Suitability of benthic macrophyte indices (EEI, E-MaQI and BENTHOS) for detecting anthropogenic pressures in a Mediterranean coastal lagoon (Mar Menor, Spain)

Different approaches based on macrophytes have been proposed in recent years to implement the European Water Framework Directive. However, their application to transitional environments presents difficulties as a consequence of the natural gradients of environmental conditions in these ecosystems. Three of the most widely used methodological approaches, the EEI, E-MaQI and BENTHOS index were applied under different stress conditions in order to evaluate their suitability for detecting anthropogenic pressures in coastal lagoons. For this purpose, 12 representative sampling stations were selected, including sites that suffer the greatest pressures in the Mar Menor (agricultural and urban wastes that reach the lagoon through the principal watercourses, and pleasure harbours) as well as sites considered to be in good ecological condition. Species respond not only to eutrophication and nutrient concentration gradients, but also to natural environmental stress and confinement. The assessment of stations according to substrate type differed between EEI and E-MaQI, the correlation between the scores assigned by each index being very low. Moreover, the explanatory variables selected by the regression models (GLM) show that the tested indices mainly respond to natural environmental stress and, only after excluding these variables from the analyses, did the relationship of the indices with eutrophic parameters, such as chlorophyll a or ammonium concentration, become evident.