spectrum is also observed in nature, particularly with
increasing depth, where corals generally respond to such
changes by modifying the quantity and/or quality of photoprotective pigments and fluorescent proteins (Titlyanov &
Titlyanova 2002). Corals from shallow water tend to be
lighter in colour, and most have UV-absorbing pigments
that tint them with colours such as purple, pink, blue and
green (Delbeek & Sprung 1994; Osingaet al. 2008). This
adaptive response is not immediate, and placing corals that
were adapted to low light, or had been temporarily lightstarved, into a location with high irradiances can induce a
light shock, which may ultimately damage the coral beyond
its capacity to repair itself (Warner et al.1999). D’Angelo
et al.(2008) showed that the molecular response ofAcropora pulchraandA. milleporaafter 8 h of light stimulation
was still lower than a control group of coral exposed to blue
light during 4 weeks. This relatively slow increase in the
genetic expression of corals suggests that the accumulation
of pigments is a medium-/long-term adaptive process. The
production of fluorescent proteins simultaneously provides
the coral with intense colours. Although in these situations
coral health will likely not be optimal, because the coral is
under stress, it will display colours that are more attractive
to humans, thus improving its quality for the MOT. This
approach may be combined with coral stress diagnostic
tools (Kenkel et al.2014) to avoid reaching a point of no
return. Another study investigated the individual and combined effect of blue and red light in coral photophysiology
(Wijgerde et al. 2014). Results of the latter study are in
agreement with previous studies (Kinzieet al.1984; Wang
et al. 2008), demonstrating that blue light (either narrow
bandwidth or as part of a full spectrum) is essential to the
growth of corals and bothin hospite andex hospite Symbiodinium.
As previously mentioned, light quality can also be changed through the use of different light sources. Each type of
lighting has its own advantages and disadvantages. They all
vary in purchase and maintenance cost, light spectrum,
longevity, efficiency and power (Rocha et al.2013a). Metal
halide lamps and fluorescent lighting have been the two
most commonly used types of aquarium lighting (Osinga
et al. 2008), particularly the first, because they closely
resemble the sunlight spectrum. However, for aquaculture
purposes, they are not the most energy-efficient light
source. Fluorescent lights, as well as LEDs, are more efficient in terms of conversion of energy into light and in
addition allow for more flexibility with respect to manipulation of the light quality provided to the corals. Further,
LED light sources provide a larger array of light colours
available to culture corals (Wijgerdeet al.2014). A recent
study investigated the effect of using light-emitting plasma
(LEP) or LED light sources, as well as different irradiances,
on the growth of the stony symbiotic coralGalaxea fascicu