Are Marine Heatwaves Responsible for Mortalities of Farmed ? A Pathophysiological Analysis of Infected Mussels from Thermaikos Gulf, Greece.

Marine heatwaves (excessive seawater temperature increases) pose high risk to bivalves' health and farming. The seawater temperature increase is responsible for various pathogen population expansions causing intense stress to marine organisms. Since the majority of knowledge so far derives from laboratory experiments, it is crucial to investigate stress responses in field conditions in order to understand the mechanisms leading to bivalves' mortality events after exposure to temperature extremes. Thus, we evaluated the pathophysiological response of the Mediterranean mussel originating from mortality events enhanced by intense heatwaves in Thermaikos Gulf, north Greece, along with infection. Mussels that have been exposed to high environmental stressors such as high temperature were examined for various molecular and biochemical markers, such as , , , and gene expression, as well as the enzymatic activity of the hsp70, hsp90, bax, bcl-2, cleaved caspases, TNFa and ll-6 proteins. Furthermore, histopathology and molecular positivity to sp. were addressed and correlated with the gene expression results. Our findings elucidate the molecular and biochemical pathways leading to mortality in farmed mussels in the context of infection, which according to the results is multiplied by heatwaves causing a significant increase in pathophysiological markers.