Global abundance of planktonic heterotrophic protists in the deep ocean

Massimo C. Pernice*, Irene Forn, Ana Gomes, Elena Lara, Laura Alonso-Sáez, Jesus M. Arrieta, Francisca Del Carmen Garcia, Victor Hernando-Morales, Roy Mackenzie, Mireia Mestre, Eva Sintes, Eva Teira, Joaquin Valencia, Marta M. Varela, Dolors Vaqué, Carlos M. Duarte, Josep M. Gasol, Ramon Massana

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


The dark ocean is one of the largest biomes on Earth, with critical roles in organic matter remineralization and global carbon sequestration. Despite its recognized importance, little is known about some key microbial players, such as the community of heterotrophic protists (HP), which are likely the main consumers of prokaryotic biomass. To investigate this microbial component at a global scale, we determined their abundance and biomass in deepwater column samples from the Malaspina 2010 circumnavigation using a combination of epifluorescence microscopy and flow cytometry. HP were ubiquitously found at all depths investigated down to 4000 m. HP abundances decreased with depth, from an average of 72±19 cells ml-1 in mesopelagic waters down to 11±1 cells ml-1 in bathypelagic waters, whereas their total biomass decreased from 280±46 to 50±14 pg C ml-1. The parameters that better explained the variance of HP abundance were depth and prokaryote abundance, and to lesser extent oxygen concentration. The generally good correlation with prokaryotic abundance suggested active grazing of HP on prokaryotes. On a finer scale, the prokaryote:HP abundance ratio varied at a regional scale, and sites with the highest ratios exhibited a larger contribution of fungi molecular signal. Our study is a step forward towards determining the relationship between HP and their environment, unveiling their importance as players in the dark ocean's microbial food web.

Original languageEnglish (US)
Pages (from-to)782-792
Number of pages11
JournalISME Journal
Issue number3
StatePublished - Mar 25 2015

Bibliographical note

Publisher Copyright:
© 2015 International Society for Microbial Ecology All rights reserved.

ASJC Scopus subject areas

  • Microbiology
  • Ecology, Evolution, Behavior and Systematics


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