<p>Seasonal variation in phytoplankton composition influences the pathways and efficiency of energy flow, reshaping the structure of the trophic pyramid in the Ross Sea. However, field investigation of grazing processes presents challenges that hinder our understanding of energy pathways. This study aims to provide insights into energy flow using a three-dimensional ecosystem model applied to the Ross Sea. By analyzing the simulation results, the role of the seasonal phytoplankton succession, specifically the shift from dominance by <i>Phaeocystis antarctica</i> to diatoms, in energy allocation is explored. The short-lived spring bloom of <i>P. antarctica</i> mainly fuels microzooplankton, creating a brief food chain where energy transfers primarily among smaller plankton. In contrast, the subsequent summer bloom of diatoms, which persists longer, provides nearly half of the total phytoplankton energy loss (via ingestion and mortality) to larger mesozooplankton. Our findings indicate that phytoplankton succession in the Ross Sea extends the bloom duration, particularly for diatoms, thereby facilitating energy transfer to higher trophic levels and improving overall energy utilization. This suggests that phytoplankton succession, an ecological strategy adapted to iron-deficient environments in the Ross Sea, explains why the colder region in front of the Ross Ice Shelf is significantly more productive than the northern areas, ultimately favored by top predators.</p>