Physical effects of an invading reef-building polychaete on an Argentinean estuarine environment

Although the environmental impact of invasive species is variable, ecosystem engineers usually dramatically modify the ecosystem through different mechanisms. Here, we evaluated physical effects generated by Ficopomatus enigmaticus, an exotic and ecosystem engineer reef-building species, in one of the largest coastal lagoon of Argentina. To address this issue we analyzed aerial photographs covering 24 years of invasion and we performed short-term sampling and experiments. Our results show that the density and size of the reefs in the lagoon have increased reaching up to 370 reefs ha(-1) and 7 in in diameter, respectively, in the last 24 years. At a local scale, we found that finest sediments settle on the top and leeward side of the reefs, whereas coarse sediments settle on the windward side. In addition, reefs altered both the bedload sediment transport and the relative water flow around them and these processes were related with both speed and direction of the wind. The results strongly suggest that the overall magnitude of the physical effects generated by this ecosystem engineer is much greater, considering that reefs invaded most of the lagoon. (C) 2003 Elsevier Ltd. All rights reserved.