Cold Seep Communities

Satellite photo of the Nile

Cold seeps are deep-sea environments, usually a few square meters in size, where fluid is released through slow diffusion from the sea floor. Mud volcanoes, which are active areas of fluid seepage, are other extreme environments discovered in the 1990s. These harsh conditions give rise to some of the most extreme and scientifically challenging environments for life to exist on the planet.

Extensive fields of hydrocarbon-rich gas seepage, mud volcanoes and pockmarks have all been mapped by the EUROCORES programme EUROMARGINS. On 4 – 6 October 2006, scientists from 50 different research groups in 12 different countries came together in Bologna, Italy to discuss future cross-discipline, pan-European and pan-World research following in the footsteps of this four year programme as EUROMARGINS is coming to an end.

Collaboration in the cold

As ocean sediments compact in cold seeps, fluids ooze out of the sediment and into the water. The cold-seep fluids contain chemical compounds produced by the decomposition of organic materials or by inorganic chemical reactions which occur at high temperatures and pressures.

Near cold seeps in the Eastern Mediterranean, Sbastien Duperron from Universit Pierre et Marie Curie in France has found unique bacterial symbiosis with mussels. Symbiotic associations between bivalves (mussels) and bacteria allow the former to benefit from the bacterias ability to chemosynthetically (without light) derive energy from the chemical compounds produced and use this energy to ensure primary production.

In the bivalve species Idas sp., we have found an association with six different symbionts. This is the widest diversity of symbionts ever described in a bivalve species, said Duperron.

This means that the mussel, depending on which type of symbionts it carries, can derive its energy from either sulphide or methane. In addition, Duperron has also found that in the Idas sp., three of the symbionts belong to bacterial groups previously not reported to include symbiotic bacteria. They seem to provide their hosts with nutrient from a yet unidentified source.

In parts of Monterey Bay, sulfide seeps up through the muddy seafloor. Clams living in the mud absorb this toxic chemical through their feet. The clams carry the sulfide to bacteria living inside their bodies. The bacteria use the sulfide to make food, which in turn provides nutrients for the clams. These are having size upto 4 inches (10 cm) or larger. Credit: All the Sea

But life in these alien environments can also exist without symbionts as Ian MacDonald from Texas A&M University, Corpus Christi US has demonstrated. His observations of the fauna around coastal margin hydrocarbon seeps in the Gulf of Mexico have revealed a habitat rich in biological activity and without a need for symbionts to extract nutrients.

MacDonald found that the productivity of deep-water seeps is overwhelmingly based on chemosynthesis (deriving energy from chemical compounds instead of light) and also some chemoautotrophic symbiosis (using a symbiont to derive energy from chemical compounds). However some communities of deep-sea corals associated with many seeps are probably filter feeders. Recent research findings indicate that the corals around the seeps may be much more widespread at seeps than previously realised. This fact adds to the biological diversity and ecological complexity of seep communities.

Underwater mud volcanoes

In the Nile deep-sea fan, mud volcanoes were discovered in the mid-1990s and they are still being investigated by a EUROMARGINS project. In the Gulf of Cadiz, the first mud volcanoes were discovered in 1999. The deepest mud volcano in this area is located at 3890m.

Luis Pinheiro from the University of Aveiro in Portugal participated in the 1999 cruise when mud volcanoes were first discovered. Pinheiro and his team have been investigating this area in close collaboration with Spain, France and Belgium. So far they have mapped 40 mud volcanoes, some as big as over 4km across and a few hundred meters high supporting characteristic ecosystems with particular faunal communities, living directly or indirectly on methane, some of which appear to represent completely new species to science.

Understanding how life survives and evolves in harsh environments on Earth like deep-sea cold seeps and mud volcanoes is an import goal for astrobiologists. The unique organisms found in these environments could be excellent analogs for how life could survive in other locations in our solar system.


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