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Vulnerability of coral reefs. Janice Lough. Moving reefs out of comfort zone. Hoegh-Guldberg et al 2007. Outline Coral Reefs. key coastal ecosystem many different reef types narrow environmental limits already shown impacts, e.g. bleaching combined effects of disturbances - PowerPoint PPT Presentation
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Vulnerability of coral reefs
Janice Lough
Moving reefs out of comfort zone
Hoegh-Guldberg et al 2007
Outline Coral Reefs• key coastal ecosystem• many different reef types• narrow environmental limits• already shown impacts, e.g. bleaching• combined effects of disturbances• less time to recover• simpler reefs• healthy reefs will cope better
Many different types of reefs
• 13/22 PICTS have more reef than land area (e.g. ~Fiji 40%)
• dominant coastal habitat
• majority are oceanic• great diversity of reef
types
With different levels of human use
• support local fisheries
• differences in local pressures
Location matters• fringing continental reefs
affected by river runoff
• isolated oceanic reefs not
well connected e.g. larval
supplies
• tropical cyclones> 10o
from equator
• El Niño/La Niña impacts
Important environmental factors
• warmest parts of oceans
• narrow temperature range
• warm water temperatures
• shallow well-lit waters
• low sediment and nutrients
• right ocean chemistry Ω >3.3
Corals must build skeletons fast enough to withstand natural forces of erosion
coral eaterspredators
waves
sunshine
tropical cyclones
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
• stressed corals lose algae (and their pigments)
• coral bleaching
• seen more frequently due to warmer temperatures
• corals living only ~1-2oC below upper thermal limit
• too much fresh water also causes bleaching
Relationship breaks down due to stress
Healthy - unbleached
Stressed - bleached Recently dead
• 30% extra CO2 entered oceans
• otherwise greater warming!
• BUT changes ocean chemistry
• harder to form skeletons &
shells
• more erosion
Ocean acidification
Ocean acidification: natural laboratory
Normal pH = now Mid pH = 2050 Lower pH = 2100
Fabricius et al 2011
• high CO2 volcanic seeps, PNG
• “winners” = massive corals
• “losers” = branching, tabulate corals
• reduced coral diversity
• much simpler reef with lower pH
Warmer temperatures• very high vulnerability• already seen bleaching, diseases
More acidic ocean• high vulnerability• weaken reef framework
Stronger storms and heavier rainfall• moderate vulnerability• more disturbances = less time to recover
Higher sea level• some corals may keep up• loss of deeper corals
Opportunities for management interventions
Anthony & Maynard 2011
Morris & Mackay (2008) Status of coral reefs of the world 2008
• value of monitoring – appears “stable” condition• tropical cyclones, bleaching, COTs• recovery after disturbance• localised pollution/overuse• 34% of reefs classed at “low threat”
Reef status: Fiji
What it means for coral reefs• already shown vulnerability
• bleaching and diseases
• physical destruction
• weaker skeletons
• lower salinity
• connectivity between reefs
• direct & indirect effects on other reef organisms
Summary key issues• rates of change• combined stressors• less time to recover between disturbances• can adaptation occur in decades rather than 1000’s years?• healthy reefs better able to cope• consequences for reef-dependent fisheries
Coral reefs will not disappear entirely BUTlikely to be
MUCH SIMPLER ECOSYSTEMS
Thank you
j.lough@aims.gov.au
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