Mediterranean lagoon ecosystems are particularly sensitive to Climate Change (CC) events that include rapid reductions in salinity (e.g., flash flood) and increase of seawater temperature represent major stressors for bivalve populations. Continuous monitoring of behavioral responses can provide a sensitive indicator of physiological stress. This study used Hall sensor valvometry to investigate the valve-gaping behavior of the clam Ruditapes decussatus exposed to two environmental stresses, the first simulating a drastic reduction of salinity (35, 20, 10 and 5 PSU) and the second an anomalous increase of temperature (22, 24, 26, 28 and 30 °C). The entire experimental setup was housed in independent aquaria units called Technological Aquarium Racks system (TARs) to minimize external disturbances to valve opening behavior, allowing for the independent manipulation of multiple environmental stressors under controlled laboratory conditions. Four behavioral descriptors were calculated from normalized valve-opening data: Average Valve Opening (AVO), Proportion of High Opening (PHO), Probability of Near Closure (PNC) and Number of Closure Events (NCE). Behavioral responses were analysed using linear mixed-effects models and beta-binomial generalized linear mixed models. Progressive salinity reductions decreased AVO and PHO while increasing PNC and NCE, indicating suppression of filtration activity and activation of defensive valve-closing responses. A marked threshold was identified between 20 and 10 PSU below which valve activity rapidly declined. At 5 PSU salinity the PHO disappeared completely, suggesting an almost complete interruption of filtration. Rapid behavioral responses to osmotic stress were observed with no significant effect of exposure time.

Increasing temperature led to an increase of AVO and PHO between 26 and 30 °C whereas NCE progressively decreased, indicating longer and more stable valve opening periods. Temperature × time interactions demonstrated that behavioral responses progressively changed throughout exposure, whereas PNC remained unaffected, indicating that the tested temperatures did not trigger defensive valve closure.

These findings demonstrate that Hall sensor valvometry provides a sensitive, high-resolution approach for detecting early behavioral responses of R. decussatus to climate-related environmental stressors, supporting its application for ecological monitoring and aquaculture management in Mediterranean coastal ecosystems.