16
temperature extremes (Chapman 1995; Davison and Pearson 1996), ranging from
the highly tolerant F. spiralis to the less tolerant F. vesiculosus and least tolerant F.
serratus. Chapman (1990) experimentally demonstrated that F. spiralis is excluded
from the midlittoral zone by the competitively superior F. vesiculosus. This suggests
that the range of emersion time tolerated by F. spiralis depends more on tolerance
ranges to abiotic stressors rather than on a specialization and circumscribed exploitation of the drier intertidal zones.
Indeed, most Fucales species do not require periodic drying out, with the exception of Pelvetia canaliculata (Rugg and Norton 1987), a candidate for studying
algal specialization to upper intertidal abiotic stressors. On the other hand, F. vesiculosus from the Baltic Sea, which were introduced to this non-tidal sea approximately 7,500 years ago, evidence lesser desiccation stress tolerance to experimental
emersion than close relatives from the North Sea. As demonstrated by Pearson et al.
(2000), the photoprotective processes of Baltic Sea algae are rapidly impaired during desiccation stress at or below 10% water content, and photosynthetic activity is
not as rapidly or as completely recovered as North Sea F. vesiculosus specimens.
This differentiated tolerance could be the result of interactions between desiccation
and temperature or between desiccation tolerance and salinity.
Abe et al. (2001) measured changes in water potential and photosynthetic activity during dehydration and rehydration for 18 algal species from the upper, mid, and
lower intertidal zones along the southwest Pacific shoreline of Shimoda, Japan.
These researchers evaluated the water potential, in addition to water content, as a
reliable indicator of the thermodynamic state of cellular water content and degree of
desiccation. It was found that Porphyra dentata (Bangiales), an upper intertidal species, is able to tolerate a water potential as low as -158 MPa (i.e., 2% water content
with 30% relative air humidity), with the photosynthetic apparatus of this alga still
in motion. Moreover, the photosynthetic activity of Po. dentata completely recovered after rehydration, showing a superior desiccation tolerance capacity than species occurring in lower intertidal zones. In contrast, Chondrus verrucosus
(Gigartinales), Petalonia fascia (Ectocarpales), and Gelidium elegans (Gelidiales),
the least tolerant species of the lower intertidal zone, were injured after reaching
their lowest water potential threshold (−14 MPa). Finally, mid-intertidal species
showed intermediate levels of cellular desiccation tolerance, with water potentials
ranging from −14 to −158 MPa.
Early studies on desiccation stress in macroalgae mainly focused on determining
the minimum cellular water content tolerated by different intertidal species and the
capability of the photosynthetic systems to recover after long exposures to dry air
(e.g., Schonbeck and Norton 1980; Smith et al. 1986; Lipkin et al. 1993; Abe et al.
2001). All of these studies agree that the tolerance or non-tolerance of algae species
to desiccation and, generally to emersion, can be determined by the buffering capacities of each species to the damage produced during this environmentally stressful
condition. Therefore, it is the ability to withstand desiccation stress and quickly
recover during rehydration through buffering mechanisms, and not the ability to retain
cellular water, that characterizes algae able to flourish in the drier intertidal zones.
L. Contreras-Porcia et al.
temperature extremes (Chapman 1995; Davison and Pearson 1996), ranging from
the highly tolerant F. spiralis to the less tolerant F. vesiculosus and least tolerant F.
serratus. Chapman (1990) experimentally demonstrated that F. spiralis is excluded
from the midlittoral zone by the competitively superior F. vesiculosus. This suggests
that the range of emersion time tolerated by F. spiralis depends more on tolerance
ranges to abiotic stressors rather than on a specialization and circumscribed exploitation of the drier intertidal zones.
Indeed, most Fucales species do not require periodic drying out, with the exception of Pelvetia canaliculata (Rugg and Norton 1987), a candidate for studying
algal specialization to upper intertidal abiotic stressors. On the other hand, F. vesiculosus from the Baltic Sea, which were introduced to this non-tidal sea approximately 7,500 years ago, evidence lesser desiccation stress tolerance to experimental
emersion than close relatives from the North Sea. As demonstrated by Pearson et al.
(2000), the photoprotective processes of Baltic Sea algae are rapidly impaired during desiccation stress at or below 10% water content, and photosynthetic activity is
not as rapidly or as completely recovered as North Sea F. vesiculosus specimens.
This differentiated tolerance could be the result of interactions between desiccation
and temperature or between desiccation tolerance and salinity.
Abe et al. (2001) measured changes in water potential and photosynthetic activity during dehydration and rehydration for 18 algal species from the upper, mid, and
lower intertidal zones along the southwest Pacific shoreline of Shimoda, Japan.
These researchers evaluated the water potential, in addition to water content, as a
reliable indicator of the thermodynamic state of cellular water content and degree of
desiccation. It was found that Porphyra dentata (Bangiales), an upper intertidal species, is able to tolerate a water potential as low as -158 MPa (i.e., 2% water content
with 30% relative air humidity), with the photosynthetic apparatus of this alga still
in motion. Moreover, the photosynthetic activity of Po. dentata completely recovered after rehydration, showing a superior desiccation tolerance capacity than species occurring in lower intertidal zones. In contrast, Chondrus verrucosus
(Gigartinales), Petalonia fascia (Ectocarpales), and Gelidium elegans (Gelidiales),
the least tolerant species of the lower intertidal zone, were injured after reaching
their lowest water potential threshold (−14 MPa). Finally, mid-intertidal species
showed intermediate levels of cellular desiccation tolerance, with water potentials
ranging from −14 to −158 MPa.
Early studies on desiccation stress in macroalgae mainly focused on determining
the minimum cellular water content tolerated by different intertidal species and the
capability of the photosynthetic systems to recover after long exposures to dry air
(e.g., Schonbeck and Norton 1980; Smith et al. 1986; Lipkin et al. 1993; Abe et al.
2001). All of these studies agree that the tolerance or non-tolerance of algae species
to desiccation and, generally to emersion, can be determined by the buffering capacities of each species to the damage produced during this environmentally stressful
condition. Therefore, it is the ability to withstand desiccation stress and quickly
recover during rehydration through buffering mechanisms, and not the ability to retain
cellular water, that characterizes algae able to flourish in the drier intertidal zones.
L. Contreras-Porcia et al.