Projected changes to coral reefs

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Projected changes to coral reefs
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Based on......
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Outline

• Importance of coral reefs
• Different types of reefs
• Requirements for good coral growth
• Recent stresses on coral reefs
• Projected effects of climate change
• Key management measures

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Importance of coral reefs

• Form complex structures
• Provide habitat for thousands of species
• Support local fisheries and tourism
• Variation in local pressures

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Different types of reefs

• Dominant coastal habitat
• Majority are oceanic
• Great diversity of reef types
• Reef area in Cook Islands is gt2.7 times land area

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Location matters

• Fringing continental reefs affected by river
  runoff
• Isolated oceanic reefs not well connected e.g.
  larval supplies
• Tropical cyclones gt 10o from equator

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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
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Corals must build skeletons fast enough to
withstand natural forces of erosion
Cyclones storms
Waves
Predators
Bleaching
Coral eaters
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A special relationship

• Symbiosis is at the heart of tropical coral reefs
• Photosynthetic algae live within corals
• Algae give corals energy for rapid calcification

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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

Stressed - bleached
Healthy - unbleached
Recently dead
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Stresses ocean acidification

• 30 extra CO2 entered ocean
• Changes ocean chemistry
• Harder for corals to form skeletons
• Greater coral erosion

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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

Source Fabricius et al 2011
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Projected effects of climate change
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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
Cyclones storms 9 Number of cyclones/storms may decrease but likely to be more intense Number of cyclones/storms may decrease but likely to be more intense Number of cyclones/storms may decrease but likely to be more intense
a since 1960
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Warmer water temperatures

• Increased bleaching, 1 loss per year by 2035

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More acidic ocean

• Weaker reef frameworks

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Stronger storms and heavier rainfall

• Moderate vulnerability of reefs
• More disturbances less time to recover

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Higher sea level

• Some corals may keep up
• Loss of deeper corals

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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 are
likely to be MUCH SIMPLER ECOSYSTEMS
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Management of reefs
ALGAL REEFS
Mitigating local stresses
Anthony Maynard 2011
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Conclusions

• Coral reefs in Cook Islands are expected to
  decline in complexity and area due to climate
  change
• Coastal fisheries that depend on coral reef will
  be affected as coral reefs degrade
• Acting now to manage existing threats to coral
  reefs will assist these habitats to adapt and
  reduce the scale of degradation