Biology Reference
In-Depth Information
Only in the case of
Desmarestia anceps
from 30 m, a negative C balance was
determined, indicating that at this depth the alga is at its lower distribution limit.
In contrast,
P. decipiens, Gigartina skottsbergii
and
Trematocarpus antarcticus
and especially
Himantothallus grandifolius
are metabolically able to grow even in
deeper waters which mean they have very modest requirements.
Under low light conditions higher pigment content within the thalli was
observed as under strong light conditions (Ramus et al.
1976
,
1977
). The chance
of photon absorption increases with increasing photosynthetic antenna size. Algae
collected from or transplanted to different water depths show that the content of
accessory pigments increases with lower light conditions in deep waters (Luning
1990
), e.g., in green algae the chlorophyll
a:b
ratio decreases demonstrating
especially the increase of the antenna size of the photosynthetic apparatus
(Yokohama and Misonou
1980
). Whereas under low light conditions in deep
water a larger antenna size increases the capacity of light absorption, a smaller
antenna helps to avoid photoinhibition and photodamage due to over excitation
under high light conditions close to the water surface or during emergence at low
tide. Under low light conditions the plant invests more energy in the synthesis of
light-collecting pigments and in strong light into the synthesis of photosynthetic
enzymes, electron chain components as well as photo-protective structures and
energy-dissipating mechanisms.
A study of Marquardt et al. (
2010
) showed that the saturation point
E
k
of all
red algal species tested decreased with increasing depth concomitantly with
the decreasing light availability. This may be due to the adjustment of the photo-
synthetic apparatus itself via changes of the reaction center ratio, changes of the
relative size of the light-harvesting complex (LHC) or changes in the relative
content of light protective pigments. Changes in thallus morphology are another
possibility to achieve acclimation, e.g., change of thickness, branching, length,
density of photosynthetic units (Kuster et al.
2004
). Johansson and Snoeijs (
2002
)
demonstrated by measurements of photosynthesis versus irradiance curves (PE
curves) that light-saturated net photosynthetic rates (
P
max
), respiratory rates in
darkness (
R
d
) and the initial slope (
a
) were strongly related to algal morphology
with generally higher values for thinner species. The compensation irradiance (
E
c
)
and saturating irradiance (
E
k
) were strongly related to water depth with lower
values at higher depth. One advantage of thin sheet-like and filamentous species
is the capability of fast growth, which is coupled to high photosynthetic rates per
unit biomass (Littler et al.
1983
; Falkowski and Raven
1997
), resembling rather the
conditions in shallow waters. In several macroalgae the photosynthetic parameters
P
max
and
are highly dependent on thallus morphology with higher and faster O
2
production rates for thinner and filamentous species, and lower rates for coarser and
thicker species when normalized to biomass (measured as dry weight) and opposite
when normalized to algal surface area (Johansson and Snoeijs
2002
). Similar
relationships were described for five green-algal species by Arnold and Murray
(
1980
) as well as by Littler (
1980
) for 45 species of marine macroalgae from field
incubations. Thus, deeper growing algal species are expected to have lower
E
c
and
a
