20
characteristic of the spring and early summer, when sea ice breakage causes a
deeper penetration of irradiance into the highly transparent Antarctic coastal waters.
Flores-Molina et al. (2016) showed that tolerance to UV radiation and temperature
is dependent on high concentrations of constitutive soluble phlorotannins with
UV-absorbing properties (Gómez and Huovinen 2015). Increased soluble/nonsoluble and constitutive/inducible phlorotannin concentrations under high UV
stress lessen the normal inhibition of the photosynthetic system and DNA damage,
as has been demonstrated in several brown algae (e.g., Swanson and Druehl 2002).
Two sibling brown algae species, Lessonia berteroana and L. spicata, are distributed along the Chilean coast in two contiguous biogeographic regions, between
18°S and 30°S and between 29°S and 41°S, respectively. These species evidence
contrasting regimes of air exposure during high tide and differential stress tolerance
capacities. For example, post-germination development in L. spicata, which thrives
in the southern biogeographic region and is exposed to milder emersion regimes,
abruptly stopped after 1 or 2 h of daily desiccation treatments (López-Cristoffanini
et al. 2013). In contrast, 75% of germinated L. berteroana spores developed into
gametophytes despite 1 h of daily desiccation treatment, and 50% continued development even with 2 h of daily desiccation. First, this indicates that desiccation stress
is a selective force able to explain the disjunctive distribution between the less tolerant species of the lower intertidal zone along the Chilean coast. Secondly, this also
supports that L. berteroana evolved greater desiccation tolerance than L. spicata to
successfully recruit and develop along the drier intertidal shores of northern Chile.
Recent research by Contreras-Porcia et al. (unpublished) evaluated if tolerance
mechanisms to desiccation stress present different capacities in Porphyra and
Pyropia spp. along Chilean shores spanning the previously mentioned biogeographic zone (18°S–41°S). Higher levels of protein and lipid oxidation were measured in Porphyra and Pyropia spp. from northern Chilean shores, confirming that
more extreme emersion regimes with higher desiccation stress prevail in this region.
However, no significant differences were found between species and latitude in
regard to the activation of antioxidant enzymes under desiccation stress. Indeed, all
Porphyra and Pyropia spp. showed a similarly adaptive and plastic regulation of
these enzymes under natural and in vitro desiccation (Fig. 2.1). Therefore, for algae
species thriving in the upper intertidal zone, different environmental factors could
elucidate disjunctive distributional ranges along the Chilean shoreline.
2.1.5 Perspectives
Considering the prior information, we can conclude that there is a general lack of
studies investigating causal relationships between geographical distribution and the
physiological tolerances of seaweeds to diverse environmental abiotic factors.
Moreover, despite the discoveries of specific tolerance mechanisms under a number of
stressful conditions, few researchers have synchronously compared the roles of these
mechanisms with specific regulations under different abiotic stressors. This highlights
the necessity to further investigate and compare the ecophysiological similarities and
L. Contreras-Porcia et al.
characteristic of the spring and early summer, when sea ice breakage causes a
deeper penetration of irradiance into the highly transparent Antarctic coastal waters.
Flores-Molina et al. (2016) showed that tolerance to UV radiation and temperature
is dependent on high concentrations of constitutive soluble phlorotannins with
UV-absorbing properties (Gómez and Huovinen 2015). Increased soluble/nonsoluble and constitutive/inducible phlorotannin concentrations under high UV
stress lessen the normal inhibition of the photosynthetic system and DNA damage,
as has been demonstrated in several brown algae (e.g., Swanson and Druehl 2002).
Two sibling brown algae species, Lessonia berteroana and L. spicata, are distributed along the Chilean coast in two contiguous biogeographic regions, between
18°S and 30°S and between 29°S and 41°S, respectively. These species evidence
contrasting regimes of air exposure during high tide and differential stress tolerance
capacities. For example, post-germination development in L. spicata, which thrives
in the southern biogeographic region and is exposed to milder emersion regimes,
abruptly stopped after 1 or 2 h of daily desiccation treatments (López-Cristoffanini
et al. 2013). In contrast, 75% of germinated L. berteroana spores developed into
gametophytes despite 1 h of daily desiccation treatment, and 50% continued development even with 2 h of daily desiccation. First, this indicates that desiccation stress
is a selective force able to explain the disjunctive distribution between the less tolerant species of the lower intertidal zone along the Chilean coast. Secondly, this also
supports that L. berteroana evolved greater desiccation tolerance than L. spicata to
successfully recruit and develop along the drier intertidal shores of northern Chile.
Recent research by Contreras-Porcia et al. (unpublished) evaluated if tolerance
mechanisms to desiccation stress present different capacities in Porphyra and
Pyropia spp. along Chilean shores spanning the previously mentioned biogeographic zone (18°S–41°S). Higher levels of protein and lipid oxidation were measured in Porphyra and Pyropia spp. from northern Chilean shores, confirming that
more extreme emersion regimes with higher desiccation stress prevail in this region.
However, no significant differences were found between species and latitude in
regard to the activation of antioxidant enzymes under desiccation stress. Indeed, all
Porphyra and Pyropia spp. showed a similarly adaptive and plastic regulation of
these enzymes under natural and in vitro desiccation (Fig. 2.1). Therefore, for algae
species thriving in the upper intertidal zone, different environmental factors could
elucidate disjunctive distributional ranges along the Chilean shoreline.
2.1.5 Perspectives
Considering the prior information, we can conclude that there is a general lack of
studies investigating causal relationships between geographical distribution and the
physiological tolerances of seaweeds to diverse environmental abiotic factors.
Moreover, despite the discoveries of specific tolerance mechanisms under a number of
stressful conditions, few researchers have synchronously compared the roles of these
mechanisms with specific regulations under different abiotic stressors. This highlights
the necessity to further investigate and compare the ecophysiological similarities and
L. Contreras-Porcia et al.