Projected changes to mangroves, seagrass and tidal flats

Projected changes to mangroves, seagrass and tidal flats

Presented by Johanna Johnson

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

Authors

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

• Direct removal and/or damage of mangroves and seagrass

• Sand mining impacts on intertidal flats

• Natural disturbances

+SST+SST

Projected climate change

1980–1999average

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 9Number of tropical cyclones may decrease but likely to be more intense

a = since 1960

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 change

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 low–moderate vulnerability to climate change

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

Seagrasses2035 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

Projected habitat change in FijiLoss 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 -10 to -20

Likelihood

Confidence

0% 66% 90% 100%29%

100%

Somewhat likelyUnlikely Likely Very likely

5% 33% 66% 95%0%

LowVery low HighMedium Very high

Likelihood

Confidence

0% 66% 90% 100%29%

100%

Somewhat likelyUnlikely Likely Very likely

5% 33% 66% 95%0%

LowVery low HighMedium Very high

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

[email protected]