Mesozooplankton dynamics in a glacially influenced Antarctic coastal system: insights from three years of image-based monitoring in Potter Cove

Antarctic coastal ecosystems are undergoing rapid transformations driven by warming, sea-ice loss, and glacial meltwater inputs, potentially altering zooplankton assemblages that play central roles in food webs. We present the first multi-year, full annual cycle (including winter) assessment of mesozooplankton in Potter Cove (King George/25 de Mayo Island) based on an automated image-based workflow (ZooImage). Samples were collected over 3 consecutive years (2012-2014) at 2 stations with contrasting meltwater influence and analyzed using complementary univariate and multivariate approaches. Multivariate analyses revealed significant but moderate seasonal variability in assemblage structure, without the formation of discrete seasonal clusters. Interannual differences were not significant, indicating relative structural stability across years. Community shifts were primarily driven by fluctuations in the relative abundance of dominant taxa, particularly cyclopoid and calanoid copepods and appendicularians, rather than by taxonomic turnover. Small-bodied taxa dominated numerically across seasons, whereas larger forms contributed disproportionately to biomass and exhibited stronger seasonal variability. Environmental variables explained a small but significant fraction of community variation, suggesting that hydrographic and trophic conditions modulate assemblage structure without fully determining it. Taxon-specific models further indicated differential responses across groups, reinforcing the view of gradual, quantitative shifts rather than abrupt community reorganization. ZooImage provided consistent abundance, biomass, and size-structured estimates, enabling standardized high-throughput processing and retrospective analysis of archived samples. Together, these findings establish an ecological and methodological baseline for long-term monitoring of glacially influenced Antarctic coastal ecosystems, highlighting seasonal forcing as the dominant driver of variability within an otherwise relatively stable interannual framework.