Oxidative and metabolic responses in Crassostrea gasar under combined stressors of elevated temperature and microplastic exposure

This study investigates two critical threats to species such as the oyster Crassostrea gasar: elevated temperatures and microplastic (MP) contamination. To assess the combined effects of MP and temperature, oysters were exposed to different temperatures (20 °C, 26 °C, and 28 °C, with 20 °C considered the control group) and to a nominal concentration of 100 μg/L of MP (spherical polystyrene, 1.1 μm) at the same temperatures for 7 days. Oxidative stress parameters were analyzed, including the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), as well as glutathione (GSH) levels and lipid peroxidation. Additionally, energy metabolism indicators, such as glucose and lactate levels and lactate dehydrogenase activity, were evaluated, along with the accumulation of MP in the gills and digestive glands of oysters. The results showed that regardless of temperature both gills and digestive gland accumulated MP. Besides, the thermal stress increased GST activity in both tissues and altered GSH levels. At the highest temperature, MP exposure led to increased SOD activity in the gills and decreased CAT activity in the digestive gland. GST activity was elevated in oysters exposed to MP at 20 °C, alongside higher GSH levels. At 26 °C, glucose and lactate levels, as well as lactate dehydrogenase activity, were significantly elevated. Co-exposure to MP notably affected oysters at 26 °C, reducing glucose levels in the gills while increasing them in the digestive gland. The Integrated Biomarker Response (IBR) index revealed that co-exposure had a more pronounced impact on the gills than on the digestive gland. Overall, this study underscores how a commercially important oyster species could be adversely affected by the combined impacts of global warming and MP contamination.