To explore the effects of variations in dissolved oxygen concentrations on the feeding and metabolism of the mussel Mytilus coruscus and analyze the relationship between shell opening behavior and respiratory metabolism, we observed and measured the shell valve opening degree and rates of filtration, oxygen consumption, and ammonia excretion of M. coruscus exposed to 8, 6, 4, 2, and 1 mg/L dissolved oxygen and calculated the O:N ratio. The results revealed the following: at oxygen concentrations greater than 4 mg/L, the shell valve of M. coruscus mainly remained opened but gradually closed when the oxygen concentration decreased to below 2 mg/L; when the oxygen concentration decreased to 4 mg/L, the filtration rate decreased significantly; and the oxygen consumption remained stable when the oxygen concentration was between 2 and 8 mg/L but declined significantly when the concentration decreased to 1 mg/L. The ammonia excretion rate showed an opposite tendency, increasing significantly when the oxygen concentration decreased to 2 mg/L, and the O:N ratio significantly decreased when the oxygen concentration decreased to 4 mg/L. Furthermore, a positive relationship was found between the shell valve opening degree and the rates of filtration and oxygen consumption. The findings of this study indicate that M. coruscus can adapt to fluctuations in dissolved oxygen concentrations within a certain range and maintain a relatively stable metabolic level. However, in environments where dissolved oxygen concentrations decrease to below 1 mg/L, these mussels are unable to maintain normal metabolism and respond to hypoxic stress by closing the shell valve to reduce energy consumption. These observations can provide a reference for investigating the hypoxia adaptive mechanism and farming of M. coruscus.