Abstract

We experimentally tested three alternative hypotheses to explain the low algal diversity and abundance in an intertidal zone receiving the effluents of the copper mine El Salvador in northern Chile. Our results demonstrated that algae were able to grow at the levels of dissolved copper detected in coastal waters of the area. During the assays, growth and regeneration in several red, green and brown adult algae and juvenile Lessonia nigrescens were normal at copper levels of 150 mu g L-1 or, in some cases, higher. We also found that the coastal sea water mixed with the effluent was not lethal to algae, although in some cases minor effects on growth were detected. These results indicate that today's low algal diversity and abundance can not be explained by the current copper levels in the area nor by the effect of the effluent. Exclusion of grazers, however, resulted in a fast colonization by various algal species. This, together with atypically high grazer density at the areas under the influence of the effluent, strongly suggests that herbivory, a factor not directly related to the mining operation, is likely to be responsible for the low algal diversity and abundance in the studied locality.