Different amino acid compositions and food quality of particulate organic matter driven by two major phytoplankton groups in the Ross Sea

Understanding the amino acid (AA) composition of phytoplankton-derived particulate organic matter (POM) is crucial for unraveling phytoplankton physiology and assessing food quality. This study investigated AA compositions and food quality of POM associated with two phytoplankton groups in the Ross Sea polynya. The Phaeocystis antarctica (P. antarctica)-predominant group, with P. antarctica overwhelmingly contributing to its composition, demonstrated a fresh state and heightened physiological activity. In contrast, the P. antarctica and diatoms-mixed group exhibited superior essential amino acids (EAAs) contributions and a higher EAA index (EAAI), indicating enhanced food quality. Dissimilarity Index values provided nuanced insights into degradation stages not captured by other indices. Despite lower physiological activity, diatoms in the mixed group stood out as crucial sources of high-quality nutrition for higher trophic levels in the Ross Sea polynya. The observed variations in AA compositions not only reflected the phytoplankton community structure but also provided insights into their physiological conditions. Given the ongoing climate-induced environmental changes potentially influencing phytoplankton communities, this study underscores the potential impacts on the intricate food web dynamics in the Ross Sea polynya. The assessment of AA composition emerged as a valuable tool for understanding the ecological implications for higher trophic levels in this polar region.