Assessing the ecological status of the North-western Adriatic Sea within the European Water Framework Directive: a comparison of Bentix, AMBI and M-AMBI methods

In this paper we looked for the most suitable method for benthic ecological quality status (EcoQS) assessment of the North-western Adriatic Sea. Taking into account the historical and present information, we inter-compared our expectations in terms of EcoQS, with the Bentix, AMBI and M-AMBI classificationmetrics results, and investigated the sensitivity of these indices to the spatial, seasonal and inter-annual variability of benthic communities. The sampling sites were located at increasing distances with respect to the Po Rivermouth, along an (inverse) gradient of eutrophication. Moreover, a 2-year monthly monitoring plan (October 2004–September 2006) was carried out at the CEBEB site, located in a central position with respect to the investigated area. The results highlighted that the three indices differed in the sensitivity to spatial and temporal variability of the benthic communities. The strong seasonaland inter-annual changes in the benthic communities had a significant effect on the Bentix, whereas no relevant modifications were observed on the EcoQS assignation obtained using the M-AMBI and AMBI methods. The environmentalquality ratios (EQR) values and EcoQS classification obtained by the Bentix and AMBI did not match expectations, as they were not inversely correlated with the site distances with respect to the Po mouth, whereas the M-AMBI clearly discriminated the most and the least eutrophicated sites. It thus appears that the M-AMBI could be considered to be the most valuable method for the ecological-status assessment of the North-western Adriatic Seabenthic ecosystem.