The Ross Sea is one of the most productive regions of Antarctica and a key hotspot for Southern Ocean biogeochemical cycling. In this area, the Ross Ice Shelf (RIS) exerts a major influence on the physical and biogeochemical properties of the water column, releasing large amounts of freshwater during summer. However, the consequences of these meltwater inputs on primary production processes remain poorly understood. Phytoplankton communities respond rapidly to environmental stressors through shifts in biomass and functional traits, with cascading effects on trophic transfer efficiency, carbon export, and ecosystem functioning.This study investigates how meltwater‑driven gradients shape phytoplankton community structure along a west–east transect between Ross Island and Cape Colbeck during the Austral Summer 2025, within the framework of the GLOB project (40th Italian Antarctic Expedition).Preliminary results reveal a pronounced west‑to‑east gradient associated with increasing freshwater influence. Although microphytoplankton dominated total biomass across the transect, stations affected by meltwater showed a progressive shift toward smaller size classes, with rising contributions of nano‑ and picophytoplankton. Pigment analyses indicated elevated chlorophyll‑b concentrations along the freshwater gradient, pointing to an increasing presence of chlorophyll‑b‑containing taxa. Molecular data supported these patterns, confirming a diatom‑dominated assemblage throughout the transect but with a growing relative contribution of Chlorophyta and other non‑diatom groups in the eastern, meltwater‑influenced stations.These findings suggest that meltwater inputs linked to RIS dynamics act as key ecological drivers structuring phytoplankton communities. Even subtle shifts toward smaller size classes may alter trophic pathways, reducing energy transfer efficiency to higher consumers and modifying carbon export dynamics. Under future scenarios of intensified ice‑shelf melting, such changes could significantly reshape biodiversity patterns and ecosystem functioning in Antarctic coastal environments.