Assessing the ecological status within European transitional waters (northeast Atlantic) intercalibrating different benthic indices

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The Water Framework Directive (WFD) has developed several methods to assess the benthic status of European marine waters. WFD implementation requires the intercalibration of such methods, in order to ensure that the status classification is consistent and comparable across countries and water body types. A working group of nine countries (Portugal, Spain, France, Belgium, the Netherlands, Germany, Sweden, Ireland, and the UK) has been established to intercalibrate methods in transitional (estuaries) waters, within the Northeast Atlantic ecoregion. The following steps for intercalibration were agreed upon by this group: (i) to establish common water body types across Europe, based on salinity, tidal range, mixing conditions, intertidal area, and estuary size (six common types were identified); (ii) to compile a common dataset (9337 samples collated, from 59 estuaries and 8 countries, covering 5 out of the 6 types, and most of the ecotopes); (iii) to harmonize the taxonomy of the dataset (using ERMS, WoRMS and Fauna Europaea); (iv) to collate human pressures from each estuary; (v) to set reference conditions for each type; (vi) to calculate ecological quality ratios for each of the 10 methods proposed for intercalibration (BAT, M-AMBI, BOPA, BO2A, QSB, MISS, BEQI, AETV, BQI, IQI); (vii) to interpret the response of these methods to different anthropogenic pressures; (viii) to determine boundaries for each of the five quality classes (from bad to high status), using the 10 methods; and (ix) final agreement in the assessment and intercalibration. This contribution presents the steps already taken and the way forward in this intercalibration exercise.