Ability of benthic indicators to assess ecological quality in estuaries following management

Robust approaches to evaluate ecological quality in aquatic ecosystems become demanding concomitantly with the degradation resulting from increasing human-induced pressures. Aiming at a successful management, numerous evaluation tools are currently available and have been widely used for quality status assessment in estuaries mainly through the analysis of macrobenthic communities. The Mondego estuary (Portugal) has been under severe environmental pressure since the early 1990s due to different anthropogenic stresses. To improve the ecological condition and mainly to ameliorate the risk of eutrophication symptoms in an estuarine section (south arm), in 2006, the upstream connection between the north and south estuarine arms was re-established. Data on subtidal macrobenthic communities and environmental variables over a 5-year interval, covering the pre-management (from 2004 to 2006) and post-management (2007 and 2008) periods were used to assess restoration effectiveness. Firstly, temporal differences in the structure and composition of the macrobenthic assemblages between periods were assessed. Secondly, the relative performance of different ecological indicators (Shannon–Wiener, Margalef, Pielou, Simpson, AMBI, taxonomic diversity measures and Eco-exergy based indicators) to capture potential ecological changes between periods was analyzed. Lastly, indicators’ performance was compared with the information given by the analysis of macrofauna composition and structure to distinguish their usefulness for addressing specific management objectives. post-management, water quality did not reflect considerable changes while macrobenthic assemblages responded to restoration variably along the estuarine gradient. Overall, ecological indicators effectively detected the prevailing ecological conditions and behaved consistently with the subtidal community ecological context. Most indicators were able to capture temporal changes in macrobenthic assemblages structure and performed differently for the distinct estuarine zones assessed, not always indicating a quality improvement. Further monitoring and assessment on subtidal macrobenthic communities’ structure and functioning is needed to understand better the restoration effects. Recognize the success of such actions in aquatic systems is crucial for their adequate management.