Environmental Engineering Reference
In-Depth Information
substrate for propagules settlement allowing colonization and development
of new subtidal populations, increasing the range of spatial distribution of
seaweeds. However, subtidal seaweed communities would also be affected
due to increased depth and the consequent reduction of the incidence of
light on the water column would limit photosynthesis. These changes would
lead to the displacement of their communities from the subtidal towards the
intertidal resulting in changes of zonation patterns (Harley et al. 2006).
Another less direct consequence, but with great long-term effect of
sea-level rise comes from the change in the relationship between vertical
and horizontal surfaces of the substrate, especially in areas where the tide
amplitude is small (Vaselli et al. 2008). In regions where most of the rocky
coast is horizontal, a rapid increase in sea-level could cause fl ooding of most
of the intertidal zone, transforming the platforms into subtidal reefs.
Rising sea level can also affect the diversity of seaweed communities in
coastal areas through changes in the characteristics of the substrate. Field
measurements on the rocky coast of the Mediterranean Sea showed that an
increase in sea level in the range of 5 to 50 cm may increase the availability of
steeped substrate up to 58% compared to current conditions and suggested
that a change in the tilt of the substrate affects the ability of assemblages
to recover after a disturbance; leading to an expansion of assemblages
dominated by crustose algae and reduced abundance of fi lamentous forms
(Vaselli et al. 2008).
A valuable and highly diverse coastal ecosystem that is affected and
threatened by the rise in sea-level is the coral reef, which exhibits high
diversity of seaweed species (Wilkinson 2004, Hoegh-Guldberg et al. 2007).
One of the direct effects of rising sea level on seaweed that live on coral reef
is the habitat loss due to subsidence of these reefs as sea level rises over
them (Diaz-Pulido et al. 2007). Another equally important consequence is
that the rise in sea level could induce an acceleration of vertical growth rates
of coral to a maximum level, although this would not be enough to keep
off the rate of increase in sea level and therefore less protected reefs will
decrease their growth rate as a result of fl ooding and erosive effect that the
waves could produce grades in them (Buddemeier and Smith 1988).
Ocean acidifi cation
Carbon dioxide (CO
2
) levels in the atmosphere have strongly increased
during the last millennium as a result of human activities related to the
use of fossil fuel, deforestation and agriculture (IPCC 2001). This sudden
increase in atmospheric CO
2
concentration levels brings several global side
effects, and one of the most important is the ocean acidifi cation.
