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Assessment of the ecological status of north-eastern Adriatic coastal waters (Istria, Croatia) using macroalgal assemblages for the European Union Water Framework Directive

Based on the inclusion of macroalgae in the European Union Water Framework Directive as quality elements for the evaluation of the ecological status of coastal waters, the suitability of one (Ecological Evaluation Index, EEI) of several previously proposed evaluation methods in the particular ecological conditions of the northern Adriatic Sea was tested. The EEI was assessed for 10 locations (polluted and putatively pristine) scattered along 60 km of the western Istrian coast. The sampling was performed seasonally at 1 and 3 m depth by destructive (determination of species cover and biomass) and non-destructive (determination of species coverage using digital photography) methods. When assessed at 1m depth the spatial scale weighted EEI for the west Istrian coast was 8.1, corresponding to an ecological status class (ESC) value of high. However, data for 3 m depth gave a spatial EEI of 6.72 which corresponds to an ESC value of good. Regressions of the ratio of ecological state group I (ESG I, i.e. thick leathery, calcareous and crustose species) over total algal abundance with the pollution gradient (obtained using PCA ordination of environmental variables) were significant at 3 m but not at 1 m depth. This was due to high abundance of ESG I macroalgae Corallina elongata and Cystoseira compressa at 1m depth at polluted stations. Similar regressions were obtained using cover, biomass and coverage. It is concluded that the EEI method may be suitable for the classification of coastal waters in the northern Adriatic only in certain cases. A better assessment of ecological status using this method would require more realistic estimations based on the inclusion of data from several sampling depths. As all three abundance measures(cover, biomass, coverage) gave similar results, coverage (using digital photography) is suggested as being a more preferable measure due to rapidity of sampling at several depths and less time-consuming laboratory work.

Water Framework Directive ; ecological evaluation index ; benthic macroalgae ; Istria ; northern Adriatic ; rocky bottom ; Cystoseira ; Corallina

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