Deep Down in the Sea: A Lost World
Deep down under the sea is another universe of sheer blackness hidden from the sun. Yet a busy blackness in some cases. Communities of species previously unknown to science have been discovered on the seafloor near Antarctica, clustered in the hot, dark environment surrounding hydrothermal vents. The discoveries, made by teams led by the University of Oxford, University of Southampton and British Antarctic Survey (BAS), include new species of yeti crab, starfish, barnacles, sea anemones and an octopus.
For the first time, researchers used a Remotely Operated Vehicle (ROV) to explore the East Scotia Ridge deep beneath the Southern Ocean, where hydrothermal vents, (including black smokers reaching temperatures of up to 382 degrees Celsius) create a unique environment that lacks sunlight, but is rich in certain chemicals. The team reports its findings in this week’s issue of the on-line journal PLoS Biology.
Normally stormy and cold, this sea is the area of water between Tierra del Fuego, South Georgia, South Sandwich Islands, South Orkney Islands and the Antarctic Peninsula, and bordered on the west by Drake Passage. These island groups all sit on top of the Scotia Ridge.
"Hydrothermal vents are home to animals found nowhere else on the planet that get their energy not from the Sun but from breaking down chemicals, such as hydrogen sulfide," said Professor Alex Rogers of Oxford University’s Department of Zoology, who led the research. "The first survey of these particular vents, in the Southern Ocean near Antarctica, has revealed a hot, dark, lost world in which whole communities of previously unknown marine organisms thrive."
Highlights from the ROV dives include images showing huge colonies of the new species of yeti crab, thought to dominate the Antarctic vent ecosystem, clustered around vent chimneys. Elsewhere the ROV spotted numbers of an undescribed predatory sea-star with seven arms crawling across fields of stalked barnacles. It also found an unidentified pale octopus, nearly 2,400 meters down, on the seafloor.
"What we didn’t find is almost as surprising as what we did," said Professor Rogers. "Many animals such as tubeworms, vent mussels, vent crabs, and vent shrimps, found in hydrothermal vents in the Pacific, Atlantic, and Indian Oceans, simply weren’t there."
Life has traditionally been seen as driven by energy from the sun, but deep sea organisms have no access to sunlight, so they must depend on nutrients found in the dusty chemical deposits and hydrothermal fluids in which they live. Previously, benthic oceanographers assumed that vent organisms were dependent on marine snow, as deep sea organisms are. This would leave them dependent on plant life and thus the sun. Some hydrothermal vent organisms do consume this rain, but with only such a system, life forms would be very sparse. Compared to the surrounding sea floor, however, hydrothermal vent zones have a density of organisms 10,000 to 100,000 times greater.
Hydrothermal vent communities are able to sustain such vast amounts of life because vent organisms depend on chemosynthetic bacteria for food. The water that comes out of the hydrothermal vent is rich in dissolved minerals and supports a large population of chemo-autotrophic bacteria. These bacteria use sulfur compounds, particularly hydrogen sulfide, a chemical highly toxic to most known organisms, to produce organic material through the process of chemosynthesis.
The team believe that the differences between the groups of animals found around the Antarctic vents and those found around vents elsewhere suggest that the Southern Ocean may act as a barrier to some vent animals. The unique species of the East Scotia Ridge also suggest that, globally, vent ecosystems may be much more diverse, and their interactions more complex, than previously thought.
BAS author Dr Rob Larter explains how complex it is to operate the ROV at depth. "Beneath 2.5 km of water it is totally dark and the lights on the remotely operated vehicle only give a few meters visibility. Therefore it was essential to have detailed maps of the sea bed to navigate the vehicle around the vent sites. At the start of the project we had low resolution maps of the sea bed topography from work done by BAS in the 1990s."
For further information and photo: http://www.antarctica.ac.uk/about_bas/news/news_story.php?id=1688