coral bleaching . why bleaching?
TRANSCRIPT
Coral Bleaching
www.ogp.noaa.gov
Why Bleaching?
Sun exposed areas bleach first
Photosynthesis (normal conditions)
Photosynthesis under thermal stress(Photoinhibition bleaching model)
Thermal thresholds(Temperatures at which bleaching occurs)
Hoegh-Guldberg 1999
El Niño
La Niña
Tahiti Sea Surface temperature
Hoegh-Guldberg 1999
Number of reefs severely bleaching
Hoegh-Guldberg 1999
1998 Massive Bleaching
Question 1:
• Why are corals growing so close to their thermal limit?
Predicted evolution SST(Global coupled atmosphere-ocean-ice model)
Hoegh-Guldberg 1999
Question 2:
• Why are corals growing so close to their thermal limit?
• Why are there few reports of coral bleaching before 1979?
Predicted evolution SST(Global coupled atmosphere-ocean-ice model)
Hoegh-Guldberg 1999
Question 3:
• Why are corals growing so close to their thermal limit?
• Why are there few reports of coral bleaching before 1979?
• Will coral bleaching increase in the future?
Hoegh-Guldberg 1999
Possible scenarios of increasing SST
• Strategy shift: – Hardy spp. replace sensitive spp.
• Tolerance: Corals acclimate + evolve– spp. with highest genetic variability expected to
survive
• Phase shift: corals are replaced by algae– Already occurring in many regions!
Simple Model
Model with interspecific differences in thermal thresholds
Model with thermal threshold differences + acclimation & evolution
Hughes et al. 2003
Interspecific bleaching Susceptibility
Diverse Communities
Monospecific communities
Interspecific Bleaching Susceptibility Raiatea, French Polynesia (May 2002)
Hughes et al. 2003
Coral species boundaries(geographical differences)
1- Local Temperature differences2- Genetic Variability differences
Low-Isolated endemic populationsHigh-Central and Mainland populations
Hughes et al. 2003
Facts on the future of Coral Reefs due to Global warming
• Few indications that coral acclimation / rapid evolution is occurring
• Oceans warming 2oC / 100 years• Annual massive bleaching events by
2030-2070• Phase shift away from coral dominated
communities by 2050• Economical impact of Trillions of $,
affecting 100’s of million humans
Coral-Algae Phase Shift (Jamaica)
Algae Coral (% cover)
1984 3% 53%
1995 92% 4%
Herbivory in Coral Reefs
Coral reef herbivores?
• Green Turtles– Ecologically extinct
• Manatees & Dugongs– Ecologically extinct
• Parrotfish (& surgeonfish)– Generally overfished
• Sea Urchins– Variable abundance (diseases & predation)
Jamaican History 101• 1492: 16 million Green Turtles (Caribbean)
• 1688-1730: 13000 turtles/year (slave food)
• 1730: 6.5 million Turtles (Caribbean)
• 1800: Turtle fishery crashes, Fish fishery develops
• 1881: Jamaica imports 85% of its fish (local overfishing)
• 1962: Historical high fishery catches (15% local origin)(local overfishing still)
No Turtles, No manatees, Very few parrotfishONLY SEA URCHINS LEFT
(Diadema antillarum)
Jamaican History 102• 1980: Hurricane Allen
• 1983: Diadema die-off across Caribbean (99% mortal.)
NO HERBIVORES LEFT!
• Late 1980’s: Shift to Algal Domination
• 1991: Hurricane Gilbert
• Today:– Algae dominate reefs– Extensive overfishing of herbivore fish species– Slow and patchy recovery of Sea Urchins populations
Historical coral reef community changes
% r
eef
site
s
P = PrehumanH = Hunter GathererA = AgriculturalCO+CD = ColonialM1 = ModernM2 = Present
Historical coral reef degradation
Increase Coral DiseasesMassive Bleaching
OVERFISHING
Principle 15 of the Rio Declaration
• “Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.”
