Abstract

Geographical variation in species richness in the genera Audouinella (Rhodophyta), Cystoseira (Phaeophyceae) and Cladophora (Chlorophyta) in the western Mediterranean Sea was analysed by using a hypothetical-deductive procedure. For this purpose, the continental shelves close to ten hydrographical watersheds were used as operational geographic units, and the number of species in each of the three genera, as well as the species of the three genera pooled together, were correlated with several environmental variables. No significant relationship was found between species richness in Audouinella and the environmental variables considered in the study, whereas a U-shaped relationship was found between Cystoseira richness and current flow. For the genus Cladophora, a linear relationship between species richness and current flow was obtained. For the three genera pooled together, a multiple linear model was obtained for species richness as a function of current flow and the distance from the Strait of Gibraltar, following the main current in the Mediterranean Sea.