The sublethal toxicity of water-accommodated fractions of bunker oil was tested on Kappaphycus sp., revealing that lower oil concentrations (0.1, 1, and 10 ppm) increased photosynthesis rates after 24 hours, with 1 ppm showing a significantly higher rate than the control. Respiration rates also rose with oil concentration increases, with notable effects at 1000 ppm, but chlorophyll a content changes were statistically insignificant. Despite increases in photosynthesis and respiration under certain conditions, the findings suggest that Kappaphycus sp. can be resilient to oil spills, with low bioconcentration factors indicating they remain safe for human consumption even in oil-affected waters.