This dataset includes data from an experimental study on thermal physiology in four carabid beetle species from a freshwater tidal marsh in the Elbe estuary. Individuals of Carabus auratus, C. granulatus, C. nemoralis and Limodromus assimilis were exposed to a series of temperature treatments. Oxygen consumption was measured via optical respirometry (FireSting) to calculate metabolic rate and body-mass loss was measured as proxy for water loss. The dataset contains the processed values used for statistical analysis with associated specimen and experimental metadata.

Abstract Estuarine marshes are characterised by strong thermal and hydrological variability, which influences the physiology and activity of ground-dwelling arthropods. For small ectotherms, such fluctuating conditions can create strong physiological demands, affecting both metabolic reactivity and desiccation risk. Energy expenditure and water loss was measured across four temperature treatments (5, 10, 20 and 25°C) in four abundant carabid beetle species, Carabus auratus, C. granulatus, C. nemoralis and Limodromus assimilis, collected in a freshwater tidal marsh of a large German estuary. By combining both traits, this study compared how species with different habitat requirements and activity patterns respond to the same thermal gradient, and whether occurrence along a hydrological gradient within the marsh is reflected in physiological variation. Energy expenditure was quantified using optical respirometry and water loss was estimated from changes in body mass over three-hour intervals at each temperature. Energy expenditure increased with temperature, but species differed in the intensity of this thermal response. Total water loss varied more among species than among temperatures, with L. assimilis showing consistently higher mass-specific water loss, whereas the three Carabus species showed comparatively low and stable losses. Individual oxygen consumption was a significant positive predictor of water loss. However, most interspecific variation in water loss likely reflected differences in cuticular permeability and habitat-associated behavioural strategies, rather than metabolic rate alone. Taken together, our results highlight pronounced species-specific differences in thermal responses and water-balance strategies within the same marsh community, with implications for how carabid species may respond to future changes in temperature and flooding regime. Simultaneous measurement of gas exchange and water loss is therefore highly effective for linking physiological traits to habitat use across thermal and hydrological gradients.

This project was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), within the Research Training Group 2530: "Biota-mediated effects on Carbon cycling in Estuaries" (Grant/Award Number: 407270017/RTG2530).