Physiological plasticity and life history traits affect Chamelea gallina acclimatory responses during a marine heatwave.

The striped venus clam (Chamelea gallina) is a relevant economic resource in the Adriatic Sea. This study explored the physiological status of C. gallina at four sites selected along a gradient from high to low incidence of recorded historical mortality events and low to high productivity in the Northwestern Adriatic Sea. Investigations were performed during the marine heatwave in 2022 (from July to November). The optimal temperature range for C. gallina was exceeded in July and September, exacerbating stress conditions and a poor nutritional status, particularly at the low productivity sites. Transcriptional profiles assessed in digestive glands showed that clams from the low productivity sites up-regulated transcripts related to feeding/digestive functions as a possible compensatory mechanism to withstand adverse environmental conditions. Clams from the high productivity sites, that in a previous study showed enrichment of health-promoting microbiome components, displayed a healthier metabolic makeup (IDH up-regulation) and induction of protective antioxidant and immune responses. These features are hallmarks of putative enhanced resilience of the species towards environmental stress. Despite the well-known high sensitivity of C. gallina to environmental variations and its narrow window of acclimatory potential, results highlight that local conditions may influence physiological plasticity of this clam species and shape either positively or negatively its response capabilities to environmental changes. The identification of health-promoting endogenous mechanisms both from the animal (this study) and from its associated microbiome may provide the foundation for developing novel tools and strategies to improve clam health and production in low productivity areas or under adverse environmental conditions.