Census of Marine Life scientists have inventoried an astonishing abundance, diversity and distribution of deep sea species that live down to 5,000 meters (around 3 miles) below the ocean waves.

Revealed via deep-towed cameras, sonar and other 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 meager 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.

Edward Vanden Berghe, who manages the Census’ inventory of marine life observations, notes that the number of species recorded falls off dramatically at deeper depths – a function of the dearth of sampling in the deep sea.

While the collective findings are still being analysed for release as part of the final Census report to be released in London on 4 October 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 of the Census project
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.

At 1,000 to 3,000 meters (~.6-1.9 miles): NOAA researchers led by Mike Vecchione of
the Smithsonian Institution collected a very large specimen of a rare, primitive animal known as cirrate or finned octopod, commonly called “Dumbos” because they flap a pair of large ear-like fins to swim, akin to the cartoon flying elephant.

The jumbo Dumbo netted by Census explorers was estimated to be nearly two meters (~6 feet) long and, at 6 kg (~13 pounds), the largest of only a few specimens of the species ever obtained.

Altogether, nine species of gelatinous “Dumbos” were collected on the Mid-Atlantic
Ridge, including one that may be new to science. Scientists were surprised to find such a plentiful and diverse assemblage of these animals, which rank among the largest in the deep sea.

Further Reading:
Census of Marine Life

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