ABSTRACT The biology and ecology of Darina solenoides, an abundant bivalve of sandy sediments along Patagonian coasts, is poorly known. Here, we investigated the population dynamics and secondary production of this species in Río Gallegos Estuary (Southern Patagonia, Argentina, 51°35’S, 69°01’W). Sampling was conducted monthly, from April 2014 to June 2015, by collecting 10 samples from the intertidal fringe using a core of 10 cm inner diameter. The sediment was mainly composed of fine and very fine (77.5%) sand; total organic matter content was 1.8%. The average population density was 779.4 ± 56.4 ind m-2 the population was composed of four modal groups. The settlement of a new cohort occurred in April-May each year. The von Bertalanffy growth function was L∞ = 49.4 mm; K = 0.5; the calculated lifespan was 4.2 years. Population somatic production was 80.6 g dry mass m-2 yr−1 and the production-to-biomass (P/B) ratio was 0.96. The observed high production supports the hypothesis that D. solenoides is an important resource for many marine species.