Human exclusion from rocky intertidal of Las Cruces, central Chile: effects on Durvillaea antarctica (Phaeophyta, Durvilleales)

On the exposed rocky shores of central Chile there exists a continuous small-scale harvesting of bull-kelp Durvillaea antarctica, by 'mariscadores' (shellfish and algae gatherers). These harvest both fronds and stipes for human consumption. To assess the effects of human activity on D. antarctica populations, the density, standing crop and size structure of the kelp were compared in nonharvested (fenced) and regularly harvested (unfenced) areas. Both coastal mainland and small islands were included in the fenced and unfenced areas. Unfenced islands were expected to receive less human disturbance than unfenced mainland areas, because the islands were less accessible to harvesters. Populations of kelp underwent great fluctuations in abundance throughout the study period Comparison between harvested and non-harvested areas revealed significant differences in density, biomass and size structure In contrast, no significant differences were found between nearshore islands inside and outside the fenced area. Sources of variation in abundance of populations correspond to recrutment, natural mortality and harvesting, especially in harvested mainland areas. Interaction between tune and extent of exploitation is significant when D antarctica biomass is considered. The existence of protected areas (coastal preserves) and of areas of difficult access to mariscadores (refuges or 'bufferzones') allows the preservation of populations and facilitates re-population of harvested zones.