The spatial distribution of phytoplankton in Gamak Bay in Fall, 2021 was characterized by nutritional modes. While physiochemical parameters were measured, phytoplankton community was analyzed using a light microscope for microplankton and flow cytometry for picoplankton. Principal component analysis (PCA), correlation analysis (CA), and regression analysis were performed to assess the correlation of major phytoplankton groups with dissolved inorganic nutrients for autotrophs and prey for mixo/heterotrophic protists. Diatoms were most abundant at Yeosu Harbor and statistical analysis showed that diatoms were most correlated with phosphate. In Inner Bay, dinoflagellates were abundant and largely associated with autotrophic bacteria. This study highlights that nutritional strategies can govern the distribution of major phytoplankton groups in Gamak Bay in the fall.