Critical thresholds and the vulnerability of Australian tropical coastal ecosystems to the impacts of climate change
Paleoenvironmental studies of tropical coastal ecosystems in northern Australia indicate past responses to sealevel changes, implying geomorphological resilience in the face of future sea-level rise. However, there are several critical thresholds beyond which abrupt change appears inevitable. Elevated temperatures have recently caused extensive coral bleaching and reefs appear threatened if the thermal tolerance of corals is exceeded. Many reef islands have accumulated on reef platforms under stable or falling sea level. Continued accretion seems likely under gradual sea-level rise, but may no longer be sustainable if the sea drowns the reef platform on which they have formed. Similarly, broad mangrove-fringed plains have prograded under stable sea level, predisposing them to inundation if sea level continues to rise rapidly. The resilience of coastal ecosystems is also threatened by the synergistic interaction with several other pressures.