Current and future thermal habitat suitability of the European clam Ruditapes decussatus (Linnaeus, 1758) in Mediterranean coastal lagoons

The European clam Ruditapes decussatus contributes to ecosystem functioning and supports fisheries in coastal lagoons across the North-Eastern Atlantic and Mediterranean. Although the ecological consequences of climate-driven warming in lagoon systems are increasingly documented, its implications for the spatial distribution and habitat suitability of benthic species remain poorly understood. To address this gap, we quantified the metabolic response of R. decussatus across a wide range of temperatures (8-38 °C) by measuring respiration rate (RR). RR increased with temperature, from low values at 8 °C (0.07 ± 0.04 mg O2 h−1 g−1 DW) to a maximum around 26 °C (1.55 ± 0.40 mg O2 h−1 g−1 DW), followed by a sharp decline at higher temperatures. Among 24 candidate Thermal Performance Curve (TPC) models, the best-fitting function indicated an optimal temperature of 26.7 °C and a critical thermal maximum of 38.0 °C. TPC-derived parameters were then used to generate seasonal maps of Thermal Habitat Suitability (THS) under reference conditions (2017-2022) and future climate warming scenarios (RCP 4.5 and RCP 8.5 for 2050) across four Mediterranean lagoons. Under reference conditions, THS showed seasonal and spatial variability, with highest suitability during summer and early autumn and lower values in winter. Future projections indicate a seasonal reshaping of habitat suitability, with increased values during winter, spring, and autumn, and a moderate decline during summer (up to 4% under RCP 8.5). Climate warming may therefore reshape the reproduction timing of the species, with implications for population dynamics and ecosystem functioning. Integrating THS into management frameworks may support future aquaculture and conservation planning.