ORONO — University of Maine oceanographers are part of a collaborative international team studying the microscopic world of plankton, according to a news release from UMaine.  During expeditions from 2009 to 2013 aboard Tara, researchers collected 35,000 samples from the world's oceans.

Data generated from the samples are providing unprecedented resources — including a catalog of several million new genes — expected to transform how oceans are studied and establish a global-scale baseline to evaluate the impact of climate changes on oceanic ecosystems.

In five articles in a special issue of Science to be published May 22, the interdisciplinary team maps the biodiversity of a range of planktonic organisms, exploring their interactions and how they impact and are affected by their environment, primarily temperature.

"The resources we've generated will allow us and others to delve even deeper, and finally begin to really understand the workings of this invisible world," said Chris Bowler from the Centre National de la Recherche Scientifique in the news release.

"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," said Bowler.

Tara is a 118-foot-long, 33-foot-wide, 120-ton research vessel operated by Tara Expeditions Foundation. Scientists from around the world collect samples from the Earth's oceans to understand climate change and to explain it simply.

"To act in ecology we shall have to relinquish our individualist world. It is the key. This is what we attempted and accomplished on Tara. A team's work at the service of the planet," said Tara Foundation President Etienne Bourgois on the website.

UMaine oceanographers Emmanuel Boss and Lee Karp-Boss are part of the science team and participated in six expedition legs. UMaine doctoral student Alison Chase took part in a four-week research venture from France to Norway during the summer 2013 Tara Oceans Polar Circle expedition.

Also, Ivona Cetinić, research associate at the University of Maine Darling Marine Center, participated in the Tara Oceans Polar Circle expedition. And Tom Leeuw, who earned a master's degree in oceanography at UMaine in 2014, took part in month-long projects aboard Tara in both the Polar Circle and Mediterranean.

Collaboration, said Boss, Karp-Boss and Chase, is one of several reasons why they relish taking part in the research aboard Tara and contributing to science.

Boss was chief scientist during two legs aboard Tara — in December 2011–January 2012 from Panama City, Florida to Savannah, Georgia and in 2013 in the Western Arctic. In 2014, he conducted research in the Mediterranean Sea during a voyage from Cyprus to Malta. His lab installed a system aboard the vessel that collected optical data about ocean particles from 2009 to 2013.

Karp-Boss served as chief scientist on voyages from Chile to Easter Island in 2011, from New York to Bermuda in 2012 (she spoke with United Nations Secretary-General Ban Ki-moon prior to the trip), and in the Siberian Arctic in 2013.

Boss and Karp-Boss brought NASA to the project, earning a grant to collect biogeochemical information. They examined ocean color, composition and pigments of surface particles, including plankton, in relation to optical properties — light absorption, attenuation, fluorescence and backscattering. NASA uses the information to develop algorithms for, and verify data from, satellites that observe the same water.

Karp-Boss says she values meeting and working with international colleagues with expertise in other disciplines. The articles published May 22 are the result of the hard work of different teams and just scratch the surface of the rich data set, she says.

Boss says he appreciates Tara's emphasis on raising awareness about environmental issues and the opportunity he and other scientists have to interact with schoolchildren who board the vessel at each port.

Aboard Tara, an ecosystems biology approach is used. Researchers systematically sample the world's oceans across all domains of life, from viruses to animals, and collect a rich variety of environmental information.

Ocean plankton — microscopic beings that drift on the upper layer of the oceans — are as crucial to life on Earth as the rainforest ecosystem, say researchers. Ocean plankton produce half of the planet's oxygen, absorb and store carbon, influence the weather and are the base of the ocean food web that sustains the larger fish and marine mammals.

"Beyond the cutting-edge science that was developed thanks to our collaborative work with the Tara Expeditions Foundation, this adventure is also about showing people all over the world how important the ocean is for our own well-being," said Eric Karsenti, director of Tara Oceans, from the European Molecular Biology Laboratory (EMBL) and CNRS.

What's in the plankton?

Scientists captured viruses, microbes and microscopic eukaryotes — organisms with complex cells, from single-cell algae to fish larvae — from major oceanic regions and compiled the genetic material into comprehensive resources now available to the scientific community for additional study.

"This is the largest DNA sequencing effort ever done for ocean science: analyses 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.

EMBL's high-performance computing was essential in compiling the comprehensive catalog, estimated to be derived from more than 35,000 different species whose genomic content had previously been mostly unknown to scientists.

"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 CNRS. "They appear to be much more diverse than bacteria or animals, and most belong to little-known groups."

How do planktonic organisms interact?

Researchers used novel computer models to predict how diverse planktonic organisms interact. Predictions were confirmed via selective microscopy observations.

"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.

This map is a first step toward a better understanding of the dynamics and structure of the global marine ecosystem.

Are planktonic organisms distributed evenly in the oceans?

In addition, scientists studied how environmental factors — including temperature, pH, and nutrients — influence microscopic organisms floating in the ocean.

"We found that, at depths still reached by sunlight, temperature was the main factor that influences the composition of prokaryotes (bacteria and archaea) communities," said Peer Bork from EMBL. "Different sets of organisms come together depending on the water temperature."

Chase of UMaine conducted data analyses that supported scientists who showed the Agulhas "rings" — a natural barrier that draws the line between the Indian Ocean and the South Atlantic — separate plankton communities.

"It's like plankton goes through a cold wash cycle at the tip of South Africa," says Daniele Iudicone from Stazione Zoologica Anton Dohrn. "The current forms huge swirls that drastically mix and cool the plankton riding it, thus limiting the number of species that manage to cross."

Chase, from Canterbury, New Hampshire, was a UMaine graduate student during the 2013 Tara Oceans Polar Circle expedition. She says operating instruments below deck in the dry lab helped build her confidence as a researcher in the field.

"I like the international collaborative component," said Chase, who expects to earn her Ph.D. in oceanography in 2017. "We're all a part of something bigger and contributing to a broader understanding of the planet we live on and to the momentum and effort of sustaining our life here."

Matthew Sullivan from the University of Arizona said, "In addition, we now also have a global picture of marine virus communities, which allows us to confirm an idea that had been proposed a decade ago, but never proven. Viruses are produced in local 'seed banks' and then ride the ocean currents, so you end up with different cocktails of viruses in different places, even though the overall diversity of viruses in the oceans appears quite limited."

Understanding the distribution and interactions of the plankton across the oceans will be useful for predictive models necessary to study climate change, the scientists say.