Effects of elevated temperatures on oxidative stress, antioxidant and biochemical responses in the azooxanthellate coral Tubastraea aurea

Abstract

Introduction Coral reefs are highly productive marine ecosystems that support biodiversity, nutrient cycling, and coastal protection. Thermal stress associated with ocean warming threatens coral physiology by disrupting metabolism, antioxidant defenses, and tissue integrity. Tubastraea aurea, a stony coral with fleshy polyps and a calcareous skeleton, was investigated to determine how increasing temperature affects biochemical composition, oxidative stress responses, and morphological condition under controlled laboratory conditions.Methods Coral colonies were exposed to three temperature regimes, 21 degrees C, 25 degrees C, and 29 degrees C, to evaluate thermal stress effects. Biochemical parameters, including protein and glucose concentrations, were analyzed together with antioxidant biomarkers such as superoxide dismutase, catalase, glutathione S-transferase, and lipid peroxidation. Morphological observations were also conducted to assess tissue coverage, skeletal appearance, and overall physiological condition.Results Protein and glucose levels showed moderate alterations across temperature treatments, although statistical significance was not detected. Reductions were limited at 25 degrees C but became pronounced at 29 degrees C, suggesting disruption of protein synthesis and carbohydrate metabolism. Corals maintained at 21 degrees C and 25 degrees C retained healthy tissue coverage, whereas specimens exposed to 29 degrees C displayed darkened skeletal walls and restricted living tissue, indicating severe physiological damage. Antioxidant enzyme activities changed significantly under thermal stress. Superoxide dismutase activity increased progressively with temperature, reflecting enhanced reactive oxygen species production. Catalase activity rose at 21 degrees C and 25 degrees C, indicating adaptive detoxification responses. Lipid peroxidation levels increased under all temperature conditions, demonstrating oxidative membrane damage. Glutathione S-transferase activity also increased with temperature, confirming activation of cellular detoxification pathways.Discussion The findings demonstrate that sustained warming negatively affects the stability, antioxidant balance, and morphology of T. aurea. Elevated temperature redirected metabolic energy toward stress defense mechanisms instead of growth, tissue maintenance, and skeletal development. Increased antioxidant enzyme activities and lipid peroxidation confirmed the occurrence of oxidative stress and cellular damage under high temperature exposure. The severe tissue degradation observed at 29 degrees C suggests reduced coral resilience and highlights the potential consequences of ocean warming for coral survival, function, and persistence.