The abyssal world: Last terra incognita of the Earth surface

Date:
February 4, 2022
Source:
MARUM - Center for Marine Environmental Sciences, University
of Bremen
Summary:
The first unified vision of the world ocean biodiversity, based on
analysis of DNA sequences from the surface to deep-ocean sediments,
unveils the rich and unknown life in the abyssal realm, the last
terra incognita of the Earth surface. This collective effort was
made possible by 15 international deep-sea expeditions.



FULL STORY ==========================================================================
The first unified vision of the world ocean biodiversity, based on
analysis of DNA sequences from the surface to deep-ocean sediments,
unveils the rich and unknown life in the abyssal realm, the last terra incognita of the Earth surface. This collective effort was made possible
by 15 international deep-sea expeditions, including scientists from MARUM.


==========================================================================
The deep-ocean floor is the least explored ecosystem on the planet,
despite covering more than 60% of the Earth surface. Largely unknown
life in abyssal sediments, from benthic animals to microbes, helps to
recycle and/or sequester the sinking (in)organic matter originating
from pelagic communities that are numerically dominated by microscopic plankton. Benthic ecosystems thus underpin two major ecosystem services
of planetary importance: the healthy functioning of ocean food-webs
and the burial of carbon on geological timescales, both of which are
critical regulators of the Earth climate. Researchers from the Norwegian Research Centre (NORCE), Bjerknes Centre for Climate research, the
University of Geneva, as well as from the CNRS/Genoscope and IFREMER in
France, have massively sequenced eukaryotic DNA contained in deep-sea
sediments from all major oceanic basins, and compared these new data
to existing global-scale plankton datasets from the sunlit and dark
water column, obtained by the Tara Oceans and Malaspina circumglobal expeditions. This provides the first unified vision of the full ocean eukaryotic biodiversity, from the surface to the deep- ocean sediment,
allowing marine ecological questions to be addressed for the first time
at a global scale and across the three-dimensional space of the ocean, representing a major step towards "One Ocean ecology." "With nearly 1700 samples and two billion DNA sequences from the surface to the deep-ocean
floor worldwide, 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," says Tristan Cordier, Researcher at NORCE and Bjerknes Centre for Climate Research,
Norway, and lead author of the study.

What lives in this dark and hostile environment? By comparing sediment
DNA sequences with the ones from pelagic realms, it was possible to
distinguish indigenous benthic organisms from sinking plankton that had
reached the seafloor from the overlying water column. Results indicate
that this benthic biodiversity could be three times larger than in the
water masses above; and this diversity is composed of very different
taxonomic groups that are mostly unknown.

"We compared our deep-sea benthic DNA sequences to all references
sequences available for known eukaryotes. Our data indicates that nearly
two third of this benthic diversity cannot be assigned to any known group, revealing a major gap in our knowledge of marine biodiversity," says Jan Pawlowski, Professor at the Department of Genetics and Evolution of the University of Geneva and at the Institute of Oceanology of the Polish
Academy of Sciences in Sopot.



==========================================================================
What can plankton DNA in deep-sea sediments tell us? Analysis of the
abundance and composition of plankton DNA in deep-sea sediments confirmed
that polar regions are hotspots of carbon sequestration. Moreover, the composition of the plankton DNA in sediments predicts the variation of
the strength of the biological pump, an ecosystem process that transfer atmospheric carbon dioxide into the deep ocean, hence regulating the
global climate.

"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," says Colomban de
Vargas, Researcher at CNRS in Roscoff, France.

How will the deep-sea be impacted by global changes? This genomic dataset represents the first consistent snapshot of whole eukaryotic diversity in
the modern ocean. It provides a unique opportunity to reconstruct ancient oceans from the DNA contained in the cumulative sediment record, to assess
how climate has impacted plankton and benthic communities in the past.

"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
modelling the future carbon cycle under climate change," explains
Tristan Cordier.

"Our study further demonstrates that deep-sea biodiversity research
is of paramount importance. 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," concludes Andrew J. Gooday, Emeritus
Fellow at the National Oceanography Centre, Southampton, who was also
involved in the research.

========================================================================== Story Source: Materials provided by MARUM_-_Center_for_Marine_Environmental_Sciences,
University_of_Bremen. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Tristan Cordier, Ine`s Barrenechea Angeles, Nicolas Henry, Franck
Lejzerowicz, Ce'dric Berney, Raphae"l Morard, Angelika Brandt,
Marie-Anne Cambon-Bonavita, Lionel Guidi, Fabien Lombard, Pedro
Martinez Arbizu, Ramon Massana, Covadonga Orejas, Julie Poulain,
Craig R. Smith, Patrick Wincker, Sophie Arnaud-Haond, Andrew
J. Gooday, Colomban de Vargas, Jan Pawlowski. Patterns of eukaryotic
diversity from the surface to the deep- ocean sediment. Science
Advances, 2022; 8 (5) DOI: 10.1126/sciadv.abj9309 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220204145230.htm

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