Blue light regulates the rhythm of diurnal vertical migration in the raphidophyte red-tide alga Chattonella antiqua

Abstract

We examined the effects of photoperiod, wavelength and light fluence rate on diurnal vertical migration (DVM) cycle in a coastal raphidophyte, Chattonella antiqua. We first observed the DVM under different combinations of lightdark (LD) cycles and light spectra. Under continuous white, UV-A or blue light, DVM followed the LD cycle established during the white light pre-conditioning, for one cycle, and then became arrhythmic. Under red light, however, the DVM rhythms under the different LD regimes continued approximately as during pre-conditioning. When C. antiqua cultured under continuous red light was exposed to a 2-h pulse of blue light at the beginning or end of artificial night, the DVM was delayed or advanced, respectively. The fluence rateresponse curve indicates a blue-light threshold of 10(2) mol photons m(2) s(1) for the DVM phase shift. The equal-quantum action spectra for phase shift peaked in the UV-A/blue region (360480 nm), which is the part of the light spectrum most transmitted in its natural habitat. We show that C. antiqua can sense the weak blue component of sunlight throughout its depth range, allowing it to cue its DVM to the daynight cycle regardless of weather and transparency.