Multi-metric index based on the seagrass Zostera noltii (ZoNI) for ecological quality assessment of coastal and estuarine systems in SW Iberian Peninsula

► The ZoNI index was developed for ecological assessment of waters from SW Iberian Peninsula. ► Environmental and seagrass variables were analyzed using principal component analysis. ► Seagrass metrics and environmental variables were significantly correlated. ► The ZoNi index is valid to classify coastal waters according to their ecological status.