Morphological and taxonomic diversity of mesozooplankton is an important driver of carbon export fluxes in the ocean

Abstract

Mesozooplankton is a very diverse group of small animals ranging in size from 0.2 to 20 mm not able to swim against ocean currents. It is a key component of pelagic ecosystems through its roles in the trophic networks and the biological carbon pump. Traditionally studied through microscopes, recent methods have been however developed to rapidly acquire large amounts of data (morphological, molecular) at the individual scale, making it possible to study mesozooplankton using a trait‐based approach. Here, combining quantitative imaging with metabarcoding time‐series data obtained in the Sargasso Sea at the Bermuda Atlantic Time‐series Study (BATS) site, we showed that organisms' transparency might be an important trait to also consider regarding mesozooplankton impact on carbon export, contrary to the common assumption that just size is the master trait directing most mesozooplankton‐linked processes. Three distinct communities were defined based on taxonomic composition, and succeeded one another throughout the study period, with changing levels of transparency among the community. A co‐occurrences' network was built from metabarcoding data revealing six groups of taxa. These were related to changes in the functioning of the ecosystem and/or in the community's morphology. The importance of Diel Vertical Migration at BATS was confirmed by the existence of a group made of taxa known to be strong migrators. Finally, we assessed if metabarcoding can provide a quantitative approach to biomass and/or abundance of certain taxa. Knowing more about mesozooplankton diversity and its impact on ecosystem functioning would allow to better represent them in biogeochemical models.

Relationships Between Plankton Size Spectra, Net Primary Production, and the Biological Carbon Pump

“…However, we did not find a statistically significant correlation between export efficiency and the NBSS slope (although the non-significant correlation was positive, as predicted, Figure 6b). Our results also align with a recent study from the Sargasso Sea showing that zooplankton size did not correlate with export flux (Perhirin et al, 2024). That study also showed that opacity was an important zooplankton trait that correlated strongly with export flux, and although we could not quantify opacity from our dataset, several of our highest export efficiency locations (from the SalpPOOP cruise, Décima et al, 2023) were measured within a bloom of highly transparent pelagic tunicates.…”