Projected changes to coral reefs,
mangroves and seagrasses
Solomon Islands Government
Based on......
Outline
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Coastal habitats: roles and values
Requirements for good coral growth
Recent stresses on coral reefs
Projected effects of climate change on:
– coral reefs
– mangroves
– seagrasses
• Key management measures
Requirements for good coral growth
• Warm water temperatures
• Shallow well-lit waters
• Low sediment and nutrients
• Right ocean chemistry
Coral reefs grow in the warmest parts of
oceans & have a narrow temperature range
Corals must build skeletons fast enough to
withstand natural forces of erosion
waves
cyclones & storms
bleaching
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 freshwater can also cause bleaching
Healthy - unbleached
Stressed - bleached
Recently dead
Stresses – ocean acidification
• 30% extra CO2 entered ocean
• 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
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
Cyclones & storms
9
a = since 1960
+70 to +110
-0.2
+90 to +140
-0.3
Number of cyclones/storms may decrease but
likely to be more intense
Warmer water temperatures
• Reefs 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 of reefs
• More disturbances = less time to recover
Higher sea level
• Some corals may keep up
• Loss of deeper corals
Opportunities for interventions
Anthony & Maynard 2011
What climate change means for reefs
• More bleaching and diseases
• Weaker skeletons
• Physical destruction
• Less time to recover between disturbances
• Healthy reefs better able to cope
Coral reefs will not disappear entirely BUT
likely to be
MUCH SIMPLER ECOSYSTEMS
Mangroves: role
Vulnerability of mangroves
• Most vulnerable to:
– sea-level rise
– increasing storm intensity
• Ability to adapt by migrating landward as sea-level
rises but human barriers may constrain movement
• Overall moderate-high 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
Solomon Islands
From 525 km2 today:
Year
Mangrove area (%)
2035
-10
2050
-50
2100
-60
Unlikely
Somewhat likely
Likely
Very low
Very likely
Very likely
29%
Low
66%
Medium
90% 100%
High
Very high
Confidence
Likelihood
0%
Very low
Confidence
Likely
Likelihood
0%
Unlikely
Somewhat likely
29%
Low
66%
Medium
90% 100%
High
Very high
0% 5%
33%
66%
95% 100%
Vulnerability of seagrasses
• Most vulnerable to:
– Warmer waters
– Increased rainfall (turbidity)
– Increasing storm intensity
– Reduced light
• Limited ability to adapt
• Overall moderate vulnerability to climate change
Overall vulnerability of seagrasses
Sea surface
Solar
temperature radiation
Seagrasses
2035 A2
2050 A2
2100 A2
Moderate
Moderate
Moderate
Moderate
High
High
Ocean
chemistry
Cyclones
& storms
Very low
Very low
Very low
Rainfall
patterns
Sea level
Nutrients
Moderate Moderate
Low
Low
Moderate Moderate
Low
Low
Moderate
Moderate
High
High
Projected loss of seagrass in Solomon
Islands
From 66 km2 today:
Year
Seagrass area (%)
2035
-5 to -20
2050
-5 to -30
2100
-10 to -35
Unlikely
Somewhat likely
Likely
Very low
Very likely
Very likely
29%
Low
66%
Medium
90% 100%
High
Very high
Confidence
Likelihood
0%
Very low
Confidence
Likely
Likelihood
0%
Unlikely
Somewhat likely
29%
Low
66%
Medium
90% 100%
High
Very high
0% 5%
33%
66%
95% 100%
Key management measures
1. Build health of coral reefs, mangroves and
seagrass 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, mangroves and seagrasses in Solomon
Islands 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
Thank you
j.johnson@c2o.net.au