Biology Reference
In-Depth Information
shift in phytoplankton biomass, in zooplankton community structure, and expected
effects on higher trophic levels (Schofield et al.
2010
).
18.3.4.2 Temperate Regions
2
C has been documented in many
cold- and warm-temperate regions (see Sect.
18.1
). At many temperate European
coastlines, migrational shifts of benthic and pelagial species have already taken
place (e.g., benthos overview: Mieszkowska et al.
2006
; Hawkins et al.
2008
;
plankton: Beaugrand and Reid
2003
; fish: Rijnsdorp et al.
2009
). Climate driven
biomass changes or loss of kelp vegetation has recently been reported from many
local sites worldwide (e.g., Japan: Kirihara et al.
2006
, Tasmania: Johnson et al.
2011
, Norway: Andersen et al.
2011
, Spain: D´ez et al.
2012
). In contrast, no
evidence for broadscale latitudinal shifts of kelps since 1850 was found in the
transition region between the boreal and sub-arctic region in the NW-Atlantic
(Merzouk and Johnson
2011
). A recent investigation into the decline of the sugar
kelp
Saccharina latissima
along southern Norwegian shorelines (Andersen et al.
2011
) provides a good example for the complex interactions in the field. After
transplantation of
S. latissima
from healthy to impacted sites, normal growth and
maturation took place in winter and spring, but heavy fouling of epiphytes occurred
over summer followed by mortality. Although duration of periods with summer
temperatures
Within the last decades, an increase in SSTs of
>
20
C increased in recent years, a temperature which is sublethal for
S. latissima
(Bolton and L
>
uning
1982
), mortality could not unequivocally be
correlated to high summer temperatures alone. Instead, Andersen et al. (
2011
)
assumed a cascade of reduced growth at sublethal temperatures, followed by
heavy epiphytism at locations with low wave activity leading to shading, thereby
causing a negative carbon balance and brittleness of thalli and finally mortality—all
factors together possibly preventing recruitment and recovery of the species at the
impacted sites. Successful recruitment is crucial for the continuous recovery of
boundary populations which becomes impacted if the environmental pressure
surpasses critical limits. Within a few years of unfavorable abiotic conditions, the
reproductive capacity was dramatically reduced in southern European marginal
populations of the intertidal brown alga
Fucus serratus
(Viejo et al.
2011
).
Similarly, along the SST gradient in western Australia density of kelp recruits
was inversely related to increasing mean ocean temperature, suggesting an effect
of temperatures on either reproduction or recruits (Wernberg et al.
2010
).
There are a few long-term case studies from temperate coastal regions
investigating possible ecological consequences of environmental warming for
rocky shore communities. Three examples are given here. A 10-year thermal outfall
of a power station which induced a long-lasting SST increase by up to 3.5
C
resulted in a complete change of the intertidal rocky shore community structure
at Diablo Potter Cove in California. The initial dense cover of foliose algae was
replaced by bare rocks, algal crusts, or turf algae and there was a major replacement
of species and decrease of algal richness (Schiel et al.
2004
). A mean SST increase
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