Applicability of ecological evaluation tools in estuarine ecosystems: the case of the lower Mondego estuary (Portugal)

In accordance with the Water Framework Directive guidelines (WFD, 2000, European Communities Official Journal L327 2000/60/EC), classification schemes and ecological evaluation tools (based on benthic invertebrate fauna data sets from 1990 to 2002) were applied in the lower Mondego estuary. Two distinct scenarios could be tested due to the implementation of mitigation practices in 1999, following a long eutrophication process, which started by the early 1980s. Some discrepancies in the results were found by the application of the different indices. The AMBI index (accounting for taxonomic composition) and the ABC method (accounting for abundance and biomass k-dominance patterns) classifications often disagreed with those based on species diversity (Margalef and Shannon-Wiener). The ambiguous results made the classification a complex task to achieve, contrary to the Directive’s objective of maintaining it simple and clear. Our results suggest the necessity of adjusting some of the indices and their ranges to estuarine characteristics, namely to account the typical dominance and abundance of some particular species. These aspects are not taken into consideration by some of the indices proposed, which are more adapted to typical marine conditions. Based on our results, these widely applied indices might still improve their efficiency in estuarine systems allowing their use in the resembling types already established within the new Directive agenda.