Biology Reference
In-Depth Information
13.5
Impact of Global Climate Changes on Seaweeds
and Their Communities
As stratospheric ozone depletion is highest in polar regions, numerous studies were
performed on the effect of enhanced UV radiation (UVR) on seaweeds from the
Arctic and Antarctic (see Chap.
20
by Bischof and Steinhoff; Karsten et al.
2011
).
The most UV-susceptible stages in the life history of seaweeds are their spores
(Roleda et al.
2007
). Spores of shallow water species exhibit a high UV tolerance,
whereas spores of mid- and lower sublittoral species are increasingly UV suscepti-
ble (Wiencke et al.
2006
). Tolerance of spores to UVR is a major if not one of the
most important factors determining the upper depth distribution limit of kelps and
kelp-like species. Enhanced UVR due to stratospheric ozone depletion may lead to
changes in the depth distribution of seaweeds which may cause significant
snowballing effects.
As temperature is one of the most important factors controlling biogeographic
distribution of seaweeds, distributional shifts are an inevitable effect of global
warming, especially in polar and cold-temperate regions (see Chap.
18
by Bartsch
et al.). Modeled temperature changes through the end of twenty-first century
indicate that North Atlantic-polar to cold-temperate seaweeds will extend their
range into the high Arctic, but retreat along the northeastern Atlantic coasts. In
contrast, many Antarctic seaweeds will presumably not strongly alter latitudinal
distributions due to changes in temperature (M
uller et al.
2011
). Clearly, the
distributional changes of key species as so-called ecological engineers will provoke
substantial and cascading effects in polar and cold-temperate transition areas with
strong consequences for biodiversity and ecosystem functioning.
Although increasing temperatures due to climate change may not affect the
latitudinal distribution of Antarctic seaweeds directly, it very likely is doing so
indirectly via changes in sea-ice extent and duration, particularly along the southern
portion of the western Antarctic Peninsula. Sea-ice cover in this region has been
dramatically changed by increases in air temperatures over the past 30 years,
advancing nearly 2 months later in winter and retreating approximately 1 month
earlier in spring (Smith and Stammerjohn
2001
; Stammerjohn et al.
2008
). These
changes are likely to continue and are thought to be significantly impacting marine
communities (Clarke et al.
2007
; Ducklow et al.
2007
; McClintock et al.
2008
).
The marked decrease in seaweed biomass and species richness historically
observed along the southern portion of the Antarctic Peninsula is thought to be a
result of the increasing sea-ice coverage as one moves south. It seems likely that
seaweed communities typical of the northern portion of the western Antarctic
Peninsula are expanding southward. Unfortunately, seaweed floras in the area
between Anvers and Adelaide Islands (64
S-67
35
0
S) are very poorly studied,
both historically and currently, so the extent to which such changes have and are
occurring is unknown.
Polar regions are not only affected by stratospheric ozone depletion and global
warming, but certainly also threatened by ocean acidification as a result of human
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