Daily striae on the shell of the scallop, Argopecten purpuratus, were used to investigate its growth in a protected population within La Rinconada Bay, near Antofagasta (2^nd Region, Northern Chile), and to determine how environmental forcings control shell growth. This sclerochronological approach was useful to describe daily shell growth a posteriori. Mean shell growth rates were calculated daily between February and October 1999 from shells of six specimens harvested on 15 October 1999. A multiple regression analysis performed on shell growth and environmental data shows that a temperature increase stimulates shell growth whereas particulate organic carbon concentration might be stressful above 2.5 mg L^-1. The lunar cycle might also have an effect on growth, most potent around New Moons, by synchronizing an endogenous oscillator. The age at commercial size (90 mm) was only 10–11 months in La Rinconada Marine Reserve and the von Bertalanffy growth parameters were K = 2.24 y^-1 and H_oo = 117 mm. Differences in shell growth performances between this study and previous ones dealing with A. purpuratus growth may be explained by the different methods used for shell growth modelling, higher growth rate on the seabed compared to suspended cultures, and particular environmental forcings (e.g. El Niño Southern Oscillation-ENSO events). Growth performance seems better during La Niña than during El Niño events, probably because of the large temperature increase (above the highest temperatures recorded in “normal” conditions) and the decline in coastal upwelling (which affects food availability) during El Niño. La Rinconada Marine Reserve appears as a very favourable site for A. purpuratus growth, probably because of the active upwelling zone off Antofagasta. These new insights on A. purpuratus shell growth confirm the importance of La Rinconada Marine Reserve as an area supporting repopulation of endangered wild stocks and scallop aquaculture in Chile.