Key link between iron and the size structure of three major mesoplanktonic groups in the upper ocean
- Mathilde Dugenne
- Marco Corrales-Ugalde
- Jessica Y. Luo
- Lars Stemmann
- Jean-Olivier Irisson
- Fabien Lombard
- Todd O’Brien
- Charles Stock
- Marc Picheral
- Lionel Guidi
- Andrew M. P. McDonnell
- Laetitia Drago
- Zoé Mériguet
- Marion Vilain
- Chloé Tilliette
- Nagib Bhairy
- Sophie Bonnet
- Thelma Panaïotis
- Margaux Noyon
- Cécile Guieu
- Astrid Cornils
- Jean-Baptiste Romagnan
- Nina Grandrémy
- François Carlotti
- Magali Lescot
- Emilie Riquier
- Laetitia Jalabert
- Amanda Elineau
- Corinne Desnos
- Helena Hauss
- Jan Taucher
- Barbara Niehoff
- Jenny Huggett
- Rainer Kiko
2026-07-14
In marine ecosystems, critical services like fish production, carbon export, or the delivery of nutrients through N 2 -fixation rely heavily on the size spectrum of pelagic organisms, particularly mesoplankton (200-20,000 µ m). However, the linkages between environmental factors and mesoplankton spectral biogeography remain largely unresolved, as so far only limited datasets exist to understand the large-scale shifts in mesoplankton size. Using global compilations of Rhizarian, colonial N 2 -fixer, and Crustacean images, we reveal the role of iron in shaping the size structure and related biogeography of these groups. Our findings underscore the importance of atmospheric sources of iron for N 2 -fixers and Rhizarians while total iron, accounting for organic and inorganic compounds, appeared to explain a high percentage of the variance in Crustacean size structure via apparent recycling. Using environmental explanatory variables, our models reached high R 2 (0.93, 0.88, and 0.79 respectively), providing robust predictions of mesoplankton size structure related to elemental cycling and ecosystem services. Our results suggest that without compensatory mechanisms, future increases in global temperatures could have negative effects on mesoplankton size, possibly limiting carbon export from the productive layers to sequestration depth, that might be offset by expected increases in iron inputs that benefit N 2 -fixers, Rhizarians, and eventually Crustaceans.