In coastal productive environments, such as upwelling systems, sewage effluents might represent an important input of nutrients affecting intertidal community development and structure. Using descriptive and experimental approaches, the community spatial variation and early succession in relation to a point-source effluent discharge in a rocky intertidal of an upwelling affected area (Ancón Bay, Peru) was analysed. The relative contribution of herbivory to the observed patterns was also analysed. Dissolved nutrient concentrations, macroalgal isotopic signatures and N content revealed a significant input of nutrients at the outfall, although this contribution was not reflected in the algal assemblage, but in higher abundances of mytilids, ophiuroids and limpets. Cover of most sessile organisms (biofilm, Ulva spp., mytilids and barnacles) varied among sites throughout early succession, and grazers only enhanced the cover of the red algae Gelidium spp. Differences in succession patterns could not be attributed to discharge effects. The results of this study suggest that the community development is bottom-up controlled in the entire bay, which is likely to be due to the upwelling that operates at larger temporal and spatial scales. If so, nutrient input derived from coastal upwelling may sometimes overwhelm the role of anthropogenic nutrient loadings in shaping intertidal communities.
Method for monitoring intertidal communities in a steep rocky shore: a combination of digital image technology and field operational strategy