PHYSIOLOGICAL ENERGETICS OF CONCHOLEPAS-C ONCHOLEPAS (BRUGUIERE, 1789) (GASTROPODA, MURICIDAE) IN YALDAD BAY, SOUTH OF CHILE

The main physiological processes representing the energy gain (ingesti on and absorption) and the energy lost (oxygen uptake, excretion and m ucus production) were quantified seasonally in five size classes of th e gastropod Concholepas concholepas (Bruguiere, 1789) fed with an ''ad libitum'' diet of the mussel Mytilus chilensis. Ingestion rate was hig hly dependent of body size, with higher values during spring and summe r, suggesting a relationship with the reproductive condition of Concho lepas concholepas and also with the increasing temperature. Absorption efficiency was independent of body size, showing the higher values du ring autumn and winter, when C. concholepas showed the lower ingestion rates. Ammonia excretion showed a significant correlation with body s ize and accounted for a low percentage of the total absorbed energy (2 -7%). The higher values occurred during spring, showing that this phys iological process is not only temperature depending, but other factors such as the reproductive state and the energy storage cycles can play an important role. Oxygen uptake did not show significant differences between day and night, probably due to the ''adlibitum'' diet supplie d to C. concholepas immediatelly before the measurements, which could reduce the high foraging activity described for this species in the da rk. Oxygen uptake was higher in spring in the larger individuals, sugg esting that the seasonal fluctuations of this physiological process is more dependant on the reproductive condition of C. concholepas than o n water temperature. Mucus production was mainly related with the acti vity of locomotion of C. concholepas. The energy lost in mucus represe nted a significant percentage of the total absorbed energy, being conv enient to include this measurement in the physiological studies on gas tropods. The scope for growth and net growth efficiency were higher du ring summer and spring, decreasing in winter to show negative values d uring autumn, This seasonal pattern was mainly caused by the amount of energy gained (ingestion, absorption) and secondly by energy expendit ure in respiration. It is possible to conclude that C. concholepas is able to present positive energy balances during large part of the year when fed ''adlibitum'' on the bivalve Mytilus chilensis. The estimate d scope for growth under laboratory conditions is in agreement with th e seasonal growth pattern observed on natural populations of C. concho lepas of south of Chile.