Abstract

Artificial illumination generated during deep-sea mining may impose physiological disturbances on mesopelagic fishes that have long adapted to extremely dim environments, however, the quantitative relationship between light stress intensity/duration and biological responses remains unclear. In this study, Epinephelus lanceolatus was used as a model species to investigate transcriptomic changes in eye and brain tissues under no light (0 lx), weak light (900 lx), and strong light (2000 lx) conditions, aiming to define the biological thresholds of light-induced effects. The results revealed that the eye was highly sensitive to light exposure, with weak light significantly upregulating genes related to visual signal transduction and energy metabolism, whereas the brain exhibited fewer transcriptional changes and maintained homeostasis, showing a differentiated response pattern of “active eye-stable brain”. Short-term exposure (24 h) primarily induced acute stress and rapid metabolic adjustments, while long-term strong-light exposure (72 h) led to circadian rhythm disruption, mitochondrial dysfunction, and persistent metabolic burden, potentially impairing growth and reproduction. Based on these mechanistic insights, we propose a dual-threshold model of “adaptive threshold-stress threshold”: ≤10 3  lx as a low-risk level and ≥ 10 3  lx as a high-risk level. Accordingly, it is recommended that deep-sea mining operations restrict illumination within the weak-light range (≤10 3  lx), avoid prolonged continuous exposure, and adopt intermittent, directional, and tiered lighting strategies. Incorporating light intensity, duration, and frequency into environmental risk assessments, alongside noise and sediment plume impacts, will support integrated risk management and help mitigate ecological impacts on mesopelagic nekton.