LAUSR

The effect on diatom frustule morphology of long-term cultivation at mono-spectral light (six wavelengths combined with two light intensities) was investigated. The results showed that the size of Coscinodiscus granii frustules and the foramen size increased after 10-month cultivation for all light treatments, compared to results after short-term cultivation. The main difference between the light intensities was in the foramen density and similar to the short-term treatment, the lowest density was found at high-intensity red light. Thus, the mean foramen density and foramen diameter at red light 300 μmol photons m−2 s−1 and white light 100 μmol photons m−2 s−1 were statistically similar for short- and long-term tests. The foramen density was significantly reduced at all colored wavelengths at 100 μmol photons m−2 s−1, and blue and white light at 300 μmol photons m−2 s−1 after long-term compared to short-term cultivation. After both short- and long-term experiments, the foramen diameter showed a general trend of higher light intensity resulting in smaller foramen diameter, except for Y light. This study shows that C. granii can be maintained at mono-spectral light over long time periods and indicates that the most important morphological differences are maintained with the range of variability in some of these parameters being more constrained compared to short-term cultivation. This has important implications for mass cultivation of diatoms at different light conditions for applied purposes.