Abstract The effect of small-scale harvesting on populations of Durvillaea antarctica (Chamisso) was studied at four localities in central Chile. Density, standing crop and mean individual size were compared between populations protected from harvesting and those subjected to repeated cropping. Populations on islands, where access by collectors is restricted, were also assessed. Populations of D. antarctica at harvested mainland sites did not differ in abundance (density and standing crop) or mean size. At non-harvested sites standing crops were twice as high as at harvested sites. However, plant density at harvested sites was double that at non-harvested sites. Mean algae size at harvested sites was significantly smaller than at non-harvested sites, because collectors select the largest individuals, usually those with a holdfast diameter of greater than 4 cm. A significant positive correlation was found between wet biomasses present on the islands and those at adjacent harvested and non-harvested mainland sites. Availability of potential space for settlement was also correlated with the density of algae, both on the mainland and on islands. Islands appear to act as seeding grounds or refugial areas, supplying recruits to the adjacent mainland sites. Differences in abundance of D. antarctica between the different localities could therefore be explained by the level of exploitation and by the local geomorphology, particularly the presence or absence of nearshore islands.