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Vulnerability of coral reefs

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  1. Vulnerability of coral reefs Janice Lough

  2. Moving reefs out of comfort zone Hoegh-Guldberg et al 2007

  3. 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

  4. 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

  5. With different levels of human use • support local fisheries • differences in local pressures

  6. 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

  7. Important environmental factors • warm water temperatures • shallow well-lit waters • low sediment and nutrients • right ocean chemistry Ω >3.3 • warmest parts of oceans • narrow temperature range

  8. Corals must build skeletons fast enough to withstand natural forces of erosion tropical cyclones waves sunshine predators coral eaters

  9. 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

  10. Relationship breaks down due to stress • 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 Healthy - unbleached Recently dead Stressed - bleached

  11. Ocean acidification • 30% extra CO2 entered oceans • otherwise greater warming! • BUT changes ocean chemistry • harder to form skeletons & shells • more erosion

  12. Ocean acidification: natural laboratory Lower pH = 2100 • high CO2 volcanic seeps, PNG • “winners” = massive corals • “losers” = branching, tabulate corals • reduced coral diversity • much simpler reef with lower pH Mid pH = 2050 Normal pH = now Fabricius et al 2011

  13. Warmer temperatures • very high vulnerability • already seen bleaching, diseases

  14. More acidic ocean • high vulnerability • weaken reef framework

  15. Stronger storms and heavier rainfall • moderate vulnerability • more disturbances = less time to recover

  16. Higher sea level • some corals may keep up • loss of deeper corals

  17. Opportunities for management interventions Anthony & Maynard 2011

  18. Reef status: Fiji • value of monitoring – appears “stable” condition • tropical cyclones, bleaching, COTs • recovery after disturbance • localised pollution/overuse • 34% of reefs classed at “low threat” Morris & Mackay (2008) Status of coral reefs of the world 2008

  19. 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

  20. 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 BUT likely to be MUCH SIMPLER ECOSYSTEMS

  21. Thank you j.lough@aims.gov.au