Comparing structural and functional approaches to distinguish benthic communities from eutrophic and non-eutrophic estuaries

The performance of three approaches for macrobenthic classification in distinguishing communities subjected to different environmental conditions was compared: i) the traditional species-based approach; ii) a tolerance-based approach according to ecological groups of the AMBI index; and iii) a character-based approach using biological traits. We used a hierarchical sampling design including three progressively smaller spatial scales, considering that the environmental degradation influence benthic communities at the larger spatial scale. Despite small-scale spatial variations, all approaches performed similarly, distinguishing eutrophic from non-eutrophic benthic communities as they varied significantly at the larger scale, corresponding to the scale at which human induced changes act. Our results suggest that all three methodological approaches could be used as operational criteria to assess estuarine environmental quality, and despite more meaningful, there is still a degree of subjectivity in functional approaches, associated to the lack of more detailed information on macrofaunal life-cycles and levels of tolerance to disturbance.