"Seahorse Cold Spring" Gives Birth to Deep Sea "Oasis"

　　Xiao Xi Tao Jun Liang Qianyong

　　In the distant South China Sea, people accidentally discovered an "oasis" in the deep sea - the "hippocampal cold spring" biome. In the depths of the pitch-black deep sea, the "Cold Spring of the Hippocampus" provides shelter for a rich variety of benthic creatures, nourishing vast oasis life.

　　"Hippocampal Cold Spring" Is a giant active cold spring found in the Pearl River Estuary Basin

　　Cold springs are another major discovery after hydrothermal fluids on the seabed. Under the sedimentary interface of the seafloor, fluids such as methane, hydrogen sulfide or hydrocarbons overflow from the seafloor in the form of gushing or leakage, forming a cold spring activity on the seabed.

　　Pinnate streams formed due to the leakage of seabed methane into seawater have been found in different marine subsoil environments in major seas around the world, and tens of thousands of cold spring leakage points have been found according to multi-beam water body data, and at least more than 100 active methane leakage areas are present, mainly distributed at the continental edge. It is estimated that the total amount of methane leakage from the cold springs on the seabed can reach 400,000 to 12.2 million tons per year, which is one of the important natural sources of methane in the atmosphere. In addition, shallow buried natural gas hydrates with high saturation often develop near cold springs, which is an important window for studying the mechanism of methane leakage and migration after decomposition of natural gas hydrates. Therefore, it is of great scientific significance to carry out cold spring investigation and research.

　　In China, there are 7 main offshore cold spring areas that have been preliminarily confirmed, one cold spring area has been found in the East China Sea, and the remaining 6 cold springs are distributed in the South China Sea. In March 2015, the Guangzhou Marine Geological Survey of the China Geological Survey (hereinafter referred to as the "Guanghai Bureau") used the 4500-meter -- "Haima" unmanned submersible (ROV) independently developed in China to discover the seabed giant active cold spring in the Pearl River Estuary Basin for the first time, and named it "Haima Cold Spring". In the following years, the Guanghai Bureau continuously upgraded the technical equipment of the "Haima" ROV, organized a number of large-scale "Haima Cold Spring" survey and sharing voyages, and the major marine universities and scientific research institutions in the United Nations comprehensively used a variety of high-precision survey equipment to systematically carry out cold spring investigation and research on a systematic scale.

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

　　Primary producers can be autotrophic organisms

　　Methane anaerobic oxidation archaea and sulfate reduction bacteria in seawater actively participate in the chemical reaction of methane oxidation and sulfate reduction in cold spring fluids, providing carbon sources and energy for chemical energy autotrophic organisms.

　　When methane comes into contact with seawater with little dissolved oxygen, special bacteria grow. These bacteria consume methane and sulfates from seawater and release hydrogen sulfide. Although hydrogen sulfide is toxic to most animals, auto-renewable organisms can use this chemical as food, ultimately supplying the energy and carbon sources needed by heterotrophic organisms. As a result, these auto-renewable organisms have become primary producers of cold spring ecosystems.

　　The "hippocampal cold spring" area presents white or orange bacterial pads covering the seafloor several centimeters to hundreds of meters in diameter, which are usually composed of large sulfur-oxidizing bacteria (one of the autotrophic organisms of chemical energy). The various adaptations exhibited by giant bacteria narrow the gap between oxygen supply and electron donors, so they often appear in cold springs with high total oxygen consumption and large amounts of methane spills.

　　Primary consumers Benthic organisms such as mussels, clams, tubular worms, etc

　　Chemical synthesis bacteria and archaea form the lowest layer of the cold spring food chain, feeding a variety of benthic organisms, including deep-sea bivalves (clams, mussels, cap shells, etc.), worms (tubular worms and ice worms) polychaetes and other primary consumers.

　　Because chemical energy synthesis clams (scientific name "conjunct clams") can collect hydrogen sulfide through filamentous deposits, they usually live in areas where "hippocampal cold springs" have a large leakage of methane. Hydrogen sulfide spills upward with the methane fluid, and clams rely on sulfur oxidizing bacteria from the gills for nutrients. With a steady supply of hydrogen sulfide, these clams can survive for a century and grow beyond 15 centimeters.

　　The deep-sea clams found in the "Seahorse Cold Spring" can extend hundreds of meters away, which is particularly spectacular. Similarly, the gills of the deep-sea clam contain a large number of autotrophic bacteria. Usually, mussels only appear at the mouth of active cold springs and are one of the earliest developed biomes in the ecological succession cycle of cold springs.

　　As the world's longest-lived macrobenth, tubular worms found in the "Hippocampal Cold Spring" area can reach up to 1.6 meters in length. Usually, tubular worms only appear in environments with low flow rates in cold springs, and in the late stages of cold spring development, when the flow rate of cold springs decreases, tubular worms replace the original mussels as the main species. They have no mouth and digestive system and depend on nutrients produced by bacteria in their own tissues. These bacteria obtain sulfur ions from cold spring fluids and oxygen from seawater to synthesize organic matter necessary for tubular worms to survive. Since tubular worms can extend their "roots" to more than a meter of bedrock, tubular worms can still live in groups even where hydrogen sulfide is completely depleted on the surface but remains underground.

　　Secondary consumers Fish, crabs, starfish and other creatures

　　In addition to the iconic biomes of cold springs such as mussels, clams, tubular worms, etc., "Seahorse Cold Springs" also gathers a rich variety of benthic organisms, such as eels, Alvin shrimp, armor shrimp, starfish, conch, sea snake tail and other organisms, constituting a secondary consumer of the cold spring ecosystem.

　　Through the "Seahorse" ROV seabed camera function, researchers found a vibrant ecological scene in the "Seahorse Cold Spring" area: spider-like white crabs, huge king crabs leisurely in the seabed cold spring, swallowing everything they can eat; soft purple sea cucumbers shaped like earthworms, entangled, distributed in groups, distinguished from mussel communities; tiny blind brown shrimp colonies, small scallops, armored shrimp, sea gills, sea snake tails, fish, etc. Clustered up and down in a dense jungle of thin tube worms, forming a small ecosystem, it is not bustling!

　　Tertiary consumers Deep-sea carnivorous species such as octopus and king footworm

　　Not only fish, crabs, starfish and other secondary consumers can be seen everywhere. Giant octopuses have even been spotted in the "Seahorse Cold Springs" area. The most surprising thing is that at the bottom of the "Seahorse Cold Spring" at a depth of nearly 1400 meters, the "Seahorse" ROV successfully captured two of the "world's largest insects" - the king pod (commonly known as deep sea lice) through the way of biological trapping cages, up to 25 centimeters long.

　　Deep-sea lice are typical deep-sea carnivorous species, feeding on fish, crabs, shrimp, squid and whale carcasses, but also actively hunting some slow-moving marine organisms, such as sea cucumbers, sponges, nematodes, radiolarians and other undersea animals, becoming the third level consumer in the cold spring ecosystem. These large organisms will eventually be decomposed by microorganisms, thus returning to nature, forming a complete cold spring ecosystem.

　　(Author Affilications:Guangzhou Marine Geological Survey, China Geological Survey)