Marine life flourishes in pitch black

A rich and surprisingly diverse array of marine animals has been discovered living in total darkness in the deepest parts of the Atlantic where no sunlight ever penetrates.

They range from a giant octopus-like creature with eight legs and fins that flap like an elephant's ears to tiny crustaceans that shine like gold-encrusted jewels.

Marine biologists have been astonished by the range of animals they have found during an underwater expedition that took them down 5000m where they have now identified 17,650 deep-sea species.

One of the most surprising animals was a rare specimen of a primitive creature called a cirrate, or finned octopod, commonly called a "Dumbo" because they swim by flapping a pair of ear-like fins, rather like the Disney cartoon character.

But the particular species the biologists found is now called "Jumbo Dumbo", because it grows up to 2m long and weighs about 6kg, the largest specimen of the type ever discovered, according to the Census of Marine Life, the umbrella group overseeing the global survey of the oceans.

The Dumbos were found between 1000m to 3000m down on the mid-Atlantic ridge, a vast chain of underwater mountains that stretch north and south along the seabed.

Samples of mud contained a surprisingly rich collection of fauna. Most of these animals are only a few millimetres in size, and they live on the sediment that falls from above, ranging in size from dead plankton to the residue of the carcasses of whales.

"To survive in the deep, animals must find and exploit meagre or novel resources, and their great diversity in the deep reflects how many ways there are to adapt," said Robert Carney of Louisiana State University, a co-leader of the deep-sea project.

"There is both a great lack of information about the 'abyss' and substantial misinformation. Many species live there. But the abyss has long been viewed as a desert. Worse, it was viewed as a wasteland where few to no environmental impacts could be of any concern."

The scientists used autonomous, unmanned submarines to explore the deepest reaches of the ocean floor, extending down several kilometres.

At between 2000m and 2500m, they found a bizarre, elongated orange fish-like animal called Neocyema, only the fifth specimen of the species to be caught. Another slow-growing fish living in complete darkness, called a rat-tail, was found at similar depths feeding on crustaceans.

The scientists also collected about 680 specimens of microscopic animals called copepods, which live in the plankton, but they were able to identify only seven of them. The rest appeared to be new to science including one that shone like a jewel with a golden sheen when illuminated.

"The distribution of species in the deep sea is full of mysteries," said Dr David Billett of the National Oceanography Centre in Southampton.

"The abyssal fauna is so rich in species diversity and so poorly described that collecting a known species is an anomaly. Describing for the first time all the different species in any coffee cup-sized sample of deep-sea sediment is a daunting challenge."

Mireille Consalvey, of NZ's Niwa, said the conditions were difficult, with many scientists struggling with seasickness amid high winds and 9m swells.

- INDEPENDENT