The larval supply in benthic species is an important component for successful recruitment, and knowledge of its processes helps in understanding population dynamics. The present work describes temporal and spatial variations in larval supply of Mytilus chilensis and Choromytilus chorus in 3 sites on the coast of Seno de Reloncaví, and their relation with environmental variables (temperature, salinity and wind component). The presence of competent larvae of M. chilensis and Ch. chorus presented variations in space and time, explained by the variables year, month and location, and additionally for M. chilensis, the east-west wind component. The magnitude of larvae availability for both species was explained too by the year, month and locality variables, suggesting this variable, effects on a local scale. The greatest abundance of competent larvae, observed on the north-east coast of Seno de Reloncaví, was associated with low salinity and temperature values, suggesting the intrusion of waters from the Reloncaví Estuary. Extensive banks of mytilids have been identified in this zone, which may be acting as a larva source for the Seno de Reloncaví.