Physiological responses of the cold-water octocoral Dentomuricea aff. meteor to sublethal effects of Cu exposure: A risk assessment to deep-sea mining activities

The growing commercial demand for metal resources has increased interest in deep-sea mining, raising concerns about the environmental impacts on benthic organisms from metals such as copper (Cu) released during excavation and dewatering processes. Previous research found that the cold-water octocoral Dentomuricea aff. meteor has a lethal Cu concentration (LC50) of 137 μg L^-1, indicating its high sensitivity to Cu. This study investigates the response of the cold-water octocoral D. aff. meteor to sublethal Cu concentrations (5-60 μg L^-1) over a two-week exposure period followed by a two-week recovery phase. Results show that Cu accumulates in both coral tissue and skeleton, with concentrations reaching up to 39 μg g^-1 in tissue and 38 μg g^-1 in skeleton at the highest exposure level. Despite initially maintaining cellular homeostasis, the corals exhibited persistent oxidative stress during recovery, evidenced by elevated levels of lipid peroxidation (MDA), stress signalling (HSP70) and antioxidant biomarkers (CAT, GPx and SOD). This research provides critical insights into how cold-water corals respond to and recover from Cu exposure, emphasizing their vulnerability under mining scenarios. The findings underscore the necessity of regular monitoring of deep-sea mining sites, as delayed toxicity responses could threaten these ecosystems. The study highlights the importance of incorporating such data into industry guidelines and International Seabed Authority (ISA) regulations to balance environmental protection with economic interests. Effective management and periodic reassessment of mining impacts are essential to protect these sensitive deep-sea organisms.