Hydrothermal Vents: A World Beyond the Sun
The overwhelming majority of life on this planet relies on energy supplied by the sun, either directly through photosynthesis or indirectly via energy transfer from another organism within the food web of their particular habitat, but in 1977 off the coast of the Galapagos islands specifically at a site known as the Galapagos Rift at around 2,500 meters in depth, a new habitat was discovered by deep sea research vessel ‘Alvin’ these new environments were dubbed hydro-thermal vents and were absolutely teaming with new marine species that had never before been seen, but how are these environments formed? how have the organisms that live there adapted to the “extreme” environment in which they inhabit? what potential secrets or resources do these habitats hold?
Formation of Hydro-thermal Vents:
Hydro-thermal vents are created through the movement of the planets tectonic plate boundaries and occur along fault lines and fractures in the earths crust. They are created by the crustal plates moving away from each other or towards each other forcing hot magma up to the surface causing hot ‘soups’ of minerals and other chemical concoctions to erupt from chimney shape vents that are called black smokers, another chimney structure regularly found at these sites are white smokers.
These chimneys release hydrogen sulfide into the water creating very acidic conditions. the minerals and chemicals expelled from these chimneys eventually hardens around the chimney’s exterior and makes the chimneys larger and larger as more minerals build until they have reached a point in which the minerals available run too low to do so. the vent sites themselves are finite environments and have a lifespan of twenty to thirty years this is due to the vents ceasing to produce the mineral substance on which the vent communities depend.
Absence of Light
At around 200 meters in depth photosynthesis becomes almost impossible due to the decrease in light conditions but at 2,500 meters or greater where Hydro-thermal vents are found the presence of light is completely and absent so photosynthesis is in fact impossible, the presence of ‘marine snow’ or dissolved organic matter is also rare as they do not sink far enough due to the great depths at which vent sites are found this means that organisms living within this environment need a different way in which to grow and feed. The most common way organisms do this is to ‘chemosynthesise‘ where organisms will host sulfide or other mineral fixing bacteria in their cells that provide energy through transforming these minerals emitted from the vents themselves, More than 250 different types of chemosynthesising bacteria have been found at deep-sea vent environments which utilize sulfur, methane, hydrogen and other minerals to provide energy for other organisms.
Other ‘Pressures’ for Living at Depth
Not only is the absence of light a major problem that needs to be overcome by organism present at Hydro-thermal vents, these organisms face other factors that make this habitat hostile to most other organisms.
One of these major factors is the variability in temperature at the sites, due to their depth the surrounding water is extremely cold and can reach well into the minus figures but the water laden with the before mentioned minerals expelled from the chimneys can exceed well above 400 degrees Celsius creating an environment with two very extreme temperatures making it difficult for any organism to survive to due to the effects that temperature has on biological processes that happen within organisms
Another one of these environmental pressures is that of acidification. due to the nature of the white smokers present at hydro-thermal vent sites pumping out hydrogen sulfide in high concentrations the surrounding water is highly acidic in a study at the Galapagos rift placed metal at the opening of a vent and the metal was ‘attacked’ vigorously by the acidic seawater emanating from the vent and also by Arcobacteria (a chemosynthesising bacteria at the site) and disintegrates considerably within less than 10 days!
Pressure is also another larger factor to consider when studying these organisms at hydro-thermal vent sites due to the great depth at which the habitats are found, at the specific first site found in 1977 the vent sites pressure exceeded 240 atmospheres, The effects that pressure can have on organisms at depth is on protein structure and function as well as effects on membrane structure and function.
although the environments may seem extreme to us and incredibly inhospitable to many other organisms the organisms that live there wouldn’t be able to survive anywhere else, they specific needs and requirements that are only met through living at the vent sites. As well as evolving to include chemosynthesising bacteria in their cells vent organisms have other important adaptations that allow them to survive in their very specific environments. one species Riftia pachyptila completely lacks a mouth and digestive system and obtain their energy through vascularised gills called the obturacula which contain large mounts of blood vessels or hemoglobin that allow for resistance to varying oxygen levels at depth.
Another adaptation that can be observed through study is that organisms at this depth have developed more complex lipid (fatty) membranes to their cells in order to cope with the large amounts of hydro-static pressure, these complex membranes are coined as a ‘Homeoviscous adaptation’. bring these organisms to the surface though and they cannot cope with the low pressures inhibiting movement and functions.
Adaptations for the high temperature variations seen at hydro-thermal vents have been limited to studies of respiratory proteins, and enzymesand shows that the species Bythograea thermydon can slow its heart rate to cope with temperatures of 35°C but only for a short duration of time, another adaptation to temperature is seen in Pompeii worms (Alvinella pompejana) where they build U-shaped tubes with both the anterior and posterior end of the tube extending into the water column and the middle part fixed to the exterior of black or white smokers meaning only the middle part in exposed to higher temperatures.