Factors influencing the Region’s values
Ocean acidification threatens physiological processes for a wide range of organisms.
capacity to create habitat for reef biodiversity in general.9 9,101 Additionally, if coral skeletons are weakened they may have lowered capacity to resist and recover from physical damage caused by cyclones.102 Reef development is thought to cease at pH 7.8.103 Field observations at natural carbon dioxide seeps have found more acidic oceanic conditions do not necessarily affect coral cover but reduce species diversity and structural complexity.103 Decreasing pH is likely to reduce the capacity of coralline algae, a species vital to reef building, to cement reef debris into solid limestone.70,104 It is also likely to affect coral recruitment and establishment.70 Other biota such as phytoplankton, foraminifera and molluscs are also at risk.104,105,106 The sensory systems, behaviours, and larval development and survival of a number of reef fish species including coral trout have been shown to be sensitive to increased temperature and acidity.107 Some seagrass and non-calcifying macroalgae may benefit from future ocean acidification.103,108,109 Rises in sea level are significant for the Great Barrier Reef ecosystem as some habitats are shallow and strongly influenced by sea level. In particular, because much of the land adjacent to the Great Barrier Reef is low lying, small changes in sea level will mean increased erosion and land inundation, causing significant changes in tidal habitats such as mangroves, and saltwater intrusion into low-lying freshwater habitats.110,111 Brackish saltmarsh habitats are being displaced by mangroves.112 Turtle and seabird nesting beaches, including on islands, are particularly vulnerable to rising sea levels, which exacerbate beach erosion113 and inundate nests114. As well as its direct effects on the Region’s ecosystem, climate change will also have indirect effects on the Reef’s resilience through amplifying the effects of other influencing factors such as coastal development and land-based run-off. For example, flood events carry pulses of nutrients, sediments, pesticides and other pollutants from the catchment, which have significant effects on inshore Great Barrier Reef habitats and species.115 Extreme weather events such as those in 2010–11 result in large amounts of marine debris washing or blowing into the Region from the catchment.116,117 Additionally, engineering solutions to improve the resistance of coastal assets to rising sea levels and increased storm intensities may interfere with the connectivity of coastal and marine systems or cause damage or loss of coastal habitats.118,119,120
6.3.3 Vulnerability of heritage values to climate change