Physiological responses of Mediterranean octocorals to prolonged exposure to ecologically relevant microplastic concentrations

Microplastics (MPs) are pervasive contaminants in the Mediterranean Sea, yet their long-term effects on habitat-forming octocorals remain poorly understood. Here, we experimentally evaluated the physiological responses of the gorgonians Eunicella singularis and Paramuricea clavata after three months of exposure to a mixture of PET, PS, and PP particles. Respiration, feeding performance, organic matter content, MP ingestion and histological condition were assessed at the end of the experiment. MP exposure significantly reduced respiration rates in both species, indicating metabolic depression and potential energy-conservation responses, while prey capture and organic matter content remained stable. Both gorgonians ingested MPs, dominated by PET, with species-specific differences in particle number and size retention. No tissue damage or structural alterations were detected, suggesting effective clearance rather than long-term retention. Overall, prolonged exposure produced limited physiological impairment, although metabolic adjustments may represent sublethal energetic trade-offs with implications for long-term resilience under future stress scenarios.