In a previous article we explained the extreme conditions that exist in the great ocean depths , where sunlight is non-existent, dissolved oxygen in the water is scarce and the temperature is close to freezing. For all these reasons, life at great depths requires a series of specific adaptations to that environment and depends to a great extent on the contribution of organic matter from upper layers of water.
There are, however, some orchards of life at great depths that are almost independent of the upper world. In this article we explain what underwater vents are and what forms of life are found in these unique ecosystems.
What are underwater fumaroles?
The main contribution of food to the abyssal zone is the slow but constant descent of organic matter from upper water layers by means of marine snow. However, this is not the only food source available.
Hydrothermal water sources exist at great depths, which expel water at temperatures of up to 400 ° C. The immense pressure allows water to remain in a liquid state at these temperatures, well above its boiling point at atmospheric pressure.
Formation of underwater fumaroles
These sources are generated when sea water seeps through cracks in the bed, usually in the vicinity of an underwater volcano , where the magma is close to the sea bed. These leaks are facilitated by the enormous pressure of the water on the seabed, which can exceed 1,000 atmospheres in ocean trenches. Heat is transmitted through the rock and the water heats up rapidly, rising because it has a lower density than cold water.
High temperatures allow certain mineral compounds that are part of the seabed to dissolve in the water, so they are carried away by the rising current of hot water. The water is expelled and forms cylindrical structures by solidification of the dissolved minerals, which grow over time as matter accumulates, called fumaroles .
There are fumaroles that emit sulfurous compounds, the so-called black fumaroles , due to the color of the water they expel. There are also fumaroles that emit other types of compounds, the so-called white fumaroles . The fumaroles have a variable life time, some disappear and new ones are formed.
What organisms inhabit underwater vents?
Around the underwater fumaroles (also known as hydrothermal vents) a biological garden is formed, where microorganisms have adapted to produce energy and synthesize organic matter from the chemical compounds expelled by the fumaroles, from which they also take advantage of the heat that emit.
They are autotrophic, chemoautotrophic, or chemoautotrophic organisms . They differ from plants in that they obtain their energy from sunlight, so they are phototrophic autotrophic organisms, or photoautotrophs. Both types of organisms are primary producers and form the basis of food chains in ecosystems.
Thus, underwater fumaroles allow the existence of unique ecosystems at great depth. Crustaceans, mollusks or annelids are the most striking life forms in these ecosystems, reaching densities that in other parts of the abyssal zone would be unsustainable.
Perhaps the most representative form of life found around the fumaroles are the giant tube worms,  Riftia pachyptila , which grow to several meters in height and whose body is formed by a long whitish tube, from which a feather protrudes. red gill that the animal uses to breathe (whose color is due to the presence of hemoglobin).
Each of these worms has a symbiotic relationship with colonies of chemosynthetic bacteria, which live in the worm’s tissues and carry out the synthesis of organic molecules. This is the first known case of symbiosis between bacteria and a marine invertebrate . In addition, it is estimated that these worms are very long-lived, being able to live up to 250 years.
The fumaroles as the origin of life
It has been suggested that the first life forms on Earth could have arisen in ocean vents, due to the availability of resources and the energetically favorable environment.
Thus, in the environment near ocean vents, methane (CH 4 ) and ammonia (NH 3 ) are available, two molecules necessary for the formation of primitive life but which are not very abundant in environments where there is no previous life. Other molecules present in the thermal waters of the fumaroles, which have a certain catalytic capacity similar to that of enzymes, are methanol (CH 3 OH) and formic acid (HCO 2 H).Â
The life forms that are found around these underwater hydrothermal vents are not completely independent of the rest of ecosystems (although bacteria can be), because they require oxygen to survive. The oxygen present in seawater comes from the atmosphere, and its origin is the photosynthetic activity of plants and some microorganisms. Therefore, despite living in conditions of complete twilight, even the life of the animals of the abyssal zone is indirectly dependent on the Sun.Â
The survival of these ecosystems also depends on the existence of the fumaroles, so if these are exhausted, the ecosystem will die. There is a great unknown regarding these ecosystems, and it is how they have been able to establish themselves separately at different points on the seabed, with large distances between the different fumaroles, which do not allow the transit of the organisms that live in them. To this day, the issue remains unsolved.
Note: Underwater vents are also known as hydrothermal vents, hydrothermal vents, or underwater hydrothermal vents.
