## 1 Introduction  
Global climate change is one of the main challenges the world faces, seriously affecting coastal ecosystems. In particular, the increasing occurrence and intensity of extreme climatic events (e.g., floods, droughts and heat waves) often lead to abrupt changes in temperature, salinity and hydrodynamic conditions [1]. This results in impacts on organisms (e.g., physiological processes, behaviour, and mortality), leading to changes in population abundance, community structure and ecosystem functioning [2]. Since this trend is expected to continue, further impacts on aquatic ecosystems are predictable [3, 4]. As such, understanding how biological communities respond to these scenarios is essential for coastal ecosystem management. Bivalves are key species of estuarine and coastal macrofaunal communities, since they usually are: (i) long-lived and large-sized species dominating the assemblage biomass [5]; (ii) highly abundant and productive [6]; (iii) economically valuable as a food resource, being frequently harvested and produced in aquaculture [7, 8, 9]. Moreover, they perform essential ecological functions in the ecosystem, as they influence the benthic-pelagic interface through sediment reworking, resuspension and filtration activities, promoting nutrient regeneration and contributing to water column purification [9, 10, 11]. As such, they play a key role in the ecosystem food web [12]. The cockle _Cerasstoderma edule_ ([PERSON], 1758) is a common species along the NE Atlantic Ocean and through the Baltic, Mediterranean and Black seas-Latitude: 70\({}^{\circ}\) N to 16\({}^{\circ}\) N [7, 13, 14]. It usually inhabits intertidal and subtidal muddy/sand or sand banks on semi-sheltered coastal and estuarine systems [7; 14; 15], preferentially on higher salinity areas located downstream [7; 16; 17]. _C. edule_ is a suspension feeder that burrows just below the sediment surface and filters water above the sediment/water interface [14; 18; 19]. It feeds on phytoplankton, zooplankton, suspended organic matter and microhydrobethos [18; 20; 21; 22; 23] and is usually preyed on by crustaceans, fishes, and wading birds, being a link between primary producers and consumers [19]. Additionally, it is extensively harvested and produced in aquaculture for human consumption throughout its range [7; 24; 25; 26] having a large economic interest [9; 25; 26]. _C. edule_ is usually subjected to great physiological stress related to high gradients and variability of abiotic factors, typical of transition habitats [27; 28]. Salinity is a key physical factor for estuarine bivalves and determine the limits of their geographic distribution and biological features [16; 29; 30]. As an eurylahine species, _C. edule_ can survive in a wide range of salinities, being commonly found in habitats where salinity changes regularly (e.g., estuaries) with daily tidal cycles and seasonal freshwater inflows driven by precipitation. However, the increasing frequency and intensity of extreme climatic events is additionally demanding for these organisms [30; 31; 32; 33], which must endure augmented osmotic stress [27; 28]. Short-term (tidal) and long-term (rain periods) salinity changes generate an osmotic gradient between the ambient medium and the organisms, often leading to behavioural and physiological responses [34; 35; 36] and ultimately to mortality episodes [8; 19; 37]. In a previous laboratorial experimental study, [PERSON] et al. [16] showed that _C. edule_ is negatively affected by low salinities, being particularly vulnerable to floods. One of the main observations was the absence of burrowing behaviour on salinity treatments <10 [16]. At first, this could be considered as a simple protection strategy: organisms submitted to low salinity close their valves and suspend their activity, shielding themselves from the osmotic stress. However, _C.