Macrobenthic community characterization of an estuary from the Western coast of Portugal (Sado Estuary) prior to dredging operations

Abstract

The present work is part of an environmental assessment undertaken in the Sado estuary (Southern Channel and Mitrena Peninsula), western coast of Portugal, on February 1999 prior to maintenance dredging works. The macrofauna communities in the study area are generally rich and abundant. A single exception was found: a sampling site in the Mitrena area, with extreme impoverishment, probably related to sediment characteristics, i.e., fluid mud, unfavourable to the establishment of individuals. A comparative analysis of these macrofauna results to previous data from 1986 showed that this biological component had suffered no significant changes, especially as far as the most characteristic species. Although the Southern Channel had been dredged in 1995, no clear signs of such operation were apparent in the present survey. The main differences between both periods (1986-1999) was an increase in the abundance and presence of some common species of organic enriched areas, such as Tharyx sp., Corbula gibba, Spiochaetopterus costarum and Ampelisca spp., which might be related to organic enrichment in the Southern Channel. The joint consideration of our results on benthic macrofauna and those regarding sediment contamination and sediment bioassays, performed at the same time by other researchers, does not indicate the necessity of any particular constraints on the dredging operations.