HADAL ZONE: CHARACTERISTICS, FLORA AND FAUNA - ENVIRONMENT - 2025

The hadal zone, hades zone or ultra-abyssal zone is the deepest oceanic area, located below 6 thousand meters of depth. It corresponds to topographic features on 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.

Bathymetric areas. Taken and edited from: TomCatX, Finlay McWalter, DieBuche. Polish version: Szczureq, via Wikimedia Commons.

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.

Bathymetric zones of the oceans

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 the 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:

According to the background

Neritic: 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.

According to the water column

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

Abisopelagic: 4001 to 6000 m depth

Hadalpelagic: 6001 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.

characteristics

The hadal zone is located 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, lack of light, and other factors severely limit biota. However, there is life capable of thriving at more than 1000 atmospheres of pressure and that particularly characterizes this area of ​​the ocean.

Deeper fairy zones

Ordered from least to greatest depth, the following graves are found:

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.

Flora

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.

The vegetal remains come from the surface or from photic areas of the water column and they arrive there after being removed by storms or hurricanes, for example.

Fauna

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 various invertebrate phyla and different families of vertebrates.

Invertebrates

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 organisms of the phyla:

-Porifera, with at least one kind 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 20,000 to 80,000 individuals per square meter.

-Mollusca, with about 40 species of snails, 47 of bivalves, and in a much smaller number of species, the 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 quite 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.

Giant amphipod Alicella gigantea. Illustration. Taken and edited from: Édouard Chevreux (1846–1931), via Wikimedia Commons.

Vertebrates

Among vertebrates, fish are the ones that dominate the hadal zone, as it happens 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 out Pseudoliparis amblystomopsis, a species of slimy fish of the Liparidae family described in 1955.

Slimy fish from the hadal zone Pseudoliparis swirei. Taken and edited from Gerringer ME, Linley TD, Jamieson AJ, Goetze E., Drazen JC, via Wikimedia Commons.

References

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4. Oceanic fossa. EcuRed. Recovered from ecured.cu.
5. M. Monks. Animals & Plants in the Hadal Zone. Recovered from sciencing.com.
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7. Hadal area. Recovered from ipfs.io.