STRATEGIES FOR MITIGATING CLIMATE CHANGE AND ANTHROPOGENIC IMPACT IN COMMERCIALLY RELEVANT BIVALVES

The effects of climate change are an undeniable reality that will increasingly lead to severe and negative consequences in the near future. Climate change poses a serious threat to all agricultural production, including the shellfish sector, which is already grappling with rising average temperatures and, more critically, episodes of extreme marine heat waves (MHWs). These events severely impact transitional environments, their resident organisms, and the economic activities that depend on them. Specifically, the production of Manila clams — where Italy, and in particular the Veneto and Emilia Romagna regions, leads Europe — is facing significant economic challenges due to MHWs. Developing effective strategies to mitigate the effects of MHWs is therefore vital to safeguarding the shellfish industry, a key sector for the growth of the blue economy. To this end, understanding both the consequences of MHWs on clams and the adaptive responses they can develop is fundamental. Our results showed that, MHWs reduced clams' energy reserves, activated antioxidant defenses, impaired reproduction, induced dysbiosis in the digestive gland microbiota, and altered animal behavior and filtration rates. Accordingly, we conducted experiments to test two possible innovative approaches to mitigate the effects of climate change on this species: thermal priming and genomic selection. Thermal priming involves exposing animals to sub-lethal heat stress to activate resistance mechanisms, making them less vulnerable to subsequent MHW exposure. We evaluated whether this method could enhance the resilience of Manila clams to MHWs and analyzed its effects, costs, and underlying biological mechanisms in a realistic scenario. Our findings revealed that heat-primed Manila clams exhibited increased tolerance to subsequent lethal heat stress. This was evidenced by higher antioxidant capacity, including enhanced activity of SOD and GPx enzymes in mantle tissue, upregulation of heat shock response genes, activation of lipid and amino acid metabolic pathways in the digestive gland, and a shift in microbial composition favoring beneficial taxa. Notably, we detected evidence of environmental memory lasting up to 38 days after the end of priming, which, to the best of our knowledge, represents the longest recorded environmental memory in mollusks under laboratory conditions. We also investigated whether MHW resistance and the phenotypic plasticity induced by priming were heritable. Although the experimental challenge is complete, we are currently developing a Manila clam SNP array to analyze our samples and quantify the heritability of traits linked to priming-induced phenotypic plasticity and MHW resistance. Identifying major genetic loci associated with constitutive heat resistance and heat-primed responses could not only deepen our understanding of the underlying molecular mechanisms but also pave the way for targeted breeding programs, significantly enhancing the resilience and productivity of farmed clams.