Data presented here were collected between April 2017 to December 2018 within the BEFmate project (Biodiversity - Ecosystem Functioning across marine and terrestrial ecosystems, https://uol.de/icbm/verbundprojekte/abgeschlossene-projekte/befmate/ ) of the Universities of Oldenburg and Göttingen and the Nationalpark Niedersächsisches Wattenmeer. Experimental islands and salt marsh enclosed plots were created in the back barrier tidal flat and in the salt marsh zone of the island of Spiekeroog.Temperature in the sediment surface layer (in approximately 0.05m depth) was measured with DEFI-T miniature temperature recorders (JFE Advantech Co., Ltd., Tokyo; DEFI-T). The manufacturer pre-calibrated temperature recorders and were installed on the experimental islands and in salt-marsh enclosed plots at different elevation levels. Recorded data were internally logged until the readout with the DEFI Series software (V1.02). The position was derived from a portable DGPS-system. Date and Time is given in UTC.Data handling was performed according to Zielinski et al. (2018): Post-processing of collected data was done using MATLAB (R2018a). Quality control was performed by (a) erasing data covering maintenance activities, (b) removing outliers, defined as data exhibiting changes of more than two standard deviations within one time step, and (c) visually checks.