Biology Reference
In-Depth Information
2. Within one species, juvenile and smaller specimens are generally more vulnera-
ble than adult and larger algae. The reproductive microstages are more suscepti-
ble than adult sporophytes and acclimation to UVB exposure is possible, to at
least some extent, for most of the species investigated so far (Dring et al.
1996
;
Roleda et al.
2007
).
3. Phylogenetically old organismic groups, like algae, have evolved under
conditions with much higher UVB irradiances in the atmosphere than nowadays,
even under conditions of severe ozone depletion. Thus, most organisms have
developed some kind of strategies to cope with the adverse effects of UVB
exposure, which can be summarized by the terms: avoidance, protection, and
repair (see Bischof et al.
2006a
).
4. UVR may also confer promoting effects, like, e.g., the induction of photorepair
processes (Hanelt and Roleda
2009
).
20.2 Species-Dependent UV Susceptibility Based on Latitudinal
and Depth Distribution: The Frame Set by Adaptation
The frame of species-dependent reactions of seaweeds to UVB exposure is set by
genetically fixed adaptation. Early laboratory studies on Antarctic seaweeds, which
were kept in stock cultures for more than 10 years still revealed distinct species-
specific reaction patterns toward UV exposure once they were grown to macrothalli
and exposed to identical UV conditions (Bischof et al.
1998a
). Thus, it was
confirmed that shallow water species, like the two green algae
Enteromorpha
bulbosa
(now termed
Ulva bulbosa,
also referred to as
U. hookeriana
) and
Acrosiphonia arcta,
were still extremely UV tolerant even after long-term exposure
to dim light conditions in stock cultures. In contrast, photosynthesis of the red algal
species,
Phycodrys austrogeorgica
and
Delesseria lancifolia,
responded extremely
sensitive toward UV exposure. Overall, the general zonation patterns seaweeds
display, e.g., at the islands off the Antarctic Peninsula are reflected by their UV
sensitivity even decades after their isolation from the field (Bischof et al.
1998a
).
The same adaptational setting has been observed in six red algal species from
cold-temperate regions and with different zonation patterns with respect to their
species-specific growth rates and ability to cope with UVB-mediated DNA damage
(van de Poll et al.
2001
). Again, these algae were cultivated under identical culture
conditions and exposed to similar irradiance of UVB and, evidently, the respective
inhibition of growth was in line with the species position on the shore, with the two
shallow water species (
Palmaria palmata
and
Chondrus crispus
) hardly exhibiting
inhibition in growth, whereas in deep-water algae (
Phycodrys rubens
and
Polyneura hilliae)
growth was inhibited almost completely. Furthermore, accumu-
lation of damaged DNA, expressed as thymine dimer formation, was found in the
two deep-water species, which apparently lack the ability for sufficient DNA repair.
This confirms the strong adaptation of these species to their low irradiance
