Uncommon species diversity values in epiphytic diatom assemblages of the kelp Eisenia arborea

Macroalgae are an ideal substratum for multiple species of diatoms that are ingested along with their hosts by many species of grazers including abalones (Haliotis spp.). Much of the diet of abalones along the western coast of the Baja California peninsula (Mexico) depends on blades of the kelp Macrocystis pyrifera that is heavily colonized by diatoms. Although the kelp Eisenia arborea (its ecological alternative) is an acceptable food-source for Haliotis spp., the epiphytic diatom flora living on this kelp was hitherto unknown. Thus, the association structure of the epiphytic diatoms growing on blades of E. arborea from the western coast of Baja California Sur (B.C.S.) was determined. We tested the hypothesis that the epiphytic diatom assemblages on blades of E. arborea collected at different dates would show low species diversity and taxa representing distinct stages of succession. We identified 99 diatom taxa that represent the first floristic list of diatoms living on E. arborea. Values of diversity (H´) were lower than usual and, together with an extremely high dominance of Pteroncola inane (a new record for the region), the structure of the diatom assemblage is regarded atypical, similar to those measured for assemblages from extreme environments. However, structure analysis did not permit distinction of succession stages in the epiphytic diatom assemblage