A diet of methane and sulphur
Found alongside these methane gas seeps are communities of clams that use the gas as a source of food. They don't actually eat the gas but they have evolved to harbour bacteria in their tissues that do the job for them.
These organisms are known as 'chemosymbiotic' and a few groups of clams have been very successful in adapting to this environment.
The same group of clams can also exploit sulphur and these are found living in areas where there are layers of rotting vegetation, around decaying whale carcasses, at hot vents and even on mud contaminated with diesel oil.
Because these clams come from unusual environments and often from deep water, many have yet to be studied in detail. A number of these gas guzzling clams have been sent to Amgueddfa Cymru - National Museum Wales for identification and description.
Clams from Chile
Clam shells and live specimens have been sent to the Museum following the discovery of a methane seep off the coast of Chile at a depth of 700-900m.
One such species, in a group known as Thyasira, was new to science. The bacteria in the gill tissue of the clam were studied using a scanning electron microscope. This confirmed the symbiosis (reliance) between the bacteria and the clam.
A species of the genus Lucinoma was also discovered to be new to science but only shells have been found so far. It is likely that the majority of species living at this site are endemic (restricted to this location) and found nowhere else in the world.
The Pakistan Margin
From the other side of the world, we have been sent a small species of Thyasira from the Indus Fan, off the coast of Pakistan, collected while investigating the unusual fauna that live in the very low oxygen waters of this region.
This tiny clam was found in densities up to 500/square metre and was undoubtedly exploiting the abundant food. It is another unstudied genus, and the Museum is working with the Natural History Museum, London, who are investigating the molecular (DNA) systematics of the group.
A clam with a taste for shipwrecks
Man-made sources of methane and sulphur are also exploited and one of the strangest was the cargo of the sunken container ship Francois Vieljeux. This ship sank off the north coast of Spain in 1,160m of waters, taking with it its cargo of castor beans and sunflower seeds.
During attempts to salvage the vessel it was noted that clams had settled and grown on the cargo. All the clams belonged to chemosymbiotic groups and were exploiting the sulphur released by the rotting cargo. One clam was a Thyasira, similar to the specimen from Chile.
Cascadia Basin, off Washington State
The Baby Bare Seamount in the north-east Pacific Ocean is a hot spring and home to a new species of Axinus (similar to Thyasira). This site is unusual in that no other species of bivalve typically found at other methane seeps and hot vent sites are found here. Methane and Hydrogen sulphide levels are low, so initially it was a mystery as to what these animals were using as nutrition.
Cadiz Mud Volcanos
Off the Southern coast of Portugal there are numerous marine mud volcanoes created by stresses on the African and Eurasian tectonic plates. These stresses cause hot, methane and sulphur rich fluids to eject from deep within the volcanoes out into the sea bed above. By the time the fluids reach the sediment surface they are cold, so the mud volcanoes are classed as cold-seeps. Many species of Thyasira clams are found at some of these sites, but only a few are known to harbour the chemosymbiotic bacteria that help them to extract nutrition from sulphur and methane. A collaboration between the Museum and Cadiz University, Spain has resulted in the newly described species Thyasira vulcolutre , meaning 'belonging to mud volcano'.
Finally, in conjunction with Bangor University, the Museum is carrying out the taxonomic work on a Thyasira collected from a mud volcano in the Arctic and a mussel of the genus Idas which was collected from diesel contaminated mud beneath an oil rig in the North Sea.
This work by Amgueddfa Cymru - National Museum Wales is helping research the possibility of using these clams to clean up contaminated areas of the sea bed.
Article Date: 1 April 2008
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SEM (Scanning Electron Microscope)
A microscope that uses a finely focused electron beam scanned across a sample to produce high resolution images. A SEM can resolve much smaller feature than a standard microscope, down to approximately 2 nanometers.
Or deoxyribonucleic acid, is a long double-helix molecule that carries the genetic code for a species.