Diurnal temperature variation exacerbates the effects of phenanthrene on Trochus pyramis Born in a warmer ocean.

Under global change scenarios, rising seawater temperature could affect the toxicity of chemical pollutants on marine organisms. Tropical species inhabiting coastal areas are especially vulnerable to diurnal temperature variation (DTV), yet the impacts of DTV on pollutant toxicity remains obscured. This study evaluated how a 4℃ DTV affects the toxicity of phenanthrene (PHE) on the physiological traits of Trochus pyramis, a key herbivorous gastropod in coral reef ecosystems, under both control (28°C) and elevated temperature (31°C) conditions. T. pyramis were exposed to PHE (1 and 10 μg/L) across different temperature scenarios for 14 days. Subsequently, PHE bioaccumulation, heat tolerance, antioxidant responses, and energy budgets of T. pyramis were assessed. The results showed that PHE had minimal effect on T. pyramis under DTV at 28°C, likely due to enhanced antioxidant responses and adaptive energy supply strategies induced by DTV. Conversely, DTV exacerbated the deleterious effect of PHE at 31°C, particularly under exposure to high-concentration PHE (10 μg/L), leading to reduced heat tolerance, suppressed antioxidant responses, and disturbed energy metabolism. These results underscore the necessity of incorporating DTV into PHE risk assessments for coral reef ecosystems in the context of global warming.