Vertical migratory rhythms of benthic diatoms in a tropical intertidal sand flat: influence of irradiance and tides

Vertical migratory behavior of benthic diatoms is one of the adaptive strategies employed for a life in intertidal habitats. Irradiance and tides are considered to be the key factors governing vertical migration. Experiments were carried out to determine the influence of these factors in a tropical intertidal sand flat. Rising to the sediment surface for fulfilment of their light requirements for photosynthesis was the first priority. If not fulfilled during the low-tide exposure, diatoms could withstand the tidal effects and stay up at the surface even during the high-tide coverage. In the laboratory experiments, where the effects of tides were removed, the endogenous clock continued to operate in a similar fashion to that in the field when under 12-h light:12-h dark conditions, whereas continuous darkness induced a tidal rhythm. In continuous light, diatoms preferred to stay up longer than was observed in field. The above-mentioned observations reveal that irradiance has a stronger effect than tides in controlling/regulating microscale migrations in benthic diatoms. In addition, temporal differences in the irradiance and the resulting changes in diatom migration can have implications for littoral primary productivity.