Biology Reference
In-Depth Information
Phaeophyceae is caused by light absorption of the carotenoid fucoxanthin, and the
red color of the Rhodophyceae by the phycobiliproteins. If the LHC consists mainly
of chlorophylls, the color is green, as is typical for the Chlorophyceae. The different
absorption characteristics of the respective LHC correspond to different underwater
light spectra. Different light qualities occur within the water body by absorption
and scattering of light (Jerlov
1976
) especially with increasing water depth and/or
turbidity. Generally, the blue-green waveband penetrates deepest into the water
body as the shorter and longer wavelength are more absorbed by the water
molecules or scattered by particles. Photosynthetic apparatus of algae has adapted
to these different wavebands. The occurrence of the various types of pigments in the
LHC and their arrangement in both photosystems are responsible for different
photosynthetic efficiencies of different spectral wavebands which affect photosyn-
thetic activity. The action spectrum of photosynthesis of red algae shows a so-called
blue and red drop, first described by Haxo and Blinks (
1950
). Green light is best
absorbed by the phycobilines so it shows the highest photosynthetic rates in red
algae. In contrast blue and red/far red light does not induce high electron transport
rates because chlorophyll molecules act as the main antenna pigment in photo-
system I so that the reaction center of PS I is primarily activated (Butler
1978
). Blue
and far red light induces principally charge separation in the reaction center of PS I
and cyclic electron transport around PS I. As charge separation of PS II in red algae
is not induced to an equal amount, linear electron transport rate is small and oxygen
production rate is low (Haxo and Blinks
1950
; Hanelt et al.
1992
).
Engelmann (
1883
,
1884
) pointed to the fact that most green algal species occur
in the eulittoral and upper sublittoral, whereas brown algae grow often in deeper
zones and many red algae can be characterized as deep water species. In deep water,
where blue-green light prevails, the red pigments of the Rhodophyceae allow
an efficient absorption (Biebl
1962
). However, this is only partly valid because
the absorption characteristic depends also on several other factors, especially the
thallus morphology. It applies more to coastal waters than to oceanic waters
(Larkum et al.
1967
). If the algal thallus is thick enough it appears nearly black
and absorbs light over the whole spectral range, as typical for brown kelps (Luning
1990
). In addition accessory pigments do enhance light absorption in the blue-green
range and examples of green algae growing in deep waters are not rare (Dring
1981
,
1982
; Ramus
1981
). Anyhow, the deepest algae found are crustose red algae with a
quite low light demand (Littler et al.
1986
), which is not only due to their low
growth rate and special morphology (one absorption layer) but also due to their
capability to use the impinging photons very efficiently in the blue-green wave-
length range (Hanelt et al.
2003
). In vivo absorptance of thin and thick algal thalli of
the different pigment groups was investigated by L
uning and Dring (
1985
). Their
study demonstrated that a good correlation exists between spectral thallus absorp-
tion and action spectrum of photosynthesis, as well as a greater thallus thickness
supports photosynthetic activity also when wavebands are slightly absorbed.
Leukart and L
€
uning (
1994
) demonstrated in several red algal species that growth
rate and photosynthesis depends on the light quality during culture and on the
pigment content under these conditions. The light requirements were lowest in
€
