Seaweeds Ecology and Climate Change - Marine Ecology in a Changing World - page 182

Interaction between seaweeds and corals in the context of ocean
acidifi cation
General predictions suggest that the ocean acidifi cation can lead to reduced
calcifi cation rates of corals (Kleypas and Langdon 2006, Anthony et al.
2008). Reducing the potential for coral growth would lead to changes in the
competitive process between corals and seaweeds and promote changes
leading to the dominance of seaweeds (Carilli et al. 2009).
A recent study has attempted to predict that the increase of CO 2 modifi es
the interactions between seaweeds and corals. The results showed that the
CO 2 level is signifi cantly correlated with the decline in coral growth rates
and also with coral mortality which was also increased by contact of the
coral with the seaweeds (Diaz-Pulido et al. 2011). In general, an increase in
growth rate of seaweed coupled with a decrease in coral growth rate and
increased coral mortality with increasing atmospheric CO 2 would give rise
to changes in the competitive interaction between corals and seaweeds
and therefore the dynamics of reef communities would be altered (Diaz-
Pulido et al. 2011). Similar results have been found by other authors who
have predicted that ocean acidifi cation will have a signifi cant reduction
in the resilience of coral specifi cally because it will reduce the growth rate
due to accretion, which in addition to interaction processes between corals
and seaweed, would lead the community to states of seaweed dominance
(Hoegh-Guldberg et al. 2007, Anthony et al. 2011).
The effects of ocean acidifi cation on seaweed epibionts
Seaweeds are key species of some benthic coastal ecosystems in which they
constitute the main substrate for many epibionts such as bryozoans and
tubeworms. Epibionts of seaweeds may also be affected by acidifi cation
of the oceans, either directly due to changes in abundance of seaweed or
indirectly through changes in the physiology of the host. A recent study
has shown that biological activity of the host could modulate the pH and
therefore the conditions of CO 2 in the boundary layer of the thallus where
the epibionts live due to a dominance of the photosynthetic activity over
acidifi cation (Saderne and Wahl 2012).
General Conclusions
Several aspects of the biology and ecology of seaweeds are infl uenced
by global environmental changes such as increase in superfi cial seawater
temperature, solar UV-B irradiance, atmospheric CO 2 concentration, and
sea level (Fig. 3). Elevated temperature negatively affects most aspects
of the biology of kelps and fucoids (e.g., reproduction, recruitment and
growth, and resilience to disturbances). Hence, projected global warming