The effects of some environmental variables on the morphology of Nitzschia frustulum (Bacillariophyta), in relation its use as a bioindicator

Nitzschia frustulum (Kutzing) Grunow is a widely distributed diatom taxon and very common in different types of habitats. It presents a wide range of variation in length, width and shape. The morphological variation of N. frustulum was studied in a culture experiment using specimens isolated from a Mediterranean salt marsh, where environmental conditions fluctuate over a wide range. The effect of three environmental variables on valve morphology was tested in a factorial design: salinity (0.5, 7.0, 17.5parts per thousand); N : P ratio (6.5:1, 16:1, 32:1) and water movement (movement/no movement). Salinity is the main factor affecting length, width and fibula density, but changes in N : P ratio and water movement also affect fibula density and width, respectively. Stria density is the most stable character studied. Short and wide valves were observed in all salinity treatments. The results corroborate the conspecifity of N. frustulum and N. inconspicua, formerly considered characteristic of N. inconspicua, a species limited to freshwater.