Variation of the rocky intertidal community around a sewage discharge in the Peruvian central coast

FIRSTATER F. N.; HIDALGO F. J.; LOMOVASKY B. J.; TARAZONA J.; FLORES G.; IRIBARNE O. O.

Lima

Simposio; Censor Endterm Symposium; 2008

Despite the increasing impacts of the sewage contamination on intertidal shores, the effects of sewage nutrient on the benthic assemblages in upwelling systems remain unclear. Here we describe the spatial variation of the intertidal assemblage at the local scale, related to a point-source disturbance in Ancón Bay (Peru). We also analyze the relative effects of herbivores and nutrients concentrations in the succession of the intertidal rocky shore community. Through measurements of nutrients concentrations and stable isotope analyses we found a significant input of nutrients at the outfall of Ancón Bay, which enhanced macroalgal nitrogen content. However, the localized impact of nutrients was not reflected in algal assemblage, but in the abundance of some invertebrates. During succession, cover of sessile organisms varied both at the temporal and spatial scale. Grazers only affected one macroalga, enhancing its cover. However, differences in patterns could not be attributed to discharge effects. Independently from the outfall distance, the community development seems to be bottom-up controlled in the entire bay, probably because of upwellings that operate at a larger temporal and spatial scale. Although the localized impact of sewage discharge, we suggest that in nutrient-rich systems, environmental factors are more important than anthropogenic-derived nutrient in shaping intertidal community structure.