ABSTRACT: A long-term analysis of the structure of a bivalve population consisting of the wedge clam Donax hanleyanus is described for an exposed temperate sandy beach of Uruguay. The potential effects of human harvesting on the sympatric bivalveMesodesma mactroides (yellow clam) and of salinity were analyzed through time and space (longshore variation). Inter- and intra-annual fluctuations of the different population components (recruits, juveniles and adults) were detected. D.hanleyanus showed uneven periods of abundance, with the occurrence of peaks of different magnitude that appeared related to fluctuations in the fishing effort targeting on the yellow clam. D. hanleyanus showed a marked longshore variability inpopulation structure and abundance along the 22 km of sandy beach sampled. Spatial variations in salinity and also in the amount of fishing effort exerted on M. mactroides seem to be key factors in explaining this variation. This study suggeststhat further research on sandy beach populations should include human activities as important factors affecting long-term trends.