Thriving In The Deep Sea; The Exciting Life of Giant Tube Worms
The Giant Tube Worm; Riftia pachyptila is an alien-like species standing at over 2 meters tall; with it’s red feathery surface, it’s specifically adapted to live in depths far exceeding a mile where there is no light at all. It lives in hydrothermal vent environments which are incredibly hot (often with water temperatures exceeding 400°C) and rich in toxic hydrogen sulphide, for this reason these environments are often considered some of the most extreme marine environments.
Riftia pachyptila. with their characteristic red bodies and white tubes are a common site in many hydrothermal vent environments (Image Credit; NOAA)
Hydrothermal Vents are located near volcanic activity, fissures in the sea floor allow magma to interact with sea water; this superheats the water causing it to drop any dissolved constituents in the form of a particle. The superheated water and the particles which were once dissolved then rise as the hot water is less dense than cold water creating a density gradient. This causes the water around hydrothermal vents to be very dangerous to unadapted animals; it has high concentrations of heavy metals, low concentrations of oxygen and is very hot.
A Hydrothermal Vent, the white smoke is due to the CO2 in the water when it was heated. The white smoke lead to this variety of hydrothermal vent being called a “white smoker” (Image Credit; wiki commons)
Riftia pachyptila are found as a part of often huge communities around black smokers; a specific type of hydrothermal vent, named after their huge black plumes of sulphide rich smoke.
Nutrition Around Hydrothermal Vents
If you’ve ever studied deep sea animals you’ll probably know most of them live very long lives and develop slowly, this is for good reason. Nutrients in the deep sea are very hard to come by; marine snow (particles organic material which fall from the surface to the deep sea), which is the primary source of food for many deep sea animals falls very slowly and therefore there is little available to sustain large communities unless they migrate towards the surface to feed.
Then how do communities of Riftia pachyptila exist? In order to survive in such a barren area animals around black smokers rely on the symbiotic bacteria Sulfurovum riftiae to convert the otherwise toxic hydrogen sulphide into usable nutrients, and as a result of this novel relationship Riftia pachyptila have no need for a mouth or a gut. They protrude their tentacles into the water and absorb as much of the toxic hydrogen sulphide as is possible, this is then transported through their blood like “haemolymph” to specialised cavities in which the Sulfurovum riftiae live called trophosomes. They in exchange for safety within the worm and food produce organic material in the form of ammonia for the worm to “eat”. In order to support a worm of the size of Riftia pachyptila a large amount of bacteria is required, therefore the animal has sufficient space to store more than double it’s weight in bacteria.
This allows large communities of animals to survive without any energy derived from the sun, an entirely new way of life when it was discovered in the 1980’s.
The bacteria Sulfurovum riftiae is essential to Riftia pachyptila as a result it may accumulate a large mass of the bacteria throughout it’s life; so much that it no longer requires feeding apparatus (Image credit; Rutgers)
How do They get Other Necessary Compounds?
As said earlier when the water is superheated it vastly reduces it’s ability to keep molecules dissolved in it, this is the same for important molecules such as nitrogen and oxygen, without which animals living near the vent site would be unable to survive, so how do they survive when the concentrations of these molecules are so low? They have evolved two forms of haemoglobin, although identical in structure they behave in two different ways. There is extracellular hemoglobin like in all animals which sits in designated vessels, this transports oxygen to cells throughout the body, however once within the cell oxygen binds to another molecule of hemoglobin that remains within the cell. This hemoglobin within the cell acts as a buffer, releasing oxygen when the concentration is too low and binding to oxygen when it is plentiful. Similar mechanisms in relatives of Riftia pachyptila allow them to survive up to 40 minutes without oxygen with no changes to any of their metabolic processes
Near vent sites life cycles are often strange, organisms need to have many offspring often as vents are short lived and once the vent ceases to expel it’s “chemical food” the organisms around it will often die. As a result of the quick lifestyle need to survive Riftia pachyptila can grow to 1.9 meters and reach sexual maturity in less than 2 years.
When reproducing females will release buoyant eggs rich in fats to aid development, this triggers the males to then release sperm packets which are highly motile to seek out the eggs and fertilize them. The young then quickly develop (the actual development time is unknown but as it can reach 1.9 meters in two years it is assumed to be short), after hatching the larvae swims around seeking out a place to settle based on the chemicals present and finally settles in a suitable place rapidly growing over the course of two years into a mature adult.
These fascinating creatures are about as alien as you could find on earth, utilizing an ecosystem that was unknown to science until recently making them completely different to anything most people would think signifies an animal.