Microzooplankton Grazing Dynamics in Marine Ecosystems

Microzooplankton—heterotrophic protists such as ciliates and small dinoflagellates—mediate the transfer of primary production through direct grazing on phytoplankton and bacteria. By consuming a substantial fraction of daily primary production, they control phytoplankton standing stock, drive nutrient regeneration and shape carbon export to higher trophic levels or into the deep ocean. Rates of microzooplankton grazing vary spatially and seasonally, responding to changes in temperature, nutrient availability and phytoplankton size‐structure. Techniques such as dilution experiments and mesocosm studies have quantified grazing mortality, revealing that small prey often experience higher turnover in oligotrophic waters, while larger blooms can enhance trophic transfer efficiency. These dynamics underpin global biogeochemical cycles and inform ecosystem models, especially as climate change alters ocean stratification, bloom phenology and food‐web topology.

Research from Nature Portfolio

Recent studies have shown that the fate of organic carbon during large phytoplankton blooms is strongly influenced by viral infection of hosts, which can shift the balance between bacterial and eukaryotic recyclers. When high viral pressure terminates a bloom, thraustochytrid biomass rivals that of bacteria, increasing rates of extracellular carbon release in forms that enhance deep‐ocean export. In a foundational ocean transect study, microzooplankton in oligotrophic regions consumed nearly 80% of primary production, compared with around 66% in more productive zones, demonstrating marked differences in grazing pressure, diel feeding rhythms and energy transfer efficiency along productivity gradients. Together these findings underscore the variability of microzooplankton herbivory and its central role in carbon cycling under differing oceanographic contexts.

Microzooplankton Grazing Dynamics in Marine Ecosystems publication trend

The graph below shows the total number of articles in microzooplankton grazing dynamics in marine ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Microzooplankton: Heterotrophic unicellular protists (ciliates, small dinoflagellates) that graze on phytoplankton and bacteria.

Grazing rate: The proportion of prey biomass consumed per unit time, often expressed as d⁻¹.

Dilution experiment: A method to estimate microzooplankton grazing by diluting seawater with filtered water and measuring prey growth and loss rates.

Trophic transfer efficiency: The fraction of primary production passed from one trophic level to the next.

Oligotrophic: Nutrient-poor waters with low primary productivity, often dominated by small phytoplankton and efficient microbial recycling.

References

1. Viral infection switches the balance between bacterial and eukaryotic recyclers of organic matter during coccolithophore blooms. Nature Communications (2023).
2. Coexisting picoplankton experience different relative grazing pressures across an ocean productivity gradient. Proceedings of the National Academy of Sciences of the United States of America (2023).
3. Changes in phytoplankton size–structure alter trophic transfer in a temperate, coastal planktonic food web. Limnology and Oceanography Letters (2024).
4. Planktonic food web structure and trophic transfer efficiency along a productivity gradient in the tropical and subtropical Atlantic Ocean. Scientific Reports (2019).