SENTINEL SPECIES AND ECOSYSTEM HEALTH: AN INTEGRATED APPROACH TO UNVEILING THE IMPACT OF MARINE POLLUTION

The release of hydrocarbons from human activities is threatening the marine environment, causing impacts of varying degrees that can alter the balance of entire ecosystems and modify their biodiversity levels. This issue is receiving attention, especially given the recent increase in the release of these substances in the Mediterranean Sea. To evaluate how these compounds can alter the immune activity of animals, several experiments were conducted under controlled laboratory conditions using the well-known sentinel organism Mytilus galloprovincialis. Immune responses were investigated using various techniques, ranging from immunological to physiological analyses. Exposure to different concentrations of hydrocarbon mixture (HC) resulted in a significant decrease in the phagocytic activity, as well as modulation of several immune-related enzymes activity (lysozyme, phenoloxidase, glutathione peroxidase, alkaline phosphatase, and esterase). Alterations in normal tubular structure and stimulation of HSP70 and HSC70 were detected especially after exposure to the highest concentration. Moreover, a shift in hemolymph and digestive gland microbial community was observed, with an increase in the relative abundance of obligate hydrocarbon-degrading bacteria (Alcanivorax, Oleibacter), suggesting their role in maintaining homeostasis. The involvement of several immune-related enzymes (i.e. lysozyme, phenoloxidase, and glutathione peroxidase) was also observed after multiple stress (HC exposure and Vibrio splendidus challenge). HSP70 and HSC70 also increased their activity after the combined treatment, as well as the metabolites level belonging to osmotic, defence and energy pathways measured in posterior adductor muscle and digestive gland. Interestingly, mussels’ capability to recovery after 4 days of HC exposure was measured at different time point in clean seawater (i.e. 0, 3, 7, 14, 30 days). Phagocytosis activity, % of cells with DNA fragmentation partially recovered after about 7 and 3 days respectively. The activity of several immuno-related enzymes (lysozyme, glutathione peroxidase, esterase and alkaline phosphatase) measured in plasma, gills and digestive gland showed a different time to recovery, highlighting their involvement within the recovery dynamics. Moreover, changes in the relative abundance of microbial communities in hemolymph and digestive gland during recovery also suggest an adaptive mechanism aimed at restoring homeostasis. Indeed, while the hemolymph showed high abundance of hydrocarbon-degrading taxa, digestive gland showed high abundance of polysaccharide-degrading and antioxidant-producing taxa. This approach, which involves the use of a sentinel organism and several markers for early warning of pollution measured in different tissues, may prove useful for monitoring the health of the environment, animals and humans from a one health perspective.