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Abstract
The vertical migration behaviour of diatom assemblages as affected by changes of salinity, light intensity and time of day after (re-)mixing has been studied in the laboratory using Low temperature scanning electron microscopy and epifluorescence light microscopy. Further, the response in migratory speed towards changing salinities was investigated.
The migration of diatoms to the sediment surface was partially inhibited by darkness but strongly enhanced by light. Inhibition and enhancement were reversible. Increasing light intensities led to increases in cell numbers on the sediment surface and resulted in variations in species composition migrating to the sediment surface. Diatoms were most responsive to light for upward migration in the morning; remixing or mixing around noon or afternoon resulted in fewer cells migrating to the surface. Maximum upward migratory behaviour was found at 35 ppm salinity. Fewer cells surfaced when the salinity was either lowered or increased. The migratory speed which was approx. 1 μm/s averaged over the entire diatom population remained similar during experiments in which salinity was either lowered to 5 ppm or increased to 60 ppm.
