Three great deep sea oases found in the South China Sea

Three great deep sea oases found in the South China Sea

A few months ago, the “Deep Sea Warrior” carried out a deep-sea exploration in the South China Sea. Three systems of deep-sea oases such as whale falls, deep-sea hydrothermal vents, and cold seeps were found at a depth of 1,600 meters in the South China Sea. This is the first time that Chinese scientists have discovered such types of deep-sea ecosystems (Oases) in Chinese waters.


These deep-sea ecosystems are one of the largest reservoirs of biodiversity on the planet but remain one of the least studied ecosystems due to its remoteness and the technological challenges of its exploration.

Whale Fall

The images of whale falling taken by Chinese scientists in the South my country Sea, the picture comes from the co-chief scientist of TS16 voyage and associate professor Xie Wei, School of Marine Sciences, Sun Yat-sen University
The image of whale falling taken by Chinese scientists in the South China Sea

It is the first time that most natives have heard of this beautiful name-“Whale Fall”. Whale Fall refers to the carcass of a whale that has fallen into an ocean basin or abyss. Because scavengers cannot quickly decompose a huge body of cetaceans and other animals, they will fall to the bottom of the sea. The process of the corpse falling to the bottom of the sea can last from several months to several years and will provide food for all types of consumers in the food chain, including deep-sea fish, crustaceans, polychaetes, and various small creatures.

From the YouTube Channel-Nautilus Live
Whale fall ecological group (Picture from the YouTube Channel-Nautilus live)

In the end, the remaining skeleton will release hydrogen sulfide for the synthesis of autotrophic biochemical energy. This process can last for several years, and some anaerobic organisms can eat whale bones and break down lipids. The biological settlement formed by a whale fall can last for tens or even hundreds of years. In the deep ocean of the North Pacific, at least more than 10,000 organisms depend on the whale fall to survive.

The evolution of whale falls can divide into four stages:

1. Mobile scavenger stage (Mobile-scavenger stage)

When the whale carcass sinks to the bottom of the sea, creatures such as hagfish and sharks feed on the soft tissue in the whale carcass. Every day, these creatures plundered 40-60 kilograms of soft tissues, and the whole process lasts for several months, up to 1.5 years. This time, the whale falls discovered by Chinese scientists are still in the first stage, so it has long-term research value.

The whale landing in the Davidson Seamount in Monterey Bay
The whale falling in the Davidson Seamount in Monterey Bay (Picture from YouTube Channel-Nautilus live)

2. Opportunist stage (Enrichment opportunist stage)

Opportunists (some invertebrates, especially polychaetes and crustaceans) can adapt to the corresponding environment in a short time and reproduce quickly. These creatures thrive on the bones of whale carcasses and the surrounding strata as colonies. This stage can last up to 4.5 years.

The hairy biome in the whale colony
The hairy bio-me on the whale carcass (Picture from YouTube Channel-Nautilus live)

3.  Chemoautotrophic stage (Sulphophilic stage)

Sulfophilic bacteria enter the bones of whales and break down the lipids in the bones. Use sulfate dissolved in seawater as an oxidant to generate hydrogen sulfide. Chemoautotrophic bacteria such as Sulfobacteria use these hydrogen sulfide as a source of energy and use dissolved oxygen in water to oxidize it to obtain energy. Since whale bones are rich in lipids, which account for 4–6% of their body weight, the final digestion stage can last for 50 or even 100 years.

Evolve to the late whale fall
Final sate of whale falling (Picture from YouTube Channel-Nautilus live)

4. Reef stage

When the organic matter in the remnant whales is consumed, the mineral remains of the whale bones will be used as reefs and become habitats for creatures.

Hydrothermal Vent

The hydrothermal vent is also known as the Submarine Hydrothermal System, which ejects water heated by geothermal heat from the seabed and its cracks. It is usually found in areas where volcanic activity is frequent and continental plates are moving, near sea basins, and hot spots. Submarine chimneys are often formed on the seafloor.

Submarine hydrothermal fluid-black chimney
Submarine hydrothermal fluid-black chimney

Compared to other submarine areas at the same depth, life near submarine hot springs is usually more prosperous, and they rely on decomposing minerals from the hot springs for food.

Huge tubular worms gather around the vents of the Galapagos Rift Valley
Huge tubular worms gather around the vents of the Galapagos Rift Valley

It is generally believed that organisms must rely on sunlight for survival, but many deep-sea organisms can only rely on Haiti’s sediments for their livelihoods. Deep-sea hot springs provide shelter for these creatures, and the water near the seabed hot spring is rich in minerals and bacteria. Therefore, there are usually amphipods and copepods nearby. Larger creatures include fish, crustaceans, tube worms, and octopuses. The giant tubular worm can be up to 2.4 meters long and is one of the most important creatures near deep-sea hot springs.

They do not have a mouth and digestive tract and rely on the nutrients produced by bacteria in their own tissues. There are approximately 285 billion bacteria per ounce of tubeworm tissue. The red plume tissue of tubeworms contains hemoglobin. Hemoglobin binds to hydrogen sulfide and is transferred to bacteria living in tubular worms. The bacteria repay the tubeworm with nutrients containing carbon compounds. Other peculiar creatures living here are the scale-footed snails, whose very peculiar feet are attached with protective scales formed by iron compounds and organic materials.

Squamous snail (close-up)
Squamous snail (close-up view)

Cold Seep

Cold seep (cold seep), sometimes called cold spring vent, generally develops in the ocean floor area. The rich fluids such as hydrogen sulfide, methane and other hydrocarbons leak in the form of salt pools to form cold springs.

The salt pool in the cold spring in the deep-sea
The salt pool in the cold spring in the deep sea

“Cold” does not mean that the temperature of the cold spring is lower than the temperature of the surrounding seawater. In contrast, its temperature is generally slightly higher than the surroundings. The “coldness” of cold springs means that the higher temperature (at least 60°C) of the hot spring on the seabed is lower than the surrounding sea water. Such special chemical conditions have formed a unique rich biological community.

A large number of mussels distributed near the cold spring
A large number of mussels distributed near the cold spring

Cold springs are formed from seafloor cracks caused by geological tectonic activities. Oil and methane “leaked” out of these cracks. It is slowly spreading in the seafloor sediments, and forming large areas up to hundreds of meters wide. These chemicals provide unique conditions for the reproduction of thiophilic bacteria and other organisms.

Bacteria mat formed by the growth of a large number of bacteria, the red spot is laser ranging
Bacteria mat formed by the growth of a large number of bacteria, the red spot is laser ranger

With ecological succession, different biological communities grow symbiotically near the cold spring as the picture above.

Tube worms and mussels live in symbiosis near the cold spring
Tube worms and mussels live in symbiosis near the cold spring

Conclusion:

The marine ecosystem is far more complicated than we realize today. Whether it is a beautiful “whale fall” or a “hot spring” or a “cold spring”, it is only a tiny component of the marine ecology. With the deepening of our ocean research, more life oasis is waiting for us to explore!

A whale fall video from YouTube Channel-Nautilus live
Related stories :

https://aquaticmammal.blogspot.com/2020/04/whale-falling.html

https://www.chemistryworld.com/features/treasures-from-the-deep/3004870.article

More readings :

http://oceanfacts.net/diving-in-sri-lanka-and-southeast-asia/

http://oceanfacts.net/how-whales-play-a-crucial-role-in-assisting-the-function-of-the-earth/

References :
  1. Scientists Break Record by Finding Northernmost Hydrothermal Vent Field. Science Daily. 24 July 2008.
  2. Demise of Antarctic Ice Shelf Reveals New Life”. National Science Foundation. 2007. Retrieved 14 February 2008.
Photo and video source credit :

The videos and pictures in this article are taken by CGTN, Treasures from the deep, The Sea, Wikipedia, and You-Tube.

Rajitha Dissanayake

Researcher in the field of Marine Mammals and Bio-acoustic

I'm a Master’s student in marine mammals and bio-acoustic laboratory, Institute of Deep-Sea Science and Engineering (IDSSE), Chinese Academy of Sciences (CAS) and focusing on the sustainable environmental application, conservation, and exploring all aspects of the ecology and behavior of marine mammals.

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