The Tara sailing through ice chunks --taken using the Tara drone. Credit: Francois Aurat_Foundation Tara Ocean

Two ocean studies look at microscopic diversity and activity across entire planet

In an effort to reverse the decline in the health of the world's oceans, the United Nations (UN) has declared 2021 to 2030 to be the Decade of Ocean Science for Sustainable Development.

One key requirement for the scientific initiative is data on existing global ocean conditions. An important trove of data is already available thanks to the Tara Oceans expedition, an international, interdisciplinary enterprise that collected 35,000 samples from all the world's oceans between 2009 and 2013. The samples were collected by researchers aboard one schooner, the Tara, at depths ranging from the surface to 1,000 meters deep.

Two papers being published November 14 in the journal Cellare the latest to use samples and data collected during the Tara Oceans expedition to analyze diversity across the entire planet of plankton, microscopic organisms that drift on oceanic currents that are key for the well-being of our oceans. One study focused on the diversity of plankton across Earth's oceans, whereas the other study assessed gene expression among microbial communities as a way to predict how these communities might adapt to changing environmental conditions.

Plankton Diversity across Different Latitudes

"Everything in the ocean is connected, which means it has the potential to move around," says Chris Bowler, a National Center for Scientific Research (CNRS) scientist at the Institut de Biologie de l'Ecole Normale Superieure (IBENS) in Paris and a co-senior author of the plankton study. "This makes it important to assemble everything on a global scale. Doing deep analysis also allows us to catch the rare organisms in the biosphere in addition to those that are more abundant."

"Our study focused on plankton because it's a major contributor to marine ecosystems in terms of biomass, abundance, and diversity," says co-senior author Lucie Zinger of IBENS. "All types of life have representatives in the plankton—bacteria, archaea, protists, animals and plants, as well as viruses. But the large majority of this diversity is invisible to the naked eye."

Two ocean studies look at microscopic diversity and activity across entire planet
A general view from the mass of the Tara as it sails through ice chunks. Credit: Francois Aurat_Foundation Tara Ocean

The paper reports that the large majority of planktonic groups, from giant viruses to small animals, follow a gradient of diversity along latitudes, with the lowest level of diversity closest to the poles. "Ocean temperature is mainly responsible for this pattern," Zinger notes. "Ocean warming due to climate changeis likely to lead to a 'tropicalization,' or increase, of plankton diversity in temperate and polar waters. The consequences of this are still unclear, but we know these geographic areas are currently very important for different ecosystem services, including fisheries and carbon sequestration."

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More information: Cell, Ibarbalz et al.: "Global Trends in Marine Plankton Diversity across Kingdoms of Life" DOI: 10.1016/j.cell.2019.10.008

Cell, Salazar et al.: "Gene Expression Changes and Community Turnover Differentially Shape the Global Ocean Metatranscriptome" DOI: 10.1016/j.cell.2019.10.014

One Earth, Claudet et al.: "A Roadmap for Using the UN Decade of Ocean Science for Sustainable Development in Support of Science, Policy, and Action" DOI: 10.1016/j.oneear.2019.10.012

Journal information: Cell