Projected changes to coral reefs mangroves and seagrasses

Projected changes to coral reefs, mangroves and seagrasses

Based on. . .

Outline • • Coastal habitats: roles and values Requirements for good coral growth 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 -2 o. C below upper thermal limit • Too much freshwater can also cause bleaching Healthy - unbleached Stressed - bleached Recently dead

Stresses – ocean acidification • 30% extra CO 2 entered ocean • Changes ocean chemistry • Harder to form skeletons • Greater coral erosion

Ocean acidification: natural laboratory • High CO 2 volcanic seeps, PNG • “Winners” = massive corals • “Losers” = branching, tabulate corals • Reduced coral diversity • Much simpler reef with lower p. H Normal p. H = now Mid p. H = 2050 Lower p. H = 2100 Fabricius et al 2011

Source: http: //coralreefwatch. noaa. gov/satellite/vs/index. html

Projected Effects of Climate Change on Coral Ecosystems

Projected Regional Climate Change 1980– 1999 average 2035 A 2 2050 A 2 2100 A 2 Air temperature (°C) 27. 4 +0. 5 to +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 -5 to -20 Rainfall: equatorial (%) Rainfall: subtropics (%) n/a Sea level (cm) +6 a +20 to +30 Ocean p. H (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

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

CORAL DOMINATED TO ALGAL DOMINATED REEFS

Projected loss of coral reefs A 2 2050 A 2 2100 >90% Loss Of Coral Cover by 2100

Mangroves: role & value

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 A 2 Very low Low Very low Moderate 2050 A 2 Very low Low Very low Moderate Very high Low 2100 A 2 Very low Low Very low Moderate Very high Low

Projected loss of mangroves in VANUATU From 25 km 2 today: Year Mangrove area (%) 2035 -10 2050 -50 2100 -60

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 Seagrasses 2035 A 2 2050 A 2 2100 A 2 Sea surface Solar temperature radiation Moderate High Ocean chemistry Cyclones & storms Very low Rainfall patterns Sea level Nutrients Moderate Low Low Moderate High

Projected loss of seagrass in Vanuatu From ? ? km 2 today: Year Seagrass area (%) 2035 -5 to -20 2050 -5 to -30 2100 -10 to -35

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 Vanuatu 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