Projected changes to mangroves, seagrass and tidal flats

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Projected changes to mangroves, seagrass and
tidal flats
Presented by Johanna Johnson
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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

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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)

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Coastal habitats role
mangroves
seagrasses
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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

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Existing threats

• Poor catchment management transport of
  terrestrial sediments, nutrients and pesticides
• Direct removal and/or damage of mangroves and
  seagrass
• Sand mining impacts on intertidal flats
• Natural disturbances

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Projected climate change
  19801999 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 -5 to -20 10 to 20 -5 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 Number of tropical cyclones may decrease but likely to be more intense Number of tropical cyclones may decrease but likely to be more intense
a since 1960
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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

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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 change

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Vulnerability intertidal flats

• Most vulnerable to sea-level rise
• Ability to adapt by migrating landward as
  sea-level rises but human barriers and narrow
  atolls may constrain this
• Overall lowmoderate vulnerability to climate
  change

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Overall vulnerability
  Sea surface temperature Solar radiation Ocean chemistry Cyclones storms Rainfall patterns Sea level Nutrients
Mangroves 2035 A2 Very low Low Very low Moderate Low High Low
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 Low
2100 A2 High High Very low High High Moderate Moderate
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Projected habitat change in Fiji

• Loss of habitat area from 425 km2 (m) 16.5 km2
  (s)

Year Scenario Mangrove area () Mangrove area () Seagrass area () Seagrass area ()
2035 A2 -10 lt -5
2050 A2 -50 -5 to -10
2100 A2 -60 -10 to -20
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Vulnerable PICTs
CNMI, FSM, Fiji, French Polynesia, Guam,
Kiribati, New Caledonia, Palau, PNG, Samoa,
Solomon Islands, Tonga, Vanuatu
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Key adaptations

• Build resilience of coastal habitats 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
• Provide for landward migration of coastal fish
  habitats

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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

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Thank you
j.johnson_at_c2o.net.au