Total wet mass (WM), dry mass (DM) and ash free dry mass (AFDM) were determined for specimens from Station 1 (X-Huinay) covering the entire size range of Aulacomya atra and Mytilus chilensis. For this investigation mussels were sampled in the intertidal zone (M. chilensis) and the shallow subtidal zone (A. atra). The sampling depth ranged from 0 to 20 m below Mean Sea Level (MSL). Mussels were boiled in sea water and immediately removed from it, when shells opened. WM was measured after complete drainage of the water contained in the mantle cavity. The soft tissue was extracted from the shell and DM was established after drying to constant mass at 60 °C for 24 h. AFDM was obtained by subtracting the ash mass, measured after ignition of the soft tissue at 500 °C for 7 h, from the DM.This dataset was generated in the frame of the co-operation between the Huinay Scientific Field Station (http://www.huinay.cl) and the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (http://www.awi.de).