Benthic prey quantity and quality in the main mudflat feeding areas of the Tagus Estuary: Implications for bird and fish populations

Abstract

Estuaries are among the most productive environments in the coastal zone that may act as sink of pollutants. In this study we evaluated how levels of heavy metal contamination can be reflected in the macroinvertebrate communities of six Tagus Estuary mudflats, inferring their consequences to upper trophic levels. We used Shannon-Wiener’s diversity, Pielou’s evenness and Simpson’s dominance indices, and macroinvertebrate densities to characterize benthic communities at the sites that presented different metal contamination loads. Those stations with high levels of contamination presented a lower diversity but also the highest prey density. This study indicated that unhealthy areas can still perform their ecosystem function with costs that remain to be evaluated. The biodiversity can be impoverished compared with other less contaminated sites, but with regard to their utilization as feeding areas by birds and fishes this is not a limiting factor. For this particular function of the mudflats, prey availability is the main characteristic determining the choice of one particular site as a bird and fish feeding area that may not be affected by heavy metal contamination.