The ecology and taxonomy of estuarine benthic diatoms and their use as bioindicators in a highly stratified estuary (Ebro Estuary, NE lberian Peninsula)a multidisciplinary approach = L’ecologia i la taxonomia de les diatomees bentòniques estuarianes i el seu ús com a bioindicadors en un estuari altament estratificat (l’estuari de l’Ebre, NE Península Ibèrica): un estudi multidisciplinari.

Résumé

The general aim of the thesis was to improve knowledge of the ecology and taxonomy of estuarine benthic diatoms in a highly stratified Mediterranean estuary, in order to evaluate their potential use as bioindicators of this ecosystem. To achieve that, diatom community composition was described and the factors affecting its composition and distribution were elucidated. Once the main anthropogenic pressures in the Ebro Estuary had been established, the response of diatoms to these pressures was tested through: i) the evaluation of existing diatom indices, and ii) the identification of groups of species indicative of potentially altered environmental conditions. Field studies were supported with experimental studies to test the response of species to the main environmental gradient in the Ebro Estuary (i.e. salinity). Several taxonomical aspects of estuarine diatoms were studied in detail to aid in the understanding and interpretation of ecological results. First of all, the morphological variability and ecophysiological response of selected species to salinity was documented. The morphology of the valves of several small and morphologically similar diatom species from the genus Nitzschia (one of the most abundant in the Ebro Estuary) was compared and studied in detail. Finally, the thesis focused on a species complex, i.e. Nitzschia inconspicua, to analyse the morphological, genetic, reproductive and ecophysiological variability of a taxonomically difficult but ecologically important species of both freshwater and transitional waters.