Hydrothermal vents tend to be found in the deep sea on the tectonic plate boundaries that define our continents.  They are large segments of the earth’s crust which ‘float’ on top of the upper mantle, which is comprised of very hot molten magma that is around 500-900 degC. As these plates ‘float’ they tend to move and cause gaps in the earth’s crust. Water is able to move in between these gaps known as fissures, whilst in them the water is heated up by magma, where it is then forced back up to the sea bed creating a hydrothermal vent. Contrary to popular belief the deep sea is not flat, it is a very complex terrain which is rugged and full of ‘mountainous’ regions and deep trenches that are thousands of metres deep. The deep sea is also not a barren wasteland with no life, it is home to many undiscovered and unrecorded species which are constantly being discovered. the hydrothermal vents are no different, they are hotspots for marine life, all of which is uniquely different and adapted to these harsh environments. These creatures include species of shrimp, crabs, starfish, tubeworms and clams.

The process of how a hydro thermal vent is formed and how it functions
The process of how a hydro thermal vent is formed and how it functions to release hydrogen sulphide into the water (source)

Hydrothermal vents discharge a lot of toxic elements such as Carbon Dioxide (CO2) and Hydrogen Sulphide (H2S) through rapid cooling of the water and magma meeting through water vapour, which are fatal to most organisms both terrestrial (land) and marine (ocean). Though these hydrothermal vents are very toxic to life, there are thousands of organisms living around them, suggesting that there is a benefit to being adapted to living around these vents.

So why are hydrothermal vents such productive areas for marine life and how are these organisms able to live in such toxic conditions?

The reason organisms can live in these environments is due to a chemical process known as ‘chemosynthesis’ which produces a type of food for bacteria. This process is very similar to photosynthesis used in plants where the leaves convert the energy of the sun into energy used for the plants growth and development, except instead of using the energy from the sunlight the bacteria is using the energy from chemical reactions occurring in and around the hydrothermal vent. This is one of the very few ways life can sustain itself with zero light unlike the majority of the ocean relying on the transfer of phytoplankton energy being transferred through different consumers, or the complete dependency of the use of photosynthesis in the terrestrial environment, through the energy transfer of plant life through consumers.

Upon research of these deep sea marine creatures it has been discovered that the bacteria which converts the chemicals into food, are found inside some of the organisms that live by these hydrothermal vents. In the gill filaments that act as a filter during respiration, so when an organism intakes water the sulphide is taken up by the bacteria to be converted into food. Due to this the bivalves like the clam Calyptogena magnifica have much bigger gills than their shallow water cousins accounting for up to 20% of their body tissue, allowing for larger numbers of bacteria to live within them. The bacteria and animals have a symbiotic relationship (an equal relationship where both organisms benefit) when it comes to feeding and survival, as the bacteria targets well protected animals that are either burrowed or spend majority of their time under the seabed, as a form of protection from predators, in exchange they provide food for the host animal.

The bacteria are known as chemotrophic bacteria; it oxidises hydrogen sulphide (H2S), and is able to pull it from its host’s blood stream, giving it a constant supply of nutrition, and providing food back to its host. Examples of major predators include Galatheid Crab (Shinkaia crosnieri) also known a squat lobster, another is the Zoarcid fish such as the Pink Vent Fish (Thermarces Cerberus) which predate on the worms and mussels that the bacteria hold symbiosis relationships with.

Example of a food web found around a hydro thermal vent. It shows the lowest levels of the food web being bivalves, up to the tertiary predators the octopi.
Example of a food web found around a hydro thermal vent. It shows the lowest levels of the food web being bivalves, up to the tertiary predators the octopi. (source)

These organisms have also had to adapt physically to the high toxicity levels that are poisonous to them. Many polychaete worms create a mucus bubble that absorbs the toxins and then it is deposited on the seafloor. They have also adapted in a way known as gigantism where they are much larger than the shallow water versions, the tube worms go from a few inches in shallows to up to 8 feet long in the deep and have much more protective tubes that the live in, the giant bodies allow for much more bacteria to live within them and they don’t have mouths, anuses, intestines or stomachs, which demand a large energy supply, allowing the worms to focus energy on growth instead. Another organism that has adapted is the Scaly-Foot Gastropod (Crysomallon squamiferum) who’s shell is composed of iron sulphide released from the hydrothermal vents, that the snail binds to its shell. This shell protects it from predators but also stops the calcium carbonate shell found on all gastropods from dissolving in the acidic waters.

The scaly foot gastropod, where you can see the armour of iron sulphide that is used to protect itself from the acidic waters
The scaly foot gastropod, where you can see the armour of iron sulphide that is used to protect itself from the acidic waters (source)

The bacteria is the absolute keystone species in this habitat. Every single species relies on these bacteria to provide nutrients and energy in the food chain to be transferred up the levels of predation, especially in a habitat where there is no light, plant life/ algae and no photosynthesis. Therefore, no other producers are available, meaning there is no competition and all tertiary consumers (top of the food chain i.e. octopi) must rely on this relationship. However, it is a very efficient system as these organisms do not have to consume as much energy for feeding as it is happening inside of them. The organisms that have adapted to life at hydrothermal vents are the product of thousands of years of adaption and are some of the most successful and productive communities on the planet. The deep sea is one of the least studied areas we are unsure on how more creatures have adapted, continuing studies will help us understand more.

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