Zooplankton Contributions to Biogeochemical Carbon Cycling

Zooplankton, including copepods, krill and gelatinous predators, play pivotal roles in the ocean’s carbon cycle by mediating both passive and active transport of carbon from the surface to depth. Through their grazing on phytoplankton, excretion of faecal pellets and diel vertical migrations, these metazoans facilitate the conversion of dissolved and particulate organic matter into rapidly sinking particles that can be sequestered in the ocean interior for decades to centuries. The characteristics of faecal pellets—size, density and composition—determine sinking velocity and susceptibility to fragmentation or microbial remineralisation. In addition, flux‐feeding and suspension‐feeding behaviours influence the interception and repackaging of organic matter, modulating the efficiency of the biological carbon pump across different regions and depths. The interplay between zooplankton community structure, feeding modes and environmental factors such as mineral dust inputs, temperature and monsoon dynamics governs regional variability in carbon export. Collectively, these processes contribute significantly to global carbon sequestration, underlining the need to integrate detailed zooplankton behaviour into climate and biogeochemical models.

Research from Nature Portfolio

Recent studies have quantified the substantial carbon sequestration potential of pelagic macrozooplankton. In open‐ocean Antarctic ecosystems, krill produce fast‐sinking faecal pellets that alone sequester carbon at rates comparable to coastal blue carbon habitats, with billions of dollars’ worth of carbon stored for centuries. The sensitivity of krill populations to climate change and commercial fishing highlights critical conservation priorities to maintain this natural carbon sink. Parallel experiments simulating atmospheric dust deposition have shown that clay minerals interact with marine microorganisms to boost transparent exopolymer particle formation and form denser organoclay aggregates. These aggregates, once ingested by copepods, yield more rapidly sinking faecal pellets, thereby enhancing downward carbon flux and offering insights into dust‐driven enhancement of the biological carbon pump.

Zooplankton Contributions to Biogeochemical Carbon Cycling publication trend

The graph below shows the total number of articles in zooplankton contributions to biogeochemical carbon cycling across all publications each year (not limited to Nature Index journals).

Technical terms

Biological carbon pump: The suite of processes by which marine organisms convert dissolved CO2 into biomass and transport organic carbon from the surface to the deep ocean.

Faecal pellets: Aggregated excrement of zooplankton, rich in organic carbon and often rapidly sinking to depth.

Particulate organic carbon (POC): Organic matter particles, including phytoplankton, detritus and faecal pellets, suspended in the water column.

Diel vertical migration (DVM): Daily movement of zooplankton between surface waters at night to feed and deeper waters by day to avoid predation, promoting active carbon transport.

Transparent exopolymer particles (TEP): Gelatinous organic aggregates formed by microbial exudates that facilitate the flocculation and sinking of organic matter.

References

1. Antarctic krill sequester similar amounts of carbon to key coastal blue carbon habitats. Nature Communications (2024).
2. Organoclay flocculation as a pathway to export carbon from the sea surface. Scientific Reports (2024).
3. Sinking fate and carbon export of zooplankton fecal pellets: insights from time-series sediment trap observations in the northern South China Sea. Biogeosciences (2023).
4. The Roles of Suspension-Feeding and Flux-Feeding Zooplankton as Gatekeepers of Particle Flux Into the Mesopelagic Ocean in the Northeast Pacific. Frontiers in Marine Science (2019).
5. Zooplankton-Mediated Fluxes in the Eastern Tropical North Atlantic. Frontiers in Marine Science (2020).