ECOLOGY AND MORPHOLOGICAL VARIABILITY OF AULACOSEIRA-GRANULATA (BACILLARIOPHYCEAE) IN SPANISH RESERVOIRS

The ecology of Aulacoseira (formerly Melosira) granulata and its diffe rent forms in similar to 30 reservoirs scattered throughout Spain has been analysed. Nutrient concentration explained a significant proporti on of the variation in cell characteristics. In general, there is a te ndency to find large cells with less densely areolated valves in nutri ent-rich waters. Ecological differences between the type and its varie ty angustissima mainly concern calcium concentrations. Aulacoseira gra nulata showed a unimodal response to the concentration of calcium, and preferred lower concentrations of calcium than the variety angustissi ma. The ecological differences between the alpha and gamma forms (stat uses) of A.granulata were also the object of our investigation. The ga mma status occurred in all the reservoirs studied in summer, but in on ly 3 of 28 reservoirs studies in the overturn period. Light and turbul ence explained the ecological differences observed between the two for ms. The gamma status showed a certain preference for less turbulent wa ters compared with the alpha status, which is a more cosmopolitan form in its requirements.