How much do we actually know about the wide range of species in the world’s oceans? How do they co-exist and interact with other species? And do they contribute to human life and climate change?
These are just some of the significant questions a team of international scientists posed when they embarked on a multi-year journey – the “Tara Oceans” project – to explore the world’s major oceans aboard the French schooner “Tara” in 2009.
The “Tara Oceans” expedition brought together accomplished scientists from all over the world to travel across the globe from 2009-2013. “This is the largest DNA sequencing effort ever done for ocean science,” said Patrick Wincker, from Genoscope, CEA.
In fact, the team collected a total of 35,000 samples of plankton, including viruses, microbes and microscopic eukaryotes – organisms with complex cells, from single-cell algae to fish larvae – from major oceanic regions.
As part of Tara Oceans’ unique “eco-systems biology” approach, the expedition team also sampled other domains of life, like animals, and collected a rich variety of environmental data in relation to the 35,000 plankton samples.
“In terms of eukaryotes, we sequenced nearly a billion genetic barcodes, and found that there is a greater variety of single-cell eukaryotes in plankton than was thought,” said Colomban de Vargas, from Centre National de la Recherche Scientifique (CNRS). “They appear to be much more diverse than bacteria or animals, and most belong to little-known groups.”
The Results and Discoveries
“When you mention rich ecosystems that are vital for life on Earth, people tend to think of rainforests,” Tara Oceans’ official press release explained; “but ocean plankton are actually just as crucial.”
“The microscopic beings that drift on the upper layer of the oceans are globally referred to as “plankton”; together they produce half of our oxygen, act as carbon sinks, influence our weather, and serve as the base of the ocean food web that sustains the larger fish and marine mammals that we depend upon or draw delight from.”
Even though the scientific community has learned a lot about plankton over the years, it turns out that these organisms are far more complex than anyone ever imagined. Here is what we know now thanks to the Tara Oceans project:
A Plethora of Unknown Species and Genes
Analyses of the 35,000 samples “revealed around 40 million genes, the vast majority of which are new to science, thus hinting towards a much broader biodiversity of plankton than previously known,“ said Patrick Wincker, from Genoscope, CEA, about the findings that will inspire a new era of how scientists will study the oceans.
In terms of viruses, Tara Oceans found more than 5,000 viral populations throughout the upper parts of the ocean. “Surprisingly despite several decades of prior marine viral research, only 39 of these 5,000 viral populations were similar to previously known viruses,” said Jennifer Brum, researcher at the University of Arizona.
Interaction Between Species
“When we mapped how planktonic organisms – from viruses to small animal larvae – interact with each other, we discovered that most of those interactions are parasitic, recycling nutrients back down the food chain,” said Jeroen Raes from VIB, KU Leuven, and Vrije Universiteit Brussel.
Scientists were able to create new computer models that helped in predicting how diverse planktonic organisms interact, which was then confirmed via selective microscopy observations.
“This map is a first step towards a better understanding of the dynamics and structure of the global marine ecosystem,” according to Tara Oceans’ press release.
Impact on Climate Change
“We found that, at depths still reached by sunlight, temperature was the main factor that influences the composition of prokaryotes (bacteria and archaea) communities. Different sets of organisms come together depending on the water temperature,” says Peer Bork from the European Molecular Biology Laboratory.
“The finding that temperature shapes which species are present, for instance, is especially relevant in the context of climate change, but to some extent this is just the beginning,” Chris Bowler, from CNRS, says about understanding the distribution and interactions of plankton, which will help build predictive models to study climate change.
“In view of the Climate Conference in Paris in 2015 (COP21), it is important to understand that plankton biodiversity affects our climate through its ability to store carbon dioxide over large time scales,” Romain Troublé, secretary general of Tara Expeditions, added.
For scientists who are interested in the analysis of 7.2 terabases of metagenomic data, AAAS/ Science has made available the “Ocean Microbial Reference Gene Catalog” right here. And if you would like to see more pictures of the expedition, head over to the official site here.