Benthic Community and Climate Change - Marine Ecology in a Changing World - page 126

cover globally (Wilkinson 2002, Gardner et al. 2003, Hughes et al. 2003), a
trend that can be expected to continue as ocean temperatures rise (Hoegh-
Guldberg 1999).
Climate change is therefore likely to reduce local and regional coral
reef biodiversity, the elimination of sensitive species causing alterations in
the community structure of the reef (Graham et al. 2007). Most researchers
predict that the abundance of the more susceptible coral such as the
branching Acropora that form much of the habitat complexity of Indo-Pacifi c
reefs will decline as compared to less sensitive species such as slower-
growing genera with massive or encrusting growth forms (Pratchett et
al. 2011). When herbivores are absent or avoid macroalgal species, mass
bleaching can be followed by increases in macroalgae, thus reducing the
space available for coral recruitment (Pratchett et al. 2011). Following mass
bleaching events there is typically a decline in the abundance of fi shes and
invertebrates that consume or inhabit corals at least during some part of
their life cycle, accompanied by an increase in roving herbivores (Bellwood
et al. 2004). The limited evidence available of systematic changes in the
abundance of mesopredators or apex predators or of declines in fi sheries'
yields associated with bleaching suggests that such effects are likely to
manifest themselves in the long term (Pratchett et al . 2011).
Projections of the saturation levels of aragonite, a metastable form of
calcium carbonate used by many marine organisms, indicate a possible
30% decrease in coral calcifi cation rates over the next century (Gattuso et al.
1998, Langdon and Atkinson 2005), resulting in the slower growth of corals
as they become less able to compete for space, or weaker coral skeletons,
thus increasing their vulnerability to erosion, storm damage and predation.
Furthermore, since most reef habitats are of carbonate construction, any
loss of coral diversity will have a major knock-on effect on all reef-dwelling
taxa (Veron 2011).
The lesser known deep-sea corals living in cold waters below the photic
zone, at depths of 50-1000 m, are widely distributed, very long-lived (several
100s of years old), forming reef frameworks that persist for millennia, and
are considered to undergo relatively little environmental variability (Turley
et al. 2007). These biodiversity hotspots play an important role as a refuge,
feeding ground and nursery for deep-sea organisms, including commercial
fi sh (Rogers 1999, Fossa et al . 2002, Turley et al. 2007); however, their slow
growth and limited ability to recover make them particularly vulnerable
to anthropogenic activities such as bottom trawling, seabed mining, cable
and pipe laying, and oil and gas exploration (Turley et al . 2007). The
growing problem of ocean acidifi cation is also threatening their existence
(Guinotte et al . 2006) since the depth is in effect moving upwards as CO 2
concentrations rise and ocean acidifi cation increases, meaning that many
deep-sea coral ecosystems will soon be immersed in under-saturated waters.