Impact of sewage pollution on the structure and functioning of a rocky shore benthic community

Abstract

The secondary production of rocky shore macroinvertebrate assemblages impacted through sewage discharge was assessed, taking into account the trends of production among dominant species and feeding guilds. The present study was conducted on the Peniche peninsula (central-western Portuguese coast, temperate region), in three areas: one area near a sewage discharge and two undisturbed reference areas. Within each area, three intertidal zones were monitored ‐ littoral fringe, eulittoral and sublittoral fringe ‐ by taking seasonal samples during one year. The empirical model of Cusson and Bourget (2005) was used to evaluate secondary production. In the littoral fringe, no differences in the production values were found between impacted and reference areas. In the eulittoral, sewage discharge seemed to affect the natural competition between patellidae and barnacles by favouring suspension feeders (barnacles), presumably due to higher food resources near the sewage. In the sublittoral fringe, near the sewage discharge, an increase in the production values of tolerant species was observed to the detriment of the sensitive species, with higher production levels in the reference areas. Overall, secondary production was higher in the communities near the sewage affected areas, but this increase was mostly due to the production of tolerant species. The present study showed that the incorporation of secondary production in the biological assessment provided further insight into the health of the ecosystem, thus being an important tool for understanding differences in the functioning of the ecosystem.