Is the biological classification of benthic diatom communities concordant with ecotypes?

In this study a biological classification based on diatom communities (a posteriori classification) was used to search for the most appropriate a priori classification in reference conditions, on the basis of 31 reference sites encompassing eight watersheds in the NE Iberian Peninsula. We considered three different a priori systems for comparison: (i) a typological classification (ecotypes and subecotypes) based on geomorphology and water flow; (ii) the watershed as a unit, irrespective of its size; and (iii) a classification based on the geographical distance between sites under the assumption that biological characteristics are increasingly similar in geographically closer sites. Classification in ecotypes and subecotypes was the most robust with minor differences between them. The watershed (hydrological units) classification was significant though weaker than the typological classification and there was a larger environmental variation within watersheds than within ecotypes. Finally, results showed that geographically closer sites were not more biologically similar in terms of diatom community composition. We can conclude that the ecotypological environmental-based classifications developed by the local water agency did adequately describe the biological classification based on epilithic diatoms.