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
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•
•
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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
0%
Medium risk
6%
High risk
43%
Very High risk
51%
Medium risk
or higher
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
+5 to +20
+10 to +20
+10 to +20
-5 to -20
-5 to -20
-5 to -20
Rainfall: equatorial (%)
Rainfall: subtropics (%)
n/a
Sea level (cm)
+6a
+20 to +30
Ocean pH (units)
8.1
-0.1
Tropical cyclones
9
a = since 1960
+70 to +110
-0.2
+90 to +140
-0.3
Number of tropical cyclones may decrease but
likely to be more intense
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
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
Solar
temperature radiation
Ocean
chemistry
Cyclones
& storms
Rainfall
patterns
Sea level
Nutrients
Low
High
Low
Mangroves
2035 A2
Very low
Low
Very low
Moderate
2050 A2
Very low
Low
Very low
Moderate Moderate
Very high
Low
2100 A2
Very low
Low
Very low
Moderate Moderate
Very high
Low
Projected loss of mangroves in Samoa
From 7.5 km2 today
Year
Mangrove area (%)
2035
-10
2050
-50
2100
-60
Unlikely
Somewhat likely
Likely
Very likely
Likelihood
0%
Unlikely
Somewhat likely
Likely
Low
66%
Medium
90% 100%
High
Very high
Confidence
Likelihood
0%
Very low
Confidence
Very low
Very likely
29%
29%
Low
66%
Medium
90% 100%
High
Very high
0% 5%
33%
66%
95% 100%
Key adaptations
1. 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
2. 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