19
Global ecological research of intertidal zonation patterns for Pyropia and
Porphyra suggests that these species seasonally or annually change in regard to relative abundances and distributions along intertidal levels within and across sites.
These distributional patterns would be caused not by adaptations to intertidal fringes
per se, but by adaptations to abiotic factors inducing physiological stress during high
tide emersion, which are highly variable over space and time. For example, West
et al. (2005) used molecular tools to identify Pyropia and Porphyra species and
described the intertidal distributions of these genera at two sites from the New
England coast (USA). At the first site, Fort Stark, the upper intertidal zone was dominated over the year by Porphyra umbilicalis, with the mean biomass of this alga
peaking during the summer. In the lower intertidal zone, Po. umbilicalis and Pyropia
leucosticta were most conspicuous and showed maximum biomasses and coverage
percentages in the summer. In contrast, no species occurred during winter in the
lower intertidal zone at Fort Stark. At the second site, Dover Point, Po. umbilicalis
was restricted to the upper intertidal zone where, together with Po. purpurea, this
was the dominant species for the majority of seasons. However, during winter and
early spring Pyropia yezoensis was the most abundant algal species in the upper
intertidal zone of Dover Point. Using the above examples, it is possible to infer that:
(1) the range of tidal levels occupied by a specific species, such as Po. umbilicalis,
can change across sites (Fort Stark vs Dover Point), and (2) across seasons (summer
vs winter) the same species, such as Po. umbilicalis and Py. leucosticta at Fort Stark,
can show contrasting patterns of occurrence, biomass, and coverage percentage
within the same intertidal level.
As a result of varied specializations, research on the ecophysiological performance and distribution of different foliose Bangiales species requires significant
changes in the sampling design. Modifications are needed since environmental factors, such as temperature, UV and PAR radiation, and relative humidity, do not
always coincide with tidal fringes and usually fluctuate on smaller spatial scales due
in part to topographical irregularities of the intertidal landscape and, on larger
scales, due to climatic and oceanographic variations. Therefore, updated sampling
models will need to (1) more finely measure important stress factors to define intertidal areas with similar abiotic conditions and (2) compare the likely expansion or
shrinkage of algal patches seasonally and yearly.
2.1.4 Differential Tolerances to Emersion Stressors
and the Geographic Distribution of Seaweeds
Across Intertidal Shores
Depending on the seaweed species, tolerances to different abiotic stressors can
likely explain distribution ranges across biogeographic zones. For example, the
endemic Antarctic brown alga Desmarestia anceps (Desmarestiales) flourishes
most of the year in the more stable and nutrient-rich lower subtidal zone (>5 m
deep). Nevertheless, this alga is also adapted to grow under the high UV radiation
2 Tolerance Pathways to Desiccation Stress in Seaweeds
Global ecological research of intertidal zonation patterns for Pyropia and
Porphyra suggests that these species seasonally or annually change in regard to relative abundances and distributions along intertidal levels within and across sites.
These distributional patterns would be caused not by adaptations to intertidal fringes
per se, but by adaptations to abiotic factors inducing physiological stress during high
tide emersion, which are highly variable over space and time. For example, West
et al. (2005) used molecular tools to identify Pyropia and Porphyra species and
described the intertidal distributions of these genera at two sites from the New
England coast (USA). At the first site, Fort Stark, the upper intertidal zone was dominated over the year by Porphyra umbilicalis, with the mean biomass of this alga
peaking during the summer. In the lower intertidal zone, Po. umbilicalis and Pyropia
leucosticta were most conspicuous and showed maximum biomasses and coverage
percentages in the summer. In contrast, no species occurred during winter in the
lower intertidal zone at Fort Stark. At the second site, Dover Point, Po. umbilicalis
was restricted to the upper intertidal zone where, together with Po. purpurea, this
was the dominant species for the majority of seasons. However, during winter and
early spring Pyropia yezoensis was the most abundant algal species in the upper
intertidal zone of Dover Point. Using the above examples, it is possible to infer that:
(1) the range of tidal levels occupied by a specific species, such as Po. umbilicalis,
can change across sites (Fort Stark vs Dover Point), and (2) across seasons (summer
vs winter) the same species, such as Po. umbilicalis and Py. leucosticta at Fort Stark,
can show contrasting patterns of occurrence, biomass, and coverage percentage
within the same intertidal level.
As a result of varied specializations, research on the ecophysiological performance and distribution of different foliose Bangiales species requires significant
changes in the sampling design. Modifications are needed since environmental factors, such as temperature, UV and PAR radiation, and relative humidity, do not
always coincide with tidal fringes and usually fluctuate on smaller spatial scales due
in part to topographical irregularities of the intertidal landscape and, on larger
scales, due to climatic and oceanographic variations. Therefore, updated sampling
models will need to (1) more finely measure important stress factors to define intertidal areas with similar abiotic conditions and (2) compare the likely expansion or
shrinkage of algal patches seasonally and yearly.
2.1.4 Differential Tolerances to Emersion Stressors
and the Geographic Distribution of Seaweeds
Across Intertidal Shores
Depending on the seaweed species, tolerances to different abiotic stressors can
likely explain distribution ranges across biogeographic zones. For example, the
endemic Antarctic brown alga Desmarestia anceps (Desmarestiales) flourishes
most of the year in the more stable and nutrient-rich lower subtidal zone (>5 m
deep). Nevertheless, this alga is also adapted to grow under the high UV radiation
2 Tolerance Pathways to Desiccation Stress in Seaweeds