New details emerge about the mysterious underwater animals of the ocean floor

By Mark Waghorn via SWNS

The mysterious community of animals inhabiting the ocean floor may be three times more diverse than those roaming the waters above according to a biological survey of the planet's least explored area.

They are composed of very different organisms - most of which are unknown to science.

The discovery adds to evidence that we know more about space than the deep sea.

It is the least explored ecosystem on the planet - despite covering more than 60 percent of the Earth surface.

It is home to weird creatures ranging from microbes to giant jellyfish and octopus to shape-shifting whales and alien-like squid.

They are vital to the health of the planet - helping recycle and sequester sinking microscopic plankton.

Now an international team has mapped DNA from complex life forms, or eukaryotes, collected from sediments from all major oceanic basins.

It provides the first unified 3D vision from the waves to the seabed - representing a major step towards 'One Ocean ecology.'

Lead author Dr. Tristan Cordier, a researcher at the Norwegian Research Centre, Bergen, said: "There were nearly 1,700 samples and two billion DNA sequences.

"High-throughput environmental genomics vastly expands our capacity to study and understand deep-sea biodiversity, its connection to the water masses above and to the global carbon cycle."

By comparing those from the sediment and the open sea, it was possible to distinguish indigenous benthic organisms from plankton that had sunk from the overlying water column.

Benthic creatures are animals that live on the seafloor. The results indicate their biodiversity could be three times larger.

Co-author Professor Jan Pawlowski, of the University of Geneva, said: "We compared our deep-sea benthic DNA sequences to all references sequences available for known eukaryotes."

These comprise some single-celled life forms as well as all multi-cellular organisms - such as animals.

Added Prof Pawlowski: "Our data indicates that nearly two-thirds of this benthic diversity cannot be assigned to any known group, revealing a major gap in our knowledge of marine biodiversity."

The researchers describe the 'abyssal world' as the last 'terra incognita' on Earth - Latin for 'unknown land.'

The findings shed fresh light on what lives in this dark and hostile environment.

They are the result of 15 deep-sea expeditions across all major oceanic regions - including the Arctic and Southern Oceans.

Analysis of plankton DNA in deep-sea sediments confirmed polar regions are hotspots of carbon sequestration.

Moreover, the composition predicts variation of the strength of an ecosystem phenomenon dubbed the 'biological pump.'

It is key to the global carbon cycle - removing the gas from the atmosphere, changing it into living matter and distributing it to the deeper ocean.

Without it, the atmospheric concentration of CO2 would be much higher.

Co-author Dr. Colomban de Vargas, of the French National Centre for Scientific Research, Roscoff, said: "For the first time, we can understand which members of plankton communities are contributing most to the biological pump, arguably the most fundamental ecosystem processes in the oceans."

The genomic dataset is the most complete snapshot of life diversity in the modern ocean to date.

It also provides a unique opportunity to reconstruct ancient oceans from the DNA contained in the cumulative sediment record.

This is helping to assess how climate has impacted plankton and seabed communities in the past.

Dr. Cordier said: "Our data will not only address global-scale questions on the biodiversity, biogeography and connectivity of marine eukaryotes.

"It can also serve as a basis to reconstruct the past functioning of the biological pump from ancient sedimentary DNA archives.

"It would then inform on its future strength in a warmer ocean, which is key for modeling the future carbon cycle under climate change."

The study in Science Advances further underlines deep-sea biodiversity is of paramount importance in the face of global warming.

Co-author Prof Andrew Gooday, of the National Oceanography Centre, Southampton said: "Huge numbers of unknown organisms inhabit ocean-floor sediments and must play a fundamental role in ecological and biogeochemical processes.

"A better knowledge of this rich diversity is crucial if we are to protect these vast, relatively pristine ecosystems from the impacts of possible future human incursions and understand the effects on it of climate change."