A data-driven assessment of the global community structure of pelagic zooplankton biomass

Corentin Clerc , Alexandre Schickele, Fabio Benedetti, Urs Hofmann Elizondo, Servane Lunven, Ruby Bader, Sébastien Vivier, Anthony J. Richardson, Meike Vogt

Aim: Zooplankton often dominate pelagic metazoan biomass, making them a central component of marine ecosystems and biogeochemical cycles. In this study, we aimed to: (1) provide biomass distributions of zooplankton functional types to support marine ecosystem monitoring and biogeochemical model evaluation; and (2) investigate regional and seasonal patterns of biomass across marine zooplankton functional types and their relationships with species diversity.

Location: Global.

Time Period: 1926-2016.

Major Taxa Studied: Marine zooplankton (ten plankton functional types, PFTs).

Methods: We compiled zooplankton biomass measurements from net samples and developed habitat suitability models to generate monthly global epipelagic (0-200~m) and mesopelagic (200-500 m) biomass climatologies for ten PFTs. We then linked epipelagic biomass climatologies to recent empirical species richness estimates to assess biomass-richness relationships at both community and PFT scales.

Results: Global epipelagic zooplankton biomass was estimated at 2.9 Pg C and exhibited strong seasonality, with summer maxima at high latitudes and persistently elevated biomass in productive regions. Mesopelagic biomass was lower (0.9 Pg C) and showed winter maxima at high latitudes. Crustaceans dominated global zooplankton biomass (>50% of total biomass), but gelatinous and calcifying zooplankton contributions were substantial (>10% each). At the community scale, the biomass-richness relationship was non-monotonic: both species-poor and species-rich environments had high biomass. At the PFT scale, crustacean biomass decreased with richness, whereas gelatinous zooplankton biomass increased.

Main conclusion:
Our analysis provides the first net-based monthly global biomass climatologies for ten zooplankton functional types across the epipelagic and mesopelagic zones. It shows that a few dominant crustacean groups capture much of the large-scale biomass structure but that resolving gelatinous taxa and calcifiers remains necessary because they contribute substantially to biomass and biogeochemical function. Together with the contrasting richness-biomass relationships among PFTs, these results indicate that biomass-based monitoring may be sufficient to track some crustacean-dominated patterns, whereas groups such as gelatinous zooplankton require metrics that also resolve diversity within PFTs.