Transcript 09. Coastal habitats Johnson

Projected changes to mangroves,
seagrass and tidal flats
Presented by
Johanna Johnson
Authors
This presentation is based on Chapter 6 ‘Vulnerability of
mangroves, seagrasses and intertidal flats in the tropical
Pacific to climate change’ in the book Vulnerability of
Tropical Pacific Fisheries and Aquaculture to Climate
Change, edited by JD Bell, JE Johnson and AJ Hobday and
published by SPC in 2011.
The authors of Chapter 6 are: Michelle Waycott, Len J
McKenzie, Jane E Mellors, Joanna C Ellison, Marcus T
Sheaves, Catherine Collier, Anne-Maree Schwarz, Arthur
Webb, Johanna E Johnson and Claude E Payri
Coastal habitats: role
• Mangroves, seagrasses and intertidal flats
provide nursery and feeding areas for
coastal fish and shellfish
• Targeted invertebrates reside permanently
in seagrasses (e.g. sea cucumbers and
molluscs)
• Maintaining these habitats is critical for
coastal fisheries (e.g. 3,550 tonnes of
inter/subtidal invertebrates are harvested
per year in Fiji)
Coastal habitats: role
mangroves
seagrasses
Coastal habitats: Fiji
• Large areas of mangroves (425 km2 ) and
seagrass (16.5 km2 )
• Documented relationship between rainfall
patterns and mangrove reproductive
success
• One of few places deep sea seagrasses have
been reported, at Great Sea Reef
• Provide over 17,000 tonnes of fish each
year
Existing threats
• Poor catchment management – transport of
terrestrial sediments, nutrients and pesticides
+SST
• Direct removal and/or damage of mangroves
and seagrass
• Sand mining impacts on intertidal flats
• Natural disturbances
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
Vulnerability: 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
Vulnerability: seagrasses
• Most vulnerable to:
– increasing air and sea temperatures
– changed rainfall patterns (increasing terrestrial
sediment and nutrient inputs)
– more intense cyclones and storms
• Seagrasses in estuaries, fringing reefs and
lagoon habitats will be most impacted
• Limited ability to adapt
• Overall moderate vulnerability to climate
Vulnerability: intertidal flats
• Most vulnerable to sea-level rise
• Ability to adapt by migrating landward as sealevel rises but human barriers and narrow
atolls may constrain this
• Overall low–moderate vulnerability to climate
change
Overall vulnerability
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
Seagrasses
2035 A2
Moderate
Moderate
Very low
Moderate Moderate
Low
Low
2050 A2
Moderate
Moderate
Very low
Moderate Moderate Moderate
2100 A2
High
High
Very low
High
High
Moderate
Low
Moderate
Projected habitat change in Fiji
Loss of habitat area: from 425 km2 (m) & 16.5 km2 (s)
Year
Scenario
Mangrove area (%)
Seagrass area (%)
2035
A2
-10
< -5
2050
A2
-50
-5 to -10
2100
A2
-60
Unlikely
Somewhat
likely
-10
to -20
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%
Vulnerable PICTs
CNMI, FSM, Fiji, French Polynesia, Guam, Kiribati, New
Caledonia, Palau, PNG, Samoa, Solomon Islands, Tonga,
Vanuatu
Key adaptations
1. Build resilience of coastal habitats 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:
– Provide for landward migration of coastal fish
habitats
Conclusions
• Mangroves, seagrasses and intertidal flats (with coral
reefs) support important coastal fisheries in Fiji
• Coastal habitats in Fiji 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
• Information on the distribution, diversity and area of
these habitats, and future changes is a critical gap
• Coastal fisheries that depend on these habitats will be
impacted as these habitats degrade
Thank you
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