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The Mid-Atlantic ridge is the zone running north to south along the bed of the Atlantic Ocean where two major tectonic plates are gradually moving apart, causing volcanic and other geological activity.  As the plates separate slowly, the rock fractures and sea water becomes heated by contact with hot and molten rock below the surface.  This hot water dissolves minerals and contains highly concentrated levels of a range of chemical substances. 

In places this water is forced from hydrothermal vents on the bed of the sea, forming plumes of superheated hot water that rise into the ocean, sometimes carrying thick black particulates.  As the water cools slightly at the vent, various dissolved chemicals are deposited to make large mineral structures such as chimneys and other forms. Exploration of this environment has been increasing over the past forty years with the development of advanced equipment and remotely-operated vehicles: small submarines that carry sophisticated scientific probes and cameras.

The bottom of the ocean is not generally fertile in comparison to coastal seas, but hydrothermal vents are home to dense populations of animals, supported by bacteria that flourish in the chemical-rich waters. The high sulphur and mineral content of the water would make it toxic to most organisms, but some species have evolved to tolerate the temperature and chemical environment.  The animals either consume the bacteria (or one another) directly, or have, in the case of bivalve mussels, symbiotic bacteria in their gill tissue that enables them to use sulphur compounds to produce energy.  These environments are small islands of fertility on the ocean floor, of great evolutionary and ecological interest.

Dr Adrian Glover (Zoology) is part of a team of co-authors in an international team from Portugal, France and the UK who have recently described assemblages of animals from the 11m-high Eiffel Tower structure in the Lucky Strike hydrothermal vent field 1700 metres deep on the Mid-Atlantic Ridge, just to the south of the Azores. Pictures of the Eiffel Tower can be seen on the IFREMER site.

They sampled temperature and sulphide were measured in the water at two different assemblages: one dominated by shrimps and the other by mussels. Temperature, rather than sulphide concentration, appeared to be the major environmental factor affecting the distributions of the resident hydrothermal vent species. The highest temperature variability and the highest maximum recorded temperatures were found in the assemblages visibly inhabited by alvinocaridid shrimp and dense mussel beds of large Bathymodiolus azoricus, whereas the less variable and more stable habitats were inhabited by smaller-sized mussels with increasing bare surface in between.

 

D Cuvelier et al. (2011) Hydrothermal faunal assemblages and habitat characterisation at the Eiffel Tower edifice (Lucky Strike, Mid-Atlantic Ridge). Marine Ecology (2011) doi:10.1111/j.1439-0485.2010.00431.x.

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