Environmental Engineering Reference
In-Depth Information
Effects of seawater acidifi cation on seaweed population and community
ecology
Unlike the projections about the potential effects of ocean acidifi cation at
physiological level of seaweeds, which can be estimated using controlled
culture experiments of individuals, the predictions for populations and
communities from an ecological point of view are more complex. Attempts
to determine whether the predictions based on laboratory experiments
translate to the conditions of the natural environment have been hampered
by the diffi culty to simulate the conditions of ocean acidifi cation and to
test the hypotheses in experiments that require the manipulation of CO
2
concentration for long periods of time. However, some studies have drawn
these diffi culties by taking advantage of high CO
2
conditions present in
natural environments that may simulate future conditions such as pH
gradient that occur as a result of volcanic discharges or leaks (Hall-Spencer
et al. 2008, Porzio et al. 2011). In example, a study about the impact of
decreased pH on seaweeds communities have predicted changes in species
richness, decrease of turf forming species, inhibition of reproduction,
decrease in coverage and number of calcifi ed seaweeds and dominance of a
few species of non-calcifi ed seaweeds. These results were exacerbated when
the pH reached very low levels (Porzio et al. 2011). Another recent study at
ecosystem-level showed that communities of rocky shores where calcareous
organisms were abundant shifted to communities with scarcity of corals
and signifi cant reductions in coverage and abundance of Corallinaceae
under conditions of low pH. On the other hand, some seaweed genera were
resilient to high levels of CO
2
, such as
Caulerpa, Cladophora, Asparagopsis,
Dictyota
and
Sargassum
, some of which are considered alien species (Hall-
Spencer et al. 2008).
Ocean acidifi cation and calcifi ed seaweeds
Many studies concerning the effect of ocean acidification on marine
organisms have shown that calcifi ed organisms would be more susceptible
due to the reduced availability of the chemical constituents that they
use to synthesize calcifi ed structures (Kroeker et al. 2010). Seaweeds
that have calcium carbonate structures include crustose seaweed and
seaweed belonging to the group Corallinaceae. The calcifi ed seaweeds
use aragonite or calcite as a form of calcium carbonate to synthesize their
thalli (Lowenstam 1981). The direct effect of seawater acidifi cation on
these compounds is the reduction of their concentration and therefore
its availability in the form of carbonate ions (Díaz-Pulido et al. 2007).
These conditions may predict a reduction in the rate of calcifi cation of the
structures of calcifi ed seaweeds facing CO
2
enrichment conditions due to
