Impacts of Stratospheric Ozone Depletion and Solar UVB Radiation on Seaweeds - Seaweed Biology

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environment at their natural growth site. Furthermore, the accumulation of DNA

damage in seaweeds can be regarded as a very good measure for the degree of

adaptation of a given species towards UVB exposure (van de Poll et al. 2001 ).

These findings were also confirmed in a transplantation experiment on another

deep-water red algal species Delesseria sanguinea , in which growth was also

impaired when the alga was exposed to surface solar radiation (Pang et al. 2001 ).

Results obtained indicated the absence of any protecting mechanisms against

excessive radiation in this algal species, which are, however, not relevant to the

species as it inhabits the low light environments in the shade of canopy algae or in

great water depths. Thus, sublittoral seaweeds may avoid being exposed to UVB

simply by growing in water depths, in which most of the UVB irradiance is already

attenuated by the water column above. A prominent example of this avoidance

strategy is also the Arctic endemic deep-water kelp Laminaria solidungula (Brey

2009 ). Other algal species following this strategy may also be growing in the

understory being protected by the algae above or following a cryptic life cycle.

Generally, all modulation of ecophysiological reactions toward variation in

abiotic factors is conditioned by genetic adaptation. This is also visible in two red

algal species from Spitsbergen (Arctic) with slightly different vertical zonation

preferences (Karsten et al. 1999 ): Devaleraea ramentacea as a species from

shallow waters is permanently equipped with high activities of reactive oxygen

scavenging superoxide dismutase (SOD, see Chap. 6 by Bischof and Rautenberger).

This high but static activity is reasonable for a species from shallow waters, where

usually strong variation in abiotic conditions and, thus, the onset of stressful

conditions to photosynthesis potentially resulting in increased ROS production is

more likely than in more stable deeper waters. However, maintaining a protective

system on such a high level throughout the year is probably energetically cost

intense. Thus, species which are not permanently exposed to stressful conditions,

e.g., in deeper waters, may favor the strategy to rather respond to abiotic stress and

to increase protective strategies, like SOD activity, only when they are needed

during times of, e.g., high UV irradiance. Palmaria palmata inhabiting slightly

deeper waters than D. ramentacea is applying this strategy (Karsten et al. 1999 ;