Development of a tool for assessing the ecological quality status of intertidal coastal rocky assemblages, within Atlantic Iberian coasts

The aim of this paper is to develop a new methodology for assessing the quality of coastal waters along the Atlantic Iberian coasts, based upon Basque coast rocky intertidal assemblages, compliant with the European Water Framework Directive (WFD, 2000/60/EC). Biological data collected over a 20-year period, during the gradual introduction of a sewerage plan, are compared to several reference stations in order to differentiate various degrees of community alteration. A quality index (RICQI: Rocky Intertidal Community Quality Index) is drawn up, on the basis of: indicator species abundance; morphologically complex algae cover; species richness; and faunal cover (herbivore and suspensivore cover, proportion of fauna with respect to the whole assemblage). An independent dataset collected in Plentzia Bay (Basque coast, N. Spain), before and after the set-up of a wastewater treatment plant, is used in order to validate RICQI. A conceptual model based on our results is proposed, which describes successional stages of assemblages along a gradient of increasing environmental disturbance and associated values of the metrics included in the index. The performance of this new approach is compared with that of the quality of rocky bottoms index, used presently as the official method for assessing the ecological status of rocky assemblages in the Atlantic coastal waters of Spain. Both indices respond to changes in community structure, associated with pollution removal. However, the RICQI index shows a more accurate response, identifying different degrees of disturbance.