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"Cold spring of hippocampus" breeds deep-sea "oasis"
Xiao Xi Tao Jun Liang Qianyong

In the distant South China Sea of China, people accidentally discovered an "oasis"-"cold spring of hippocampus" biological community in the deep sea. In the dark depths of the deep sea, the "cold spring of hippocampus" provides shelter for a variety of benthic organisms and nourishes a huge oasis life.

"Hippocampal Cold Spring" A giant active cold spring on the seabed found in the Pearl River Mouth Basin

Cold spring is another important discovery after submarine hydrothermal solution. Below the seabed sedimentary interface, fluids such as methane, hydrogen sulfide or hydrocarbons overflow from the seabed in the form of gushing or leakage, forming a submarine cold spring activity.

Plume flows are found in different marine sediment environments in major sea areas around the world. At present, tens of thousands of cold spring leakage points have been found according to multi-beam water data, and there are at least 100 active methane leakage areas, which are mainly distributed on the continental margin. It is estimated that the total amount of methane leaking from the submarine cold spring to the ocean every year can reach 400,000 ~12.2 million tons, which is one of the important natural sources of methane in the atmosphere. In addition, gas hydrate with shallow burial and high saturation often develops near the cold spring, which is an important window to study the mechanism of methane leakage and migration after gas hydrate decomposition. Therefore, it is of great scientific significance to carry out cold spring investigation and research.

In China, there are mainly seven cold spring areas in the offshore, among which Okinawa Trough 1 cold spring area is found in the East China Sea, and the other six cold springs are all distributed in the South China Sea. On March 20 15, Guangzhou Marine Geological Survey of China Geological Survey (hereinafter referred to as "Guanghai Bureau") discovered a huge active cold spring on the seabed in the Pearl River Mouth Basin for the first time by using the 4,500m unmanned submersible (ROV) independently developed by China, and named it "Haima Cold Spring". In the following years, Guanghai Bureau continuously upgraded the technical equipment of "Haima" ROV, organized many large-scale "Haima Cold Spring" surveys to enjoy the voyage, and the major marine universities and scientific research institutions in the United Nations comprehensively used a variety of high-precision survey equipment to carry out the cold spring investigation and research on a systematic scale.

Based on the breakthrough of multi-platform technology, the "Haima" opened the door to a new world of "Haima Cold Spring" for us, and the colorful cold spring biological community made a magnificent appearance ...

Primary producer chemical energy self-maintenance product

Anaerobic archaea and sulfate-reducing bacteria in seawater actively participate in the chemical reaction of methane oxidation and sulfate reduction in cold spring fluid, which provides carbon source and energy for chemoautotrophic organisms.

When methane comes into contact with seawater with little dissolved oxygen, special bacteria will grow. These bacteria consume methane and sulfate in seawater and release hydrogen sulfide. Although hydrogen sulfide is toxic to most animals, chemoautotrophs can use this chemical as food, and finally supply the energy and carbon sources needed by heterotrophs. Therefore, these self-sustaining chemicals have become the primary producers of the cold spring ecosystem.

There are white or orange bacterial mats covering the seabed several centimeters to hundreds of meters in diameter in the "hippocampus cold spring" area. These bacteria are usually composed of large sulfur-oxidizing bacteria (one of chemoautotrophs). The adaptability of giant bacteria narrows the gap between oxygen supply and electron donors, so they often appear in cold springs with high total oxygen consumption and large methane overflow.

Primary consumers are benthic organisms such as mussels, clams and tubular worms.

Chemosynthetic bacteria and archaea form the bottom of the cold spring food chain, supporting a variety of benthic organisms, including deep-sea bivalves (clams, mussels, hats, etc.), worms (tubular worms and ice worms) polychaetes and other primary consumers.

Because chemosynthetic clams (scientific name "Companion Clam") can collect hydrogen sulfide by rooting sediments in their feet, they usually live in areas where methane leaks a lot in the "cold spring of hippocampus". Hydrogen sulfide overflows upward with methane fluid, and clams rely on sulfur-oxidizing bacteria for nutrition from gills. With a stable supply of hydrogen sulfide, these clams can live for a century, growing to more than15cm.

The deep-sea clams found in the "cold spring of hippocampus" can extend hundreds of meters away, which is particularly spectacular. Similarly, there are a large number of chemoautotrophic bacteria in the gills of the deep-sea clams. Usually, mussels only appear in the mouth of active cold springs, which is one of the earliest biological communities in the ecological succession cycle of cold springs.

As the longest-lived macrobenthos in the world, the longest tube worms found in the "cold spring of hippocampus" area can reach 1.6 meters. Usually, tubular worms only appear in the environment where the velocity of cold spring is low. In the late stage of cold spring development, when the velocity of cold spring decreases, tubular worms replace the original mussels as the main species. They have no mouth and digestive system, and live on nutrients produced by bacteria in their own tissues. These bacteria obtain sulfur ions from cold spring fluid and oxygen from seawater to synthesize organic substances necessary for the survival of tubular worms. Because tubular worms can extend their "roots" to the bedrock more than one meter, even if the hydrogen sulfide is completely exhausted on the surface but still exists underground, tubular worms can still live in groups.

Secondary consumers fish, crabs, starfish and other organisms.

In addition to mussels, clams, tubular worms and other symbolic biological communities of cold springs, "Haima Cold Spring" also gathers a variety of benthic organisms, such as eels, Alvin shrimp, armored shrimp, starfish, conch, sea snake tail and so on, which constitute the secondary consumers of the cold spring ecosystem.

Through the underwater camera function of the "Haima" ROV, researchers found a vibrant ecological scene in the "Haima Cold Spring" area: spider-like white crabs and huge king crabs were leisurely in the cold spring at the bottom of the sea, gulping down everything they could eat; Soft purple sea cucumbers shaped like earthworms are intertwined and distributed in groups to distinguish them from mussel communities; Tiny blind brown shrimps, scallops, armored shrimps, sea gills, sea snakes, fish, etc., gather in dense thin-tube insect jungles and hover up and down, forming a small ecosystem, which is very lively!

Third-level consumers: deep-sea carnivorous species such as octopus and king's foot.

Not only secondary consumers such as fish, crabs and starfish can be seen everywhere. Giant octopus was even found in the "hippocampus cold spring" area. The most surprising thing is that in the "Haima Cold Spring" at a depth of nearly 1400 meters, the "Haima" ROV successfully captured two "world's largest insects"-the king's podopod (commonly known as the deep-sea water louse), which was 25 cm long.

The deep-sea water otter is a typical deep-sea carnivorous species. Besides feeding on the carcasses of fish, crabs, shrimps, squid and whales, it also actively hunts some slow-moving marine creatures, such as sea cucumbers, sponges, nematodes, radiolaria and other benthic animals, and becomes the third-level consumer in the cold spring ecosystem. These large organisms will eventually be decomposed by microorganisms, thus returning to nature and forming a complete cold spring ecosystem.

(Author: Guangzhou Marine Geological Survey of China Geological Survey)