Below 300 m light becomes too dim to be used as an energy source and below 1000 m the water temperature drops below 5oC. The pressure at 3000 m is ~300 times the atmospheric pressure at the ocean surface yet life manages to thrive at hydrothermal vents (Van Dover, 2000).
Mid-Atlantic Ridge vent systems
The Mid-Atlantic Ridge (MAR) lies along the boundaries of two tectonic plates that are being pulled away from one another. Volcanically active areas where these plates are being pulled apart are known as spreading centres and are the sites where hydrothermal venting occurs (Fig. 2) (Grassle, 1986; Van Dover, 2000).
Deep sea shrimp (Rimicaris exoculata) live at between 1700 – 4088 m deep (Nye et al., 2011) on many of the vent sites that line the MAR such as those named TAG, Snake Pit and Lucky Strike (Nye et al., 2011). There are two types of hydrothermal vent systems that form along the MAR which differ in chemical composition and temperature. The two types are named after the colour of the particles that emanate from the vent opening, resembling billowing smoke; they are known as white smokers, that form under cooler conditions, and black smokers (Alt, 1995; Van Dover, 2000).
Shrimp swarm black smokers
Rimicaris exoculata have been recorded in swarms exceeding 3000 individuals m-2 surrounding black smokers on the MAR (Ravaux et al., 2003). Black smokers are formed at active tectonic margins by a process called hydrothermal convection (Fig. 3). Cold deep sea water percolates down through cracks in the sea bed and is heated as it nears the earth’s magma (geothermal heating) causing it to react chemically with the surrounding rock becoming enriched in metals and sulphide (Van Dover et al., 2002). The water is heated to extreme temperatures exceeding 400oC which causes the water to become buoyant and rise rapidly back to the surface of the ocean crust. The super-heated water is expelled from the seabed in a plume of particles resembling black smoke that forms as the metals and sulphide precipitate (solidify) as they are rapidly cooled by the near freezing seawater (Alt, 1995; Van Dover, 2000).
The hydrothermal vent systems are clearly harsh and complex environments but to sustain life there must be a source of food. Sun light is the building block of life on earth so how is it that life is able to flourish beyond its reach? The answer comes from the extremely hot, chemically enriched fluid that emanates from the hydrothermal vents. In the next section of my blog I will look into what R. exoculata feed on and the methods it uses to extract energy from the hydrothermal fluid through its special relationship (epibiosis) with bacteria that live on the surface of its gills.
Next up – Feeding