of many reef islands. For example, simple models developed for linear and siliciclastic shorelines cannot be
directly applied to reef islands.
Reduced carbonate production and ocean
acidification
There is heightened concern that thermal stress due to
global warming (see Climate Change: Impact on Coral
Reef Coasts) and changes in ocean pH associated with fossil
fuel use (see Ocean Acidification, Effects on Calcification)
is reducing both the amount of calcium carbonate produced
on reefs and the durability of the sediments, both of which
have the capacity to influence reef sediment budgets and
ultimately the availability of sediments to maintain and
build reef islands. The intensity and scale of coral bleaching
has increased markedly since the 1960s, with entire reef
systems affected by major events in 1998 and 2002 (see
Temperature Change: Bleaching). Bleaching events not
only affect corals, but also affect other photosymbiotic
organisms such as foraminiferans that are very important
contributors to many reef islands (Yamano et al., 2000).
Calcification rates for corals on the world’s best-managed
reef – the GBR – are projected to decline by 14% compared
to 1990 (D’eath et al., 2009) and it has been further
projected that coral cover will decline on reefs beyond
2050 (Hoegh-Guldberg et al., 2007).
Some reef islands accumulated most of their mass long
ago, and these islands – especially if large and partially lithified – may be less sensitive to reduced carbonate production and ocean acidification in the short term. They will,
however, be less able to dynamically adjust to projected
changes in sea level and inundation. Where reef islands
are younger, more mobile, and generally on less emergent
reef flats, the future looks even less positive as active carbonate production and reef-island accumulation are more
tightly coupled on lower reef flats, with efficient transfer
of products to the zone of accumulation. In these circumstances, diminished carbonate productivity and sediment
supply will probably have more immediate effects on island
sediment budgets, morphologies, and prospects.
Bibliography
Aston, J. P., 1995. The Relative Mobilities of Coral Cays on the
Great Barrier Reef Can be Modeled. Townsville: James Cook
University, 267 p.
Bayliss-Smith, T. P., 1988. The role of hurricanes in the development of reef islands, Ontong Java atoll, Solomon Islands. Geographical Journal, 154, 377–391.
Chappell, J., Chivas, A., Wallensky, E., Polach, H. A., and
Aharon, P., 1983. Holocene palaeoenvironmental changes
Increased
cyclone activity
Ocean
acidification
Rubble production,
reduced structural integrity?
Rising sea
surface temperature
Enhanced
rainfall
Reduced
rainfall
Lower water table,
reduced vegetation
instability?
Increased vegetation
and stability?
Higher berms?
Higher waves
at shore
Exposure of
beachrock?
Shoreline erosion?
Shoreline accretion?
Rising
sea level
Calcification and reef growth
rates change, carbonate
producers and patterns change
Reduced CO 3 ion
availability and reduced
calcification
Increased coral
bleaching, loss of
sensitive species
Reduced structural
complexity
Increased bare substratum,
increased bioerosion,
secondary sediment production
Increased sediment transport?
Reef growth
‘Turned on’?
Increased depth, accommodation
space, and wave penetration
Coral Cay Classification and Evolution, Figure 9 Schematic summary of potential climate and sea-level change impacts on reef
islands.
CORAL CAY CLASSIFICATION AND EVOLUTION
251
directly applied to reef islands.
Reduced carbonate production and ocean
acidification
There is heightened concern that thermal stress due to
global warming (see Climate Change: Impact on Coral
Reef Coasts) and changes in ocean pH associated with fossil
fuel use (see Ocean Acidification, Effects on Calcification)
is reducing both the amount of calcium carbonate produced
on reefs and the durability of the sediments, both of which
have the capacity to influence reef sediment budgets and
ultimately the availability of sediments to maintain and
build reef islands. The intensity and scale of coral bleaching
has increased markedly since the 1960s, with entire reef
systems affected by major events in 1998 and 2002 (see
Temperature Change: Bleaching). Bleaching events not
only affect corals, but also affect other photosymbiotic
organisms such as foraminiferans that are very important
contributors to many reef islands (Yamano et al., 2000).
Calcification rates for corals on the world’s best-managed
reef – the GBR – are projected to decline by 14% compared
to 1990 (D’eath et al., 2009) and it has been further
projected that coral cover will decline on reefs beyond
2050 (Hoegh-Guldberg et al., 2007).
Some reef islands accumulated most of their mass long
ago, and these islands – especially if large and partially lithified – may be less sensitive to reduced carbonate production and ocean acidification in the short term. They will,
however, be less able to dynamically adjust to projected
changes in sea level and inundation. Where reef islands
are younger, more mobile, and generally on less emergent
reef flats, the future looks even less positive as active carbonate production and reef-island accumulation are more
tightly coupled on lower reef flats, with efficient transfer
of products to the zone of accumulation. In these circumstances, diminished carbonate productivity and sediment
supply will probably have more immediate effects on island
sediment budgets, morphologies, and prospects.
Bibliography
Aston, J. P., 1995. The Relative Mobilities of Coral Cays on the
Great Barrier Reef Can be Modeled. Townsville: James Cook
University, 267 p.
Bayliss-Smith, T. P., 1988. The role of hurricanes in the development of reef islands, Ontong Java atoll, Solomon Islands. Geographical Journal, 154, 377–391.
Chappell, J., Chivas, A., Wallensky, E., Polach, H. A., and
Aharon, P., 1983. Holocene palaeoenvironmental changes
Increased
cyclone activity
Ocean
acidification
Rubble production,
reduced structural integrity?
Rising sea
surface temperature
Enhanced
rainfall
Reduced
rainfall
Lower water table,
reduced vegetation
instability?
Increased vegetation
and stability?
Higher berms?
Higher waves
at shore
Exposure of
beachrock?
Shoreline erosion?
Shoreline accretion?
Rising
sea level
Calcification and reef growth
rates change, carbonate
producers and patterns change
Reduced CO 3 ion
availability and reduced
calcification
Increased coral
bleaching, loss of
sensitive species
Reduced structural
complexity
Increased bare substratum,
increased bioerosion,
secondary sediment production
Increased sediment transport?
Reef growth
‘Turned on’?
Increased depth, accommodation
space, and wave penetration
Coral Cay Classification and Evolution, Figure 9 Schematic summary of potential climate and sea-level change impacts on reef
islands.
CORAL CAY CLASSIFICATION AND EVOLUTION
251