This dataset contains individual-level measurements of the blue mussel Mytilus edulis collected during a controlled mesocosm experiment at Sylt, Germany. Data were collected over a three-month period from 2 April 2022 to 27 June 2022. The experiment comprised twelve mesocosms, with four maintained at ambient temperature, four maintained at +1.5°C above ambient, and four at +3 °C above ambient. Observations include shell length, shell-length growth rates, and multiple biomass fractions, including total wet weight, wet tissue mass weight, shell-free dry weight, and ash-free dry weight, from which weight-based growth rates were calculated. All measurements were obtained using standard, traceable laboratory and field instruments. The dataset documents individual-level growth responses of M. edulis under controlled warming conditions and provides a reproducible resource for studies on physiological responses of coastal bivalves to temperature changes.