Next To RocksBack To SoundLiving on the Seafloor

Life at the bottom of the oceans

Life on the deep ocean floor must deal with extreme conditions.  It is almost always completely dark, very cold, salty, and highly pressurized.  Before scientists found the first deep-sea hydrothermal vent, it was thought that life on the deep seafloor was diverse and long-lived, but that the abundance of animals was very low.

Hydrothermal vents

Drawing of ALVIN and tube worms.These ideas changed dramatically in the 1970's when the first hydrothermal vents were discovered in the Pacific ocean. They were found during an ALVIN dive at the East Pacific Rise, a mid-ocean ridge where tectonic plates spread apart and molten rock rises from within the Earth to form new oceanic.  The illustration at the left shows ALVIN and its lights illuminating hydrothermal vents and the animals that live near them.

Black smokersSeawater circulates within the newly formed crust, becomes superheated, and then rises back to the seafloor.  This very hot water (350 degrees C or 650 F) jets upwards out of the crust into the cold water. The places where the hot water comes out are called hydrothermal vents. When the scalding hot water meets the very cold seawater beyond the vent, an assortment of dissolved metals often precipitates out forming small particles in the water.  These types of vents are called black smokers, and three black smoker chimneys are shown in the picture on the right.

Tube worms and crabWhat was truly amazing about hydrothermal vents was that clustered around them were dense colonies of large, previously unknown animals such as tube worms, giant clams, and other strange animals.  Tube worms can be 3 to 4 meters (9 to 12 feet) long, and thus when stretched out much taller than the height of an average person.

Chemosynthesis versus photosynthesis

Vent communitySince there is no sunlight at deep-sea hydrothermal vents, plants can not grow, and what puzzled scientists for a long time was what the animals were eating. The sea water near hydrothermal vents is full of hydrogen sulfide, carbon dioxide, and oxygen, and it was discovered that special bacteria could live off of the hydrogen sulfide, and that these bacteria form the base of the food chain.  The bacteria produce organic molecules which the larger vent animals live on.  The picture on the left shows the diversity of life found at these vents.

Life on the Puna Ridge

We do not know if there are active hydrothermal vents at the Puna Ridge.  It depends on whether there is a source of heat in the crust (such as hot molten rock) that will raise the temperature of the seawater.  Using the DSL-120 kHz side-scan sonar data and ARGO II photographs of the seafloor, we will look for evidence of hydrothermal vents in the our study area.  If there are active hydrothermal vents than there will almost certainly be life. 

Test Your Understanding

Hydrothermal vents stop and others start. New vents may be a long way away from old vents.  How do animals get to new hydrothermal vents?

Check your answer below to see if you are correct.

the animals swim to the new vents
the animals are already there when the new vent starts
larvae (young animals) get carried on water currents to new vents