Coral Bleaching www.ogp.noaa.gov
Dec 18, 2015
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.”