Biology Reference
In-Depth Information
water temperature in winter (Bla
ˇ
ina et al.
2009
). By this increased low-temperature
tolerance, this species can successfully survive the winter without visible necrotic
parts or chilling injuries. (3) As thermal stress disrupts the cellular homeostasis of
cells and enhances the production of reactive oxygen species, antioxidants are
crucial for increased stress tolerance (Mittler
2002
; see also Chap.
6
by Bischof
and Rautenberger). Coll
´
n et al. (
2007
) investigated the effects of heat stress on the
transcriptome of
Chondrus crispus
using cDNA microarrays. They showed that
high-temperature stress caused large changes in gene expression and resource
allocation, including antioxidant proteins and detoxifying enzymes. (4) Compatible
solutes are accumulated, which are low-molecular-mass, highly soluble organic
compounds and are particularly known to serve as osmolytes in salt-stressed cells,
including seaweeds (Yancey
2005
). The metabolites in seaweeds can include
betaines, polyols, and sugars, such as mannitol and trehalose, and amino acids,
such as proline (Kirst
1990
; see also Chap.
5
by Karsten). Compatible solutes are
known to exert multiple protective functions in the metabolism and can also act as
antioxidants and can stabilize proteins upon heat stress. Even though similar physi-
ological functions are reasonable to assume in seaweeds as well, they are still to be
experimentally proven (Eggert and Karsten
2010
).
3.5 Temperature Control of Biogeographical Distribution
Boundaries
Geographical distributions of seaweeds are typically delimited at certain seawater
isotherms. Based on the historical concept of Setchell (
1920
) and modified by
Luning (
1990
), local winter and summer isotherms (i.e., long-term mean monthly
temperatures of February and August, respectively) of sea surface temperatures are
used for delimitation of biogeographical regions. Seven biogeographical regions
are typically recognized in marine phycogeography (for details, see Chap.
18
by
Bartsch et al.).
According to van den Hoek (
1982a
,
b
) and Breeman (
1988
), three fundamentally
different types of geographic seaweed boundaries can be distinguished: (1) lethal
boundaries, i.e., high or low temperatures prevent survival of the hardiest life
history stage, (2) reproduction boundaries, i.e., high or low temperatures prevent
completion of the life history, (3) growth boundaries, i.e., temperature requirements
for sufficient increase of population size. Lethal boundaries are determined by the
capacity of the species to survive during the unfavorable season. More specifically,
southern lethal temperature boundaries of cold-adapted species (of the Northern
hemisphere) are set at the August isotherm of the seawater and the northern lethal
limit of warm-adapted species (of the Northern Hemisphere) at the February
isotherm. Temperature limits for growth or reproduction operate during the favor-
able season. Accordingly, southern growth/reproduction limits in the Northern
Hemisphere are set at
the February isotherm and northern boundaries are
