Environmental Engineering Reference
In-Depth Information
community changes such as decreases in the abundance of higher trophic
level species due to changes in ecological interactions and biological
processes (Holbrook et al. 1997, Schiel et al. 2004).
Global warming is expected to result in an acceleration of current
rates of sea level rise, inundating many low-lying coastal and intertidal
areas. Although predictions vary across models and regions, the sea level
is expected to rise 0.18-0.79 m during the 21st century, owing to thermal
expansion and polar ice melt (IPCC 2007). The most obvious consequence
of a rise in sea level will be an upward shift in species distribution. With
the exception of some slow-growing species such as many corals, most
species are expected to be able to keep pace with predicted rates of sea
level rise (Harley et al. 2006). However, decreased habitat availability
within a particular depth zone can lead to striking ecological changes such
as the reduction of the intertidal habitat area where steep topography and
anthropogenic structures (e.g., sea walls) prevent the inland migration of
mudfl ats and sandy beaches (Schlacher et al. 2007). In addition, changes
in sea level will shift the locations of existing anthropogenic structures to
lower positions on the shore, amplifying interactions with waves and tides
and further accelerating beach erosion (Cooper and McKenna 2008). The
combined effects of rising sea levels and coastal armouring are therefore
expected to have an unprecedented ecological impact on beaches (Defeo
et al. 2009).
Effects of Ocean Acidifi cation
Today, surface waters are saturated with respect to calcium carbonate, but
increasing levels of atmospheric carbon dioxide are reducing ocean pH
and carbonate ion concentrations, and thus the level of calcium carbonate
saturation (Orr et al. 2005). There is every indication that these changes
will have a signifi cant impact on species that produce hard structures
such as skeletons, shells, and on tests of biogenic calcium carbonate (e.g.,
molluscs, crustaceans, echinoderms, protists, algae). Recent work suggests
that benthic adult molluscs and echinoderms are sensitive to changes in
seawater carbonate chemistry (Shirayama and Thornton 2005). There was
a signifi cant reduction in the growth rate, size and body weights and shell
dissolution in specimens of the mussel Mytilus galloprovincialis and sea
urchins Hemicentrotus pulcherrimus and Echinometra mathaei when they
were exposed to low pH (Shirayama and Thornton 2005). Calcifi cation
rates in Mytilus edulis were observed to decline linearly with increasing
CO 2 levels, and 70% of oyster Crassostrea gigas larvae reared under pH 7.4
were either completely non-shelled, or only partially shelled, in contrast
to 70% successful development in control embryos (Kurihara 2008).
In addition, higher levels of CO 2 partial pressures (hypercapnia) will
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