaptations to particular environmental conditions. Despite the inhospitable nature of the area, there are species of several invertebrate phyla and different families of vertebrates..
Invertebrate is not a term with taxonomic validity. This term, however, is widely used by scientists to group all those animals that are not within the subphylum Vertebrata (animals with backbones).
Multiple investigations indicate that the hadal zone is represented by phyla organisms:
-Porifera, with at least one species of marine sponge.
-Nematoda, considered a highly diverse and successful group in these environments. It has more than 190 hadal species. Their populations can be from 20 thousand to 80 thousand individuals per square meter.
-Mollusca, with about 40 species of snails, 47 of bivalves, and in a much smaller number of species, dandelions (scaphopods), chitons and monoplacophores.
-Echinodermata, represented by about 53 species of sea cucumbers, 25 species of sea spiders or brittle stars, 17 species of stars, and at least 10 species of sea urchins.
-Subphylum Crustacea, a group represented by more than 261 species. These include small crustaceans such as skeleton shrimps, isopods and amphipods..
Among the amphipods there is a rather peculiar species called Alicella gigantea, which can measure more than 30 centimeters, a fairly large size compared to the rest of the amphipods, which measure only a few millimeters.
Some species of cnidarians (anemones and jellyfish), polychaetes (wandering worms) and other invertebrate organisms have also been reported..
Among vertebrates, fish dominate the hadal zone, as in other areas of the ocean. The approximate number of species in this zone is confusing, since some authors do not differentiate between the organisms of the abyssal zone and those of the hadal zone..
Recent data indicates that there are about 15 species of fish that live more than 6 thousand meters deep. Among these, we can point to Pseudoliparis amblystomopsis, a species of slimy fish in the Liparidae family described in 1955.
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