Robustness of the Estuarine Fish Assessment Index (EFAI) regarding water body definition criteria

According to the Water Framework Directive (WFD) transitional waters should be differentiated according to type and, in some cases, divided into different water bodies. This raises a dilemma in trying to define parts of a continuum. In the sequence of WFD several indices have been proposed including the Estuarine Fish Assessment Index, which can be applied taking an estuary as a whole (EFAI – without water bodies division) or divided in water bodies (EFAIWB). The purpose of this work is to analyze the robustness of the Estuarine Fish Assessment Index, based on three different ways of dividing Portuguese estuaries into water bodies according to different criteria (criterion 1 – distance to the estuary mouth, criterion 2 – salinity and criterion 3 – morphology, salinity and human dimension as pressure and state). In this study we evaluated at which degree these three criteria could influence the ecological quality ratio (EQR) results, when the index was applied to water body level (EFAIWB). Also, for each estuary, the EQRWB results for each criterion of EFAIWB were combined and weighted according to the water bodies areas (EFAI overall weighted – EFAIOW). Finally, it was compared if the results obtained for each criterion with the EFAIOW were similar to the results of the index application taking the estuary as a whole (EFAI – without water bodies division). No significant differences were found in both cases, which indicated that this index is a robust method regarding the division of the estuaries in different water bodies, which is an important element of a fish-based multimetric tool for assessing estuarine ecological quality. However, in some cases, different ecological quality statuses were achieved when applying the EFAIOW or the EFAI. This work addressed several aspects regarding the possible division of water bodies at the WFD context.