Environmental Engineering Reference
In-Depth Information
Temperature and composition
Since sea temperatures govern global biogeographical distributions of
seaweeds any temperature change is expected to affect the distribution range
and seasonality of seaweeds (van den Hoek et al. 1990, Adey and Steneck
2001, Schils and Wilson 2006). Predicted increase in global temperature
(IPCC 2007) is likely to have dramatic effects on the structure and function
of ecosystems worldwide (Carlton 2001, Walther et al. 2002). Signifi cant
changes in biogenic habitat structure including increase in monospecifi c
kelp patches, decrease in mixed canopies, and change in fucoid species
were found along a latitudinal gradient in ocean temperature equivalent to
projected temperature increases for the coming 25-50 years in the southwest
coast of Western Australia (Wernberg et al. 2011b).
In recent decades, global climate change (Hansen et al. 2006) has
caused profound biological changes across the planet (Walther et al. 2002,
Wernberg et al. 2011a). For example, the rockweed beds of southwestern
Nova Scotia, which have been almost 99% pure
Ascophyllum nodosum
with
a minor component of
Fucus vesiculosus
are undergoing a steady increase in
F. vesiculosus
since 2004 in coincidence with an increase in surface seawater
temperature in the maritime region since 2000 (Ugarte et al
.
2009). Along the
Korean Peninsula,
Sargassum
,
Laminaria
and
Ecklonia
forests were abundant
until the end of 1980 but since the beginning of 1990s, these forests had
been decreasing due to various reasons including global warming (Kang
2010).
The impact of the rising temperature on other links in the food web also
affects indirectly the composition of seaweed community. In Tasmania the
strengthening of the East Australia Current (Ridgway 2007) and warming
ocean temperatures, resulting in ocean temperatures exceeding the threshold
for successful reproduction of the herbivorous sea urchin
Centrostephanus
rodgersii
, has facilitated the poleward expansion of their populations (Ling
et al. 2008). As a result, subtidal reefs that formerly supported dense stands
of macroalgae have been intensively grazed and transformed into urchin
barrens, with considerable loss of biological diversity (Johnson et al. 2005,
Ling 2008, Ling and Johnson 2009).
Climatic warming on the time scale of decades may also alter the
composition of the resident biota by facilitating the poleward spread of
species characteristic of warmer temperature regimes (Southward et al. 1995,
Holbrook et al. 1997, Sagarin et al. 1999). Since seaweeds are sedentary, they
are incapable of a rapid response to climate variation by altering the pattern
of individuals' movements; however, changes in distribution would occur
at the level of the population through changes in the ratios of extinction
to colonization at the northern and southern boundaries of the range. For
these species, responses to the warming trend should be slower, refl ected
