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Sea surface temperatures and coral reef bleaching off La Parguera, Puerto Rico (northeastern Caribbean Sea)

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Sea surface temperatures and coral reef bleaching off La Parguera, Puerto Rico (northeastern Caribbean Sea). Robinson Gaviria April 5, 2000

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Sea surface temperatures and coral reef bleaching off La Parguera, Puerto Rico (northeastern Caribbean Sea)

Robinson Gaviria

April 5, 2000

Winter A, Appeldroon RS, Brukner A, Williams EH, Goenaga C. 1998. Sea surface temperatures and coral reef bleaching off La Paraguera, Puerto Rico (northeastern Caribbean Sea). Coral Reefs 17: 377-382.

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Coral Bleaching

  • Occurs when corals lose/expel zoox or the zoox loose their chloroplast (pigmentation).
  • Bleaching generally occurs as a result of high relative (not absolute) water temperatures.
  • Generalized stress response by corals to environmental factors.
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Key ecological concepts

  • Symbiotic benefits between zooxanthellae and coral host results from the following:
  • The relationship of photosynthesis (primary production) to respiration.

6CO2 + 6H2O + light energy --->C6H12O6 (sugar) + 6O2

C6H12O6 (sugar) + 6O2 ----->6CO2 + 6H2O + energy

effects of bleaching events
Immediate effects

*Decrease in zoox density

*Loss of chlorophyll pigment

*Increase in respiration while decrease in zoox contribution of sugars

Long-term effects

*Decrease in coral growth

*Reproduction impairment

*Tissue necrosis

*Disruption of the reef and interdependent ecosystems

Effects of Bleaching Events
coral sensitivity
Coral Sensitivity
  • Coral reefs thrive in water temperatures no more than 29oC
  • Coral reefs are sensitive to the slightest changes in temperature
  • Small prolonged changes of 0.5-1.5oC may result in a bleaching event
  • Large temperature increases of about 3-4oC

may result in bleaching in a shorter amount of time

contributing factors to temperature related bleaching
Contributing factors to temperature related bleaching
  • Sudden drops in sea level exposing coral reefs
  • Reduced water circulation for cooling
  • Low cloud cover increasing solar irradiance
  • Large scale sea warming
  • Lower oxygen levels being dissolved in warmer water
difficulties in assessing degree of coral bleaching
Difficulties in assessing degree of coral bleaching
  • Genetic differences in zooxanthellae responsible for varying stress tolerance
  • Reaction of same species of zooxanthellae in different hosts
  • Reaction of different zooxanthellae species in same host
  • Varying amount of pigmentation between zooxanthellae
  • Article refers to extent of bleaching not quantitatively but qualitatively (mild or severe)
methods
Methods
  • Sea surface temperatures were taken dockside for thirty years at the time considered to be most like temperatures on the coral reef
  • Absolute temperature, cumulative heat stress (prolonged exposure to higher than normal temperatures), and rate of temperature change (temperature shock), were analyzed
  • Threshold temperature before bleaching occurs is unknown, therefore researchers tried to develop indices of annual temperature variation to predict bleaching events
conclusions
Conclusions
  • Sharp increases in temperature when temperatures are already near the annual maximum is a culprit in severe coral bleaching
  • Cumulative heat stress, or prolonged exposure to higher than normal temperatures also induce bleaching
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