Geoscience Reference
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4.3.4 Coral reef ecosystems
A conservative estimate of the total area covered by coral reefs is 62,000 km 2 and the eco-
nomic value of all ecosystem services provided by corals approaches US$ 365 billion per
year globally (Costanza et al., 1997 ) . Climate change is threatening tropical marine habit-
ats across the world, with coral bleaching, invasive species, and community shifts linked
to rising sea temperatures and acidification (Pandolfi et al., 2005 ; Poloczanska et al., 2007 ;
Lough, 2008 ) . Current research on the impacts of climate change on tropical fauna is mainly
focused on corals (Hoegh-Guldberg, 2004 ; Willis et al., 2006 ; Smith et al., 2007 ; Lough,
2008 ) and associated fishes (Roessig et al., 2004 ; Graham et al., 2006 ; Wilson et al., 2006 ;
Munday et al., 2007 ) . Substantial impacts on community structure have been observed in
coral reefs during periods of warmer than normal sea temperatures (Walther et al., 2002 ;
Przeslawski et al., 2008 ). Poised near their upper thermal limits, coral reefs have undergone
global mass bleaching events whenever sea temperatures have exceeded long-term summer
averages by more than 1.0°C for several weeks (Wilkinson, 2000 ; Walther et al., 2002 ) . The
most severe period occurred in 1998, during which an estimated 16% of the world's reef-
building corals died (Wilkinson, 2000 ) . The impact of thermal stress on reefs can be dramat-
ic, with almost total removal of corals in some instances (Hoegh-Guldberg, 1999 ) . In some
cases branching acroporid and pocilloporid corals have bleached and/or died, leaving more
massive species like Porites spp. intact. In other cases, all coral species have largely been
removed (Mumby et al., 2001 ;Loya et al., 2001 ).Estimates ofhowecosystem species' rich-
ness and community structure have changed after bleaching events are generally not avail-
able, but such changes are suspected to be large. When coral loss has been severe, reef fish
biodiversity declines (Jones et al., 2004 ; Graham et al., 2006 ; Wilson et al., 2006 ) and the
loss of key species within critical functional groups, or the complete loss of entire functional
groups, can have a profound effect on reef resilience (Bellwood et al., 2004 ) .
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