Intertidal biogenic reefs built by the polychaete Boccardia proboscidea in sewage-impacted areas of Argentina, SW Atlantic

Abstract

The rocky intertidal zone around Mar del Plata city (SW Atlantic, 38º S - 57º W) is characterized by dense mussel beds of Brachidontes rodriguezii. This intertidal community develops on natural and artificial hard substrates, including abrasion platforms in sewage-impacted areas. A monitoring program designed to assess the effect of sewage discharge on intertidal macrobenthic communities has been conducted since 1997. During spring 2008 a new spionid (Boccardia proboscidea) was found in areas near the sewage outfall forming large biogenic reefs. This is the first report of biogenic reefs built by a non reef-forming spionid in areas organically impacted by sewage discharges. The aim of this work was evaluate the spatial-temporal dynamic (% of cover and density of B. proboscidea) of these reefs. Those biogenic reefs covered almost the entire impacted site reaching a density of 650,000 ind.m-2. This phenomenon is worldwide unique and there is no record of other biogenic polychaetes reefs that could be sewage-induced. The presence and stability of these reefs is discussed in relation to the increase of organic contamination as structuring factor of these structures.