Munida subrugosa is the most abundant benthic species in the Beagle Channel (55°S, 68°W), Tierra del Fuego. Moreover, this species has two simultaneous but different feeding habits: predator and deposit feeder. Because of its high abundance (100 ind·100 m−2) and trophic position, this species plays a key role in the subantarctic benthic ecosystems. However, little is known about its energetic content and changes in dry mass during its reproductive cycle. Samples of M. subrugosa were obtained in 2000 to 2001 by means of an epibenthic trawl. The relative water content (WC) and the energetic content (EC) (kJ·g−1 ash free dry mass [AFDM]) of whole adult animals, and the relative dry mass (RDM) and EC of tissues and organs of females were measured throughout one year. The EC investment of adults at the time of maximum gonadal development was evaluated. The EC was measured using a bomb calorimeter. The mean WC and EC for M. subrugosa was 59% ± 7% and 19 ± 2 kJ·g−1 AFDM, respectively. WC and EC for whole adult animals varied significantly throughout the year, attaining maximum values in autumn or summer respectively, after the pattern of seasonal reproduction and feeding. Moreover, the EC of M. subrugosa varied by 30% annually. The RDM and EC investment in gonadal development was significant higher in females. The hepatopancreas in M. subrugosa is used as an energetic storage organ, because RDM and EC increased before vitellogenesis and moulting.