Biology Reference
In-Depth Information
century (Johannessen et al.
2004
). In the Antarctic, 87% of the glaciers of the West
Antarctic Peninsula are retreating (Cook et al.
2005
), the ice season has shortened
by about 90 days, and perennial ice does not occur any more at this location
(Martinson et al.
2008
; Stammerjohn et al.
2008
). In the Arctic, oceanic warming
leads to a retreat of the pack-ice border coinciding with the 1
C summer isotherm.
This will provide new habitats for algal colonization in the Arctic and Antarctic
along rocky coastlines (Fig.
18.1
;Muller et al.
2009
,
2011
). As ice-related pressures
on shallow water biota of the Arctic and Antarctic will be reduced, perennial
macroalgae, which are so far restricted mainly to the sublittoral, will be able to
colonize the eulittoral, resulting in an increase in biomass and diversity (Weslawski
et al.
2010
,
2011
). On the other hand, prolonged inflow of glacial melt water will
reduce salinity and increase turbidity of the water due to a higher sediment impact
(Campana et al.
2011
). The concomitant reduction of the euphotic region will
change production rates (Pivovarov et al.
2003
; Deregibus et al. personal commu-
nication; Spurkland and Iken
2011
) and probably will cause an upward shift of the
depth limit of seaweeds. Biomass and seaweed cover already increased between
1988 and 2008 in the rocky littoral of Sorkappland (Svalbard; Weslawski et al.
2010
) in the Arctic accompanied by an increase in air temperature and SST and a
marked decrease in the duration and extent of sea-ice cover. However, no “new”
species were detected but are expected in future (M
uller et al.
2009
). The described
upward shift of seaweeds might though be counteracted by high levels of ultraviolet-
B radiation (UVBR) due to stratospheric ozone depletion (Weatherhead and
Andersen
2006
; Zacher et al.
2011
) which still prevails in the Arctic and Antarctica.
UVBR is one of the most important factors controlling the upper depth distribution
of seaweeds. Effects have been demonstrated from the cellular to the ecosystem
level, affecting community structure and diversity in the Arctic and Antarctic
(Bischof et al.
2006
; Zacher et al.
2007
; Campana et al.
2011
; Karsten et al.
2011
;
Fricke et al.
2011
; see Chap.
20
by Bischof and Steinhoff). UVBR, turbidity, water
temperature, and sea-ice conditions are interdependent factors but multifactorial
interactive effects on polar biota have scarcely been investigated (Muller et al.
2008
;
Fredersdorf et al.
2009
). Bifactorial experiments on Arctic kelp species indicated
that negative effects of UVBR can be mitigated by the interaction with increased
temperature. For example, germination of zoospores of the kelp
Laminaria digitata
was inhibited almost completely by UVBR at 2
C, but not at 7
C(M
€
uller et al.
€
2008
).
Compared to changes in the Arctic, the distributional changes of seaweeds in the
Antarctic will probably be minor (M
uller et al.
2009
,
2011
) as the model data predict
an SST increase of only 1
C throughout the year in the Antarctic region. Moreover,
only few cold-temperate species will be able to colonize present-day Antarctic
coasts. One example might be the brown alga
Chordaria linearis
, which has been
found already on two locations in West Antarctica (M
€
uller et al.
2009
,
2011
). The
estimation of minor changes for seaweed richness along the coastal West Antarctica
Peninsula under climate change conditions contrasts to demonstrated changes in the
respective pelagic ecosystem in response to rapid climate changes, which include a
€
