The Tara Oceans data reveal a universal trend in geographical distribution of rare planktonic species

© Tara Expeditions Foundation

Based on the large number of plankton samples collected aboard the schooner Tara during her 4-year expedition on all the world’s oceans, researchers at the Institute of Biology of Ecole Normale Supérieure, in collaboration with the Tara Oceans consortium, have shown a pattern common to all plankton communities worldwide.

The abundance of each species within a community is linked to its ecological role. The most abundant species are the most successful in local competition. Alongside these “winners”, microbial ecosystems – plankton in particular – are also home to a huge number of species of low abundance, whose origin and function remain mysterious. They compose the “rare biosphere”.

Using metabarcoding , researchers were able to assess global abundances of unicellular eukaryotes present on the ocean surface, comparing data from samples collected on 121 sites.

They have shown that, despite a large geographic variability in composition, the rare biosphere seems to obey common principles. The decrease in abundance of 99% of the least abundant species follows the same power-law trend. The exponent associated to this decrease can be quantified with an error of less than 10%, that is to say with a higher precision than most of known ecological patterns.

carte tara ocean plancton article science actu

This surprising regularity, this signature common to all the world’s oceans, suggests the existence of shared and global processes governing the “rare biosphere” ecology. The Tara Oceans researchers also hypothesize that this part of the community does not respond to the local environmental context, but depends on phenomena of large geographical extent, such as the mixing induced by global ocean circulation, allowing the various species to integrate – in time and space – fluctuations in the marine environment.

This work provides a new perspective oni the functioning and ecology of non-dominant plankton species, which are considered major players within marine plankton ecosystems.

[1] Metabarcoding: DNA sequencing technique applied to part of the cells in a sample to characterize the species present.

Related articles