Light is primarily used as a source of energy, enabling organisms to adapt to a steadily changing environment.
The utilization of light by an organism is regulated by a process known as photoacclimation, or chromatic adaptation, including mechanisms to avoid an excess of light energy, such as photoprotection (Falkowski and La Roche 1991) and mechanisms to take advantage of low irradiances in any given ambient lighting. Light can also be used as an environmental signal to control metabolic and reproductive processes (Rüdiger and Figueroa 1992).
Monochromatic light can provide the signalling necessary to regulate algal metabolism, reproduction and growth (Dring 1988), prompting, in turn, a variety of photomorphogenetic strategies, such as the control of cell growth or induced enzymatic activation (Lüning 1992). Additionally, light can induce shade-avoiding plasticity (Monro and Poore 2005).
Marine red algae occur in environments subjected to wide variations of irradiance and spectral distribution, and their pigment contents are regulated by irradianceand light qualities.
These responses may be the result of photomorphogenetic signalling processes with photoreceptor control that regulate growth and metabolism (Talarico and Maranzana 2000).
Photosynthetic changes can result from an imbalance of photosystems, a difference in the rate at which photosystems
turn over, a deficiency in the electron transport chain, or a major change in the spatial relationship between the two photosystem (Gantt 1990).