In situ imaging reveals the biomass of giant protists in the global ocean.
Planktonic organisms play crucial roles in oceanic food webs and global biogeochemical cycles. Most of our knowledge about the ecological impact of large zooplankton stems from research on abundant and robust crustaceans, and in particular copepods. A number of the other organisms that comprise planktonic communities are fragile, and therefore hard to sample and quantify, meaning that their abundances and effects on oceanic ecosystems are poorly understood. Here, using data from a worldwide in situ imaging survey of plankton larger than 600 μm, we show that a substantial part of the biomass of this size fraction consists of giant protists belonging to the Rhizaria, a super-group of mostly fragile unicellular marine organisms that includes the taxa Phaeodaria and Radiolaria (for example, orders Collodaria and Acantharia). Globally, we estimate that rhizarians in the top 200 m of world oceans represent a standing stock of 0.089 Pg carbon, equivalent to 5.2% of the total oceanic biota carbon reservoir. In the vast oligotrophic intertropical open oceans, rhizarian biomass is estimated to be equivalent to that of all other mesozooplankton (plankton in the size range 0.2-20 mm). The photosymbiotic association of many rhizarians with microalgae may be an important factor in explaining their distribution. The previously overlooked importance of these giant protists across the widest ecosystem on the planet changes our understanding of marine planktonic ecosystems.
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire Adaptation et Diversité en Milieu Marin UMR7144, Station Biologique de Roscoff, 29688 Roscoff, France.|Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV) UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France.
Tristan
T
Biard
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV) UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France.
Lars
L
Stemmann
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV) UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France.
Marc
M
Picheral
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV) UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France.
Nicolas
N
Mayot
GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany.
Pieter
P
Vandromme
GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany.
Helena
H
Hauss
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV) UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France.
Gabriel
G
Gorsky
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire d'Océanographie de Villefranche (LOV) UMR7093, Observatoire Océanologique, 06230 Villefranche-sur-Mer, France.
Lionel
L
Guidi
GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany.
Rainer
R
Kiko
Sorbonne Universités, UPMC Université Paris 06, CNRS, Laboratoire Adaptation et Diversité en Milieu Marin UMR7144, Station Biologique de Roscoff, 29688 Roscoff, France.
Fabrice
F
Not
D000818:Animals; D018533:Biomass; D058448:Biota; D002244:Carbon / Q000378:metabolism; D057965:Carbon Sequestration; D018534:Earth, Planet; D058086:Microalgae / Q000378:metabolism; D009792:Oceans and Seas; D010788:Photosynthesis; D056901:Rhizaria / Q000145:classification / Q000302:isolation & purification* / Q000378:metabolism; D012623:Seawater / Q000737:chemistry; D013559:Symbiosis; D015048:Zooplankton / Q000145:classification / Q000302:isolation & purification* / Q000378:metabolism
D002244:Carbon