Five studies that were just published in the journal “Science” describe some results obtained by the international consortium Tara Oceans in an expedition accomplished between 2009 and 2013 around the oceans. A group of more than 200 people traveled on the 36-meter schooner Tara to collect more than 35,000 samples in the waters of the Earth’s seas to study even at the genetic level the presence of various types of plankton.

The term plankton is very generic because it includes a significant amount of very diverse marine organisms. Plankton can be divided into categories related to nutrition: phytoplankton, zooplankton and bacterioplankton. They can also be divided bt size with various categories ranging from the one that includes the viruses to the one that includes fish, cephalopods and other creatures visible to the naked eye.

Given the vast amount of plants, animals, viruses, bacteria, archaea, and even more creatures that are considered plankton, an expedition devoted to their study could only last for years. The research focused mainly on the layer of the upper ocean layer reached by sunlight, down to a 200 m depth, but some samples were collected at greater depths.

A genetic research of this magnitude was only possible thanks to modern DNA analysis techniques. The result was the cataloging of over forty million genes belonging to thousands of different species of living creatures. This study combined ecology, systems biology and oceanography to study plankton in their environment.

The genetic analysis allowed to create a plankton census but also to lay the foundation for a better understanding of the complexity of marine ecosystems. The research carried out are allowing to examine like never before the distribution of the various species in the seas and the relationships among them.

The Tara Oceans expedition uncovered many new species. A category that was still little known was that of the marine viruses as their study started only in the 1980s. Of the nearly 5,500 viral populations identified in the course of the expedition, only 39 were known previously.

Now it’s estimated that the amount of virus in the seas is ten times higher than that of the cellular life forms but there’s still a lot to be done to identify and understand their role in the ecosystems. For example, many viruses are bacteriophages and some researchers believe that they kill up to 40% of the existing bacteria in the oceans. Research such as the one carried out by Tara Oceans will allow to adjust these estimates.

The articles published in “Science” are just the beginning because there’s such a wealth of data that will allow many more analyzes. The Tara Oceans expedition scientists gave their colleagues those data so in the coming years we can expect further research based at least in part on them. They’ll allow us to better understand the oceans’ ecosystems, also relating to pollution and climate changes.