Zooplankton community structure and environmental drivers in the Indian sector of the Southern Ocean during the austral summer of 2022/2023

Abstract Poikilothermic and short-lived drifter species such as zooplankton are highly responsive to climate-driven changes and frontal systems in the Southern Ocean. To understand these changes, ongoing assessment of zooplankton is essential. Changes in abundance, biomass and species composition of zooplankton in the Indian sector of the Southern Ocean were assessed during the austral summer of 2022/2023 using a ring net that was towed obliquely from an average depth of 200 m to the surface. Thirty-six zooplankton taxa were identified at seven stations, with copepods constituting 64% of the population across 23 species. Zooplankton abundance and biomass were higher in Transect 2 (60–64°S) compared to Transect 1 (50–54°S). A cluster analysis revealed four zooplankton community groups. Notably, the distribution patterns of non-copepod taxa appeared to be influenced by diel vertical migration behaviour, which was closely tied to seasonal dynamics and the timing of sampling. This study improves our understanding of how different oceanographical fronts and behavioural patterns shape zooplankton communities in the Southern Ocean, emphasizing the need for improved sampling to include smaller zooplankton species and to better resolve temporal dynamics.