Lugworms Arenicola marina were collected from Arcachon Bay in two summers and winters of consecutive years. The worms were acclimated to different temperatures (5 and 10 °C for winter animals and 15 °C for summer animals). Each group was investigated over an experimental temperature range concerning its optimum in exercise performance, acute growth rate as well as respiration and ventilation activities to reveal seasonal acclimatisation effects, potential inter-annual differences and the influence of laboratory acclimation temperatures on the parameters of interest. The groups investigated at the two consecutive summers yielded nearly identical results for ventilation and respiration activities. A clear seasonal difference developed in exercise performance, with an optimum at lower temperatures in winter than in summer, irrespective of acclimation temperature. Respiration and ventilation activities showed no significant differences between winter specimens acclimated to 10 °C and summer specimens acclimated to 15 °C. However, an acclimation temperature of 5 °C for winter animals caused noticeable differences to those acclimated at 10 °C. Acute growth rates differed seasonally as well as between acclimation temperatures with the highest rates found around 10 °C in summer and around 15 °C in winter. The lowest rates were recorded in winter worms acclimated to 5 °C. These acute patterns may reflect high thermal limits in warm acclimated winter worms and temperature dependent shifts in energy demand in summer animals.