Summer mortality impacts the productivity of greenlip abalone, Haliotis laevigata, on land-based farms in South Australia. It is associated with high water temperature (greater than 23°C), low dissolved oxygen levels, increased bacterial loads, and immune system suppression during summer months. This study aimed to alleviate mortality rates of greenlip abalone by dietary intervention using vitamin K₁ to support the innate immune system and oxidative status. Dietary vitamin K₁ at 0.0, 0.5, 1.0, and 5.0 mg kg^-1 was added to a commercially formulated diet mash. An additional diet containing 0.5 mg kg^-1 of K₃ was also used for comparison. Diets were fed to 3-y-old abalone (71.51 g; 79.91 mm) at 22 and 25°C water temperatures for 39 days. No mortalities were observed at 22°C; however, high mortalities were observed in all dietary treatments at the water temperature of 25°C. Compared with the negative control diet (0.0 mg additional inclusion ofK₁ or K₃ kg^-1) at 25°C, the inclusion of vitaminK₁ orK₃ did not improve survival of greenlip abalone (P > 0.05). VitaminK₁ inclusion level resulted in significant increases in vitamin K₁ concentration of visceral organ and muscle tissues (P < 0.05). Steady-state levels of vitamin K₁ were not reached. Steady-state levels of K₂-MK-4 in visceral organ and muscle were reached when analyzed levels of dietary vitamin K₁ reached 0.02 mg kg^-1. This was also true for K₂-MK-7, but in the visceral organ only. Vitamin K₁ inclusion level did not significantly affect total hemocyte count, phagocytic activity, or phagocytic index (P > 0.05). Increasing water temperature to 25°C resulted in significant increases in serum catalase activity (22 < 25°C) and vitaminK₁ concentration in muscle tissue (22 < 25°C). Comparison of vitamin K₁ or K₃ at 0.5 mg kg^-1 resulted in significant changes to serum catalase activity (K₁ > K₃) and vitamin K₁ concentration in visceral organ (K₁ >K₃). In conclusion, vitaminK₁ at the doses tested, resulted in significant increases in vitaminK₁ concentration in visceral organ and muscle tissues, but failed to improve immune function, oxidative status, or survival of greenlip abalone at high summer water temperatures.