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Projected changes to coral reefs and mangroves. Based on. What we will discuss. Projected changes to atmospheric and oceanic conditions. Ecosystems supporting fish. Fish stocks/aquaculture species. Implications for economic development, food security and livelihoods.
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What we will discuss Projected changes to atmospheric and oceanic conditions Ecosystems supporting fish Fish stocks/aquaculture species Implications for economic development, food security and livelihoods Adaptations and policies to reduce threats and capitalise on opportunities
Outline • Requirements for good coral growth • Recent stresses on coral reefs • Projected effects on coral reefs • Mangroves
Requirements for good coral growth • Warm water temperatures • Shallow well-lit waters • Low sediment and nutrients • Right ocean chemistry Ω >3.3 • Warmest parts of oceans • Narrow temperature range
Corals must build skeletons fast enough to withstand natural forces of erosion tropical cyclones waves sunshine predators coral eaters
A special relationship • Symbiosis at heart of tropical coral reefs • Photosynthetic algae live within coral animal • Corals get enough energy for rapid calcification • Form structurally complex reefs • Home to thousands of other plants and animals
Stresses – higher water temperatures • Stressed corals lose algae (and their pigments) • Coral bleaching • Corals living only ~1-2oC below upper thermal limit • Too much fresh water also causes bleaching Healthy - unbleached Recently dead Stressed - bleached
Stresses - ocean acidification • 30% extra CO2 entered ocean • Prevents greater warming! • BUT changes ocean chemistry • Harder to form skeletons • Greater coral erosion
Ocean acidification: natural laboratory Lower pH = 2100 • High CO2 volcanic seeps, PNG • “Winners” = massive corals • “Losers” = branching, tabulate corals • Reduced coral diversity • Much simpler reef with lower pH Mid pH = 2050 Normal pH = now Fabricius et al 2011
Projected climate change a = since 1960
Warmer water temperatures • Very high vulnerability • Increased bleaching, ~1% loss per year by 2035
More acidic ocean • Reefs have high vulnerability • Weaker reef frameworks
Stronger storms and heavier rainfall • Moderate vulnerability • More disturbances = less time to recover
Higher sea level • Some corals may keep up • Loss of deeper corals
Opportunities for management interventions Anthony & Maynard 2011
What CC means for coral reefs • Bleaching and diseases • Weaker skeletons • Physical destruction • Less time to recover between disturbances • Healthy reefs better able to cope • Can adaptation occur? Coral reefs will not disappear entirely BUT likely to be MUCH SIMPLER ECOSYSTEMS
Vulnerability of mangroves • Most vulnerable to: • sea-level rise • decreasing rainfall • increasing cyclone intensity • Ability to adapt by migrating landward as sea-level rises but human barriers may constrain movement • Overall moderate vulnerability to climate change
Projected loss of mangroves in Samoa From 7.5 km2 today
Key adaptations • Build resilience of coral reefs and mangroves by addressing existing threats: • Integrated catchment management • Foster the care of coastal fish habitats • Manage and restore coastal vegetation • New measures to allow future adaptation of mangroves: • Provide for landward migration
Conclusions • Coral reefs and mangroves in Samoa are expected to decline in area due to climate change • Acting now to manage existing threats and allow for future adaptation is vital for these habitats • Coastal fisheries that depend on these habitats will be affected as these habitats degrade