How the Mediterranean mussel Mytilus galloprovincialis responds to multiple environmental challenges: Vibrio splendidus and hydrocarbon mixture.

Marine organisms are exposed to a wide range of environmental stressors and must develop adaptive responses to survive. This study investigated how Mytilus galloprovincialis responds to chemical and biological stress, both separately and simultaneously. Mussels were exposed for 4 days to a hydrocarbon mixture (diesel + oil engine) and then injected with Vibrio splendidus. Six hours post-injection, responses were assessed by measuring phagocytosis, several immune-related enzymes (lysozyme, phenoloxidase, glutathione peroxidase) and chaperonins (HSP70, HSC70) activities. The contact with the pathogen enhanced phagocytic activity, whereas hydrocarbon mixture inhibited it, confirming hemocytes' sensitivity to environmental stress. Immune-related enzymes measured in plasma, adductor muscle, and digestive gland modulated their activity with particular emphasis on mussels subjected to multiple stress, indicating their involvement in maintaining homeostasis under stressful environmental conditions. Furthermore, chaperonins showed significantly higher values after all treatments. In conclusion, both the pathogen challenge and the hydrocarbon mixture (separately and simultaneously) influenced the parameters considered in the different tissues, suggesting their potential additive effect on M. galloprovincialis. These findings can confirm the importance of M. galloprovincialis as a valuable bioindicator for studying adaptive mechanisms to multiple stressors and assessing marine environmental health.