Seaweed Acclimation to Salinity and Desiccation Stress - Seaweed Biology - page 88

5.2.1 Rate of Survival

The rate of survival can be easily estimated by following seaweed growth or
photosynthesis activity under defined stress conditions, or using classical vital
staining techniques for individual cells such as Evans Blue (Russell 1985 ; Thomas
and Kirst 1991 ). Only dead cells with damaged membranes will take up this stain
and hence appear blue under the microscope. These days a range of commercially
available fluorescence dyes such as the so-called Live-Dead kits are available
which in combination with an epifluorescence microscope allow the evaluation
and visualization of even smallest damages on membrane integrity.
The available data on cell viability in relation to salinity indicate that members
of eulittoral green algal genera such as Ulva (incl. Enteromorpha ), Acrosiphonia ,
UIothrix, Cladophora , and Prasiola are generally much less affected than sublitto-
ral red and brown seaweeds (Russell 1985 , 1987 , Kain and Norton 1990 ; Thomas
and Kirst 1991 ; Karsten et al. 1991a ). While even under triple seawater concentra-
tion 75% of green algal cells remain intact, mortality in sublittoral brown algae

such as Phaeurus antarcticus increased to almost 100% (Karsten et al. 1991a ). This
rather euryhaline feature of eulittoral green seaweeds may be considered as impor-
tant environmental factor for controlling vertical species zonation on the shore
(Russell 1987 ).

>

5.2.2 Growth

From an ecological perspective, growth represents the most relevant physiological
process to describe the performance of seaweeds in their respective habitat because
it optimally integrates all positive and negative environmental effects on the
organism and hence reflects the acclimation potential (Gustavs et al. 2009 ). A
careful analysis of growth patterns allows the evaluation of salinity tolerance limits,
growth optima, and acclimation abilities of individual seaweed species, and, thus
facilitates the interpretation of natural distributions. Knowledge of physiological
limits is necessary to estimate and understand distribution limits within an unknown
community, i.e., in a competitive situation. Additionally, the shape of the growth
rate curve in dependence of any abiotic factor characterizes a seaweed species as
steno- or euryoecious, or in case of salinity as steno- or euryhaline, which defini-
tively affects its competitive strength.
Until now, numerous ecophysiological studies have been undertaken on the
salinity effects on growth in seaweeds (Jacob et al. 1991 ; Karsten et al. 1991a ,
1993b , 1994 , 1996b ; Karsten and West 1993 ; Kirst 1990 and references therein,
Thomas and Kirst 1991 ). All these papers clearly indicate that eulittoral seaweeds
from polar to tropical regions grow between low salinities (5-10 S A ) and double
seawater concentration (66-68 S A ), in most cases with conspicuous optima under
normal seawater conditions. The supralittoral Prasiola crispa ssp. antarctica even