This unfamiliar Dumbo species collected by Census of Marine Life scientists on a 2009 MAR-ECO voyage to the Mid-Atlantic Ridge may prove new to science. Photo: David Shale, MAR-ECO, Census of Marine LifeDeep sea teeming with species that have never known sunlightCensus of Marine Life scientists have inventoried an astonishing abundance, diversity and distribution of deep sea species that have never known sunlight - creatures that somehow manage a living in a frigid black world down to 5,000 meters below the ocean waves.
Revealed via deep-towed cameras, sonar and other vanguard technologies; animals known to thrive in an eternal watery darkness now number 17,650; a diverse collection of species ranging from crabs to shrimp to worms. Most have adapted to diets based on meagre droppings from the sunlit layer above, others to diets of bacteria that break down oil, sulphur and methane, the sunken bones of dead whales and other implausible foods.
Five of the Census' 14 field projects plumb the ocean beyond light, each dedicated to the study of life in progressively deeper realms - from the continental margins (COMARGE: Continental Margins Ecosystems) to the spine-like ridge running down the mid-Atlantic (MAR-ECO: Mid-Atlantic Ridge Ecosystem Project), the submerged mountains rising from the seafloor (CenSeam: Global Census of Marine Life on Seamounts), the muddy floor of ocean plains (CeDAMar: Census of Diversity of Abyssal Marine Life), and the vents, seeps, whale falls and chemically-driven ecosystems found on the margins of mid-ocean ridges and in the deepest ocean trenches (ChEss: Biogeography of Deep-Water Chemosynthetic Systems).
Edward Vanden Berghe, who manages OBIS (Ocean Biogeographic Information System), the Census' inventory of marine life observations, notes that, unsurprisingly, the number of records in the database falls off dramatically at deeper depths – a function of the dearth of sampling done in the deep sea.
However, Dr. Vanden Berghe reports that OBIS today records 5,722 species for which all recorded observations are deeper than 1,000 meters (~.62 miles) and 17,650 species for which all recorded observations are deeper than 200 meters, the depth where darkness stops photosynthesis.
Scientists working on the deep-sea Census number 344 and span 34 nations.
By the time the 10-year Census concludes in October, 2010, the five deep-sea projects will have collectively fielded more than 210 expeditions, including the first ever MAR-ECO voyage in October-November this year, to explore the Mid-Atlantic Ridge south of the Equator, a scientific collaboration between Russia, Brazil, South Africa and Uruguay.
Each voyage is hugely expensive and challenged by often extreme ocean conditions and requirements that have kept the remotest reaches of Neptune's realm impenetrable until recently.
While the collective findings are still being analysed for release as part of the final Census report to be released in London on October 4, 2010, scientists say patterns of the abundance, distribution and diversity of deep-sea life around the world are already apparent.
"Abundance is mostly a function of available food and decreases rapidly with depth," says Robert S. Carney of Louisiana State University, co-leader (with Myriam Sibuet of France) of the Census project COMARGE, studying life along the world's continental margins.
"The continental margins are where we find the transition from abundant food made by photosynthesis to darkened poverty. The transitions display the intriguing adaptations and survival strategies of amazing species," says Dr. Carney.
Abundance in the deep sea requires one or more of the following:
•Swift current, which increases an animal's chance of encountering food;
•Long-lived animals, populations of which grow numerous even on a meager diet;
•Abundant food in higher layers that either settles to the depths or to which deep animals can migrate;
•An alternative to photosynthesis of food, such as chemosynthetic production.
"In the bathy- and mesopelagic zones - the largest 3D deep-sea living space - animals either have to cope somehow with food scarcity or migrate long distances up to find food," says MAR-ECO project leader Odd Aksel Bergstad of University of Bergen. "Because it provides an oasis of topographical relief in the center of the ocean, we found a high concentration of animals on the Mid-Atlantic Ridge."
"Distribution is pretty straightforward for animals in the deep sea," says Dr. Carney. "The composition of faunal populations changes with depth, likely a consequence of physiology, ecology and the suitability of seafloor habitat condition for certain animals."
"Diversity is harder to understand. Although the mud on the deep sea floor appears monotonous and poor in food, that monotonous mud has a maximum of species diversity on the lower continental margin. To survive in the deep, animals must find and exploit meager or novel resources, and their great diversity in the deep reflects how many ways there are to adapt."
