Blue light regulates the rhythm of diurnal vertical migration in the raphidophyte red-tide alga Chattonella antiqua
J. Plankton Res. (
Blue light regulates the rhythm of diurnal vertical migration in the raphidophyte red-tide alga Chattonella antiqua
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 light - dark (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 rate - response curve indicates a blue-light threshold of 10 - 2 mmol 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 (360 - 480 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
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sunlight throughout its depth range, allowing it to cue its DVM to the day – night
cycle regardless of weather and transparency.
I N T RO D U C T I O N
Light is a source of both energy and information for
the many biota, especially plants. The spatial, temporal
and spectral variability of light experienced by aquatic
plants represented by phytoplankton differs significantly
from that experienced by terrestrial ones, due to the
selective attenuation of solar irradiance in the aquatic
medium (Ragni and Ribera d’Alcala`, 2004). In the
ocean, the full visible spectrum of white light is found
only at the ocean’s surface, since the sun’s
electromagnetic energy is selectively absorbed and filtered as it
penetrates the upper layers. Infrared and red light is
absorbed and filtered by water itself with green, blue
and blue-green light penetrating the furthest (Jeffrey,
1984). However, in other seas, and especially coastal
waters, blue light fluctuates more than the light of other
wavelengths, and phytoplankton dynamics follow the
attenuation of blue light (Shikata et al., 2009).
Generally speaking, blue light may thus be a stronger
candidate for exploitation as an environmental cue by
marine plankton (Jeffrey 1984; Losi and Ga¨rtner, 2008).
Shikata et al. (Shikata et al., 2009, 2011b) found that
blue light is the most effective for promoting
germination of resting stage cells and growth of vegetative cells
in coastal microalgae such as diatoms. Furthermore,
some blue-light receptors occur in aquatic microalgae
(Iseki et al., 2002; Kasahara et al., 2002; Ishikawa et al.,
2009), although how these work in the actual
environment has not yet been demonstrated.
It has been well known for many years that motility
in flagellate algae is controlled by light. Phototaxis in
microflagellates is a representative example, and blue
light is the most effective out of other components of
visible light for phototaxis in many flagellates (e.g.
Matsunaga et al., 1998; Horiguchi et al., 1999; Iseki et al.,
2002). Furthermore, based on the modeling of spectral
ratios of different light wavelengths together with
measured abundances of major phytoplankton species, it has
also been suggested that spectral ratios of light may act
as complex switches controlling phytoplankton DVM
(Figueroa et al., 1998).
DVM is a biological phenomenon observed in some
flagellate algae including some raphidophytes and
dinoflagellates. They start to swim up to the surface before
dawn and down to deeper layers at dusk (Yamochi and
Abe, 1984; Olsson and Grane´li, 1991; Koizumi et al.,
1996; Park et al., 2001). This DVM enables flagellates to
optimize photosynthesis regardless of the weather and
underwater transparency (Ault, 2000), to acquire
nutrients over a wide depth range (Watanabe et al., 1991)
and to avoid predation by zooplankton which swim to
the surface at night and return to deeper layers in the
daytime (Lampert, 1989). DVM thus aids in
competition with other microalgae such as diatoms, which do
not have this ability (Watanabe et al., 1995; Smayda,
1997; Kamykowski et al., 1998; Salonen and Rosenberg,
2000). Hence DVM is one of the most important
physiological adaptations for survival and growth of
flagellate algae.
It has been suggested that the motility related to DVM
is driven by physiological controls such as phototaxis or
geotaxis, and timed by an endogenous clock (Kohata and
Watanabe, 1986; Wada et al., 1986; Roenneberg et al.,
1989; Eggersdorfer and Ha¨der, 1991; Kamykowski et al.,
1999; Lebert and Ha¨der, 1999), while being influenced by
temperature (Heaney and Eppley, 1980), salinity (Erga
et al., 2003; Bearon et al., 2006; Jephson and Carlsson,
2009), light (Kingston, 1999; Richter et al., 2007) and
nutrient co (...truncated)