Extreme environments: Hydrothermal vents

  • The deep ocean floor is largely desolate, devoid of much of the life that flourishes in shallower waters.
  • Known as the abyssal plain, these areas cover over half of the Earth’s surface.
  • However, amidst the barren seabed of the deep, smoking pillars of minerals rise from the floor, teeming with life.
  • These pillars are called hydrothermal vents, and they provide the deep-sea environment a vital source of nutrients that support a unique assemblage of microbes and animals that would otherwise not exist.

In the 1970s, surveys of the East Pacific Rise, where the eastern edge of the Pacific tectonic plate is moving away from its neighbouring plates, led to a unique discovery. On the otherwise barren lava flows of the Galápagos Rift, at depths of about 2,500m, dense communities of clams and mussels were found surrounding fissures emitting hot, cloudy water. The scientists conducting the surveys had discovered a hydrothermal vent, which, like an oasis in the desert, is an area of unusually high biological activity in an otherwise largely unproductive ecosystem.

Like geysers on land, hydrothermal vents form in areas of high volcanic activity, particularly near the edges of tectonic plates. Cracks and fissures form on the seabed, where water comes into contact with the magma below the surface. The water is heated by the molten rock and then shoots out of the fissure in a cloud of high-temperature, toxic minerals from the crust. These minerals tend to deposit around the fissure and eventually form a pillar, resembling a smoking chimney. You might imagine that it would be difficult to live at temperatures of 60–464 °C, without light, surrounded by sulphurous minerals, but it is these properties that allow hydrothermal vents to support a unique array of life deep in the sea.

The species living within the vicinity of hydrothermal vents have developed unique adaptations and behaviours that are very rarely seen in other habitats.

Owing to the extreme conditions, the species living within the vicinity of these vents have developed unique adaptations and behaviours that are very rarely seen in other habitats. While algae and plants can be found at the bottom of shallow water and terrestrial food webs, chemotrophic bacteria are the primary producers at hydrothermal vents. They convert the minerals being emitted into carbohydrates that serve as a food source for crustaceans and molluscs, like those found surrounding the first-discovered vents in the eastern Pacific. These species then become food for larger animals, such as octopuses and fish.

Hydrothermal vents form in areas of high volcanic activity, particularly near the edges of tectonic plates.

In addition to this typical producer–grazer–predator dynamic that is common in less extreme habitats, some species surrounding hydrothermal vents gain their nutrition through more unique means. The scaly-foot gastropod, for example, is a peculiar sea snail that lives only in hydrothermal vents in the Indian Ocean. The outer layer of its shell is formed from iron sulphides and its fleshy foot is covered with iron-containing scales, giving it an odd, armoured appearance. The metallic exterior is not its only distinguishing feature; while most snails are either grazers or predatory, the scaly-foot gastropod does not eat at all! Instead, symbiotic chemotrophic bacteria that reside in a gland within the snail’s body convert the chemicals released by the vents they live on into energy, supporting their snail host.

Although the deep-sea environment is home to a wide variety of unique creatures, few areas in the deep are as rich and diverse as those surrounding hydrothermal vents. Supported by bacteria that are able to convert minerals into energy, pockets of unique animals form with adaptations that allow them to withstand and even thrive under the extreme conditions of their habitat.

Rachel Herbert-Goddard is a freelance writer based in the UK.

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