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 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 waves tropical cyclones 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 Stressed - bleached Recently dead

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 High CO2 volcanic seeps, PNG “Winners” = massive corals “Losers” = branching, tabulate corals Reduced coral diversity Much simpler reef with lower pH Normal pH = now Mid pH = 2050 Lower pH = 2100 Fabricius et al 2011

Local stressors: reef status: Samoa Low risk Medium risk High risk Very High risk Medium risk or higher 0% 6% 43% 51% 100%

Projected effects of climate change

Projected climate change   1980–1999 average 2035 A2 2050 A2 2100 A2 Air temperature (°C) 27.4 +0.5 to +1.0 +1.0 to +1.5 +2.5 to +3.0 Sea surface temperature (°C) 27.3 +0.7 to +0.8 +1.2 to +1.6 +2.2 to +2.7 Rainfall: equatorial (%) Rainfall: subtropics (%) n/a +5 to +20 -5 to -20 +10 to +20 Sea level (cm) +6a +20 to +30 +70 to +110 +90 to +140 Ocean pH (units) 8.1 -0.1 -0.2 -0.3 Tropical cyclones 9 Number of tropical cyclones may decrease but likely to be more intense 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

Coral reefs will not disappear entirely BUT MUCH SIMPLER ECOSYSTEMS 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

Mangroves: role

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

Overall vulnerability of mangroves   Sea surface temperature Solar radiation Ocean chemistry Cyclones & storms Rainfall patterns Sea level Nutrients Mangroves 2035 A2 Very low Low Moderate High 2050 A2 Very high 2100 A2

Projected loss of mangroves in Samoa From 7.5 km2 today Year Mangrove area (%) 2035 -10 2050 -50 2100 -60

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