Bleaching: Difference between revisions

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== What is bleaching?==
== What is bleaching?==
Simply, it is the release of coral symbiotic zooxanthellae. A more in depth definition is the loss of all or some symbiotic algae and photosynthetic pigments by the coral animal resulting in their white calcium carbonate skeleton becoming visible through the now translucent tissue layer making them appear white or ‘bleached’ of their original color <ref name=bleach> H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1 </ref> <ref name=Tyrrell>T. Tyrrell (2007). Calcium Carbonate Cycling in Future Oceans and its Influence on Future Climates.</ref>
Simply, it is the release of coral symbiotic zooxanthellae. A more in depth definition is the loss of all or some symbiotic algae and photosynthetic pigments by the coral animal resulting in their white calcium carbonate skeleton becoming visible through the now translucent tissue layer making them appear white or ‘bleached’ of their original color <ref name=bleach> H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1 </ref> <ref name=Tyrrell>T. Tyrrell (2007). Calcium Carbonate Cycling in Future Oceans and its Influence on Future Climates.</ref>
Coral bleaching may occur when the thermal tolerance of the coral's photosynthetic symbionts, known as zooxanthellae , or the coral itself is exceeded.
* Corals and symbiotic relationship
*There are two classifications of coral species concerning zooxanthellae: zooxanthellate and azooxanthellate. Zooxanthellate corals are found covering much of the shallow water reefs in tropical regions. Corals that can survive under both classifications are extremely rare.  
*There are two classifications of coral species concerning zooxanthellae: zooxanthellate and azooxanthellate. Zooxanthellate corals are found covering much of the shallow water reefs in tropical regions. Corals that can survive under both classifications are extremely rare.  
**Scleractinian corals provide an example of common zooxanthellae symbiosis. <ref name=bleach> H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1 </ref>
**Scleractinian corals provide an example of common zooxanthellae symbiosis. <ref name=bleach> H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1 </ref>
* Corals and symbiotic relationship
** What are zooxanthellae?  
** What are zooxanthellae?  
***Dinoflagellates of the genus Symbiodinium that live in coral tissues <ref name=bleach> H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1 </ref>
***Dinoflagellates of the genus Symbiodinium that live in coral tissues <ref name=bleach> H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1 </ref>

Revision as of 18:24, 15 April 2013

Coral Bleaching

What is bleaching?

Simply, it is the release of coral symbiotic zooxanthellae. A more in depth definition is the loss of all or some symbiotic algae and photosynthetic pigments by the coral animal resulting in their white calcium carbonate skeleton becoming visible through the now translucent tissue layer making them appear white or ‘bleached’ of their original color [1] [2] Coral bleaching may occur when the thermal tolerance of the coral's photosynthetic symbionts, known as zooxanthellae , or the coral itself is exceeded.

  • Corals and symbiotic relationship
  • There are two classifications of coral species concerning zooxanthellae: zooxanthellate and azooxanthellate. Zooxanthellate corals are found covering much of the shallow water reefs in tropical regions. Corals that can survive under both classifications are extremely rare.
    • Scleractinian corals provide an example of common zooxanthellae symbiosis. [1]
    • What are zooxanthellae?
      • Dinoflagellates of the genus Symbiodinium that live in coral tissues [1]
      • There are various clades (or group of organisms derived from a common ancestor) that live in different corals, and some of these species are more resistant to bleaching than others.
      • The relationship between zooxanthellae and corals is thought to have evolved from a single adaptive radiation event, however the different species or clades of symbionts that live together in the same coral as well as at different depths and light intensities complicates the simple idea of co-evolution with their host. Corals can gain zooxanthellae through the environment and/or from the parent colony. [1]
    • What do they do? Why are zooxanthellae important?
      • They provide energy for the coral animal through photosynthesis. It gives the coral the nutrients needed to create the foundational calcium carbonate skeleton.
      • They remove excess carbon dioxide which interferes with skeleton formation
      • The ability to rapidly create these calcified skeletons and the metabolic advantages from the photosynthesis allow zooxanthellae scleractinian corals to grow quickly and construct dominant reefs in tropic waters. [2]
  • Expulsion of zooxanthellae
    • The zooxanthellae give the corals color their color. When the relationship becomes toxic and the zooxanthellae are released, the coral becomes transparent and appear white as a result of their calcium carbonate backbone structure showing through.

Causes

  • SST
    • Stress on corals
    • Affects on symbiotic relationship
    • Past, present, and future predictions/ frequency of bleaching events [3]
  • Acidification [4]
    • What is acidification?
      • Carbon dioxide dissolves in the ocean and increases ocean acidity or decreases the ocean pH. This dissolves the calcium carbonate (CaCO3) which makes up the coral skeleton
    • Impact of acidification on bleaching – increases bleaching events
    • Synergy with SST
      • Higher SST amplifies acidification effects and bleaching events
  • Stress
    • Types
      • Elevated temperature
      • High solar irradiance
      • Disease
      • Hostile/changing environment
    • Disruption of symbiotic relationship
      • Why expel zooxanthellae?

caption NOAA Coral Reef Watch near- real-time satellite from 2205 showing a.SST b.SST anomalies c.coral bleaching HotSpots d. coral bleaching Degree Heating Weeks[1]

Effects

  • Disease – frequency increases
  • Ecosystem/reef effects
    • Corals – productivity, recruitment, survivability/adaptation
    • Fish/Other organisms – habitat, recruitment, abundance

"Fig. 3. Ecological feedback processes on a coral reef showing pathways of disturbance caused by climate change. Impact points associated with ocean acidification (e.g., reduced reef rugosity, coralline algae) are indicated by the blue arrows, and impact points from global warming (e.g., bleached and dead corals) by the red arrows. Boxes joined by red arrows denote that the first factor has a negative (decreasing) influence on the box indicated. Green arrows denote positive (increasing) relationships. Over time, the levels of factors in hexagonal boxes will increase, whereas those in rectangular boxes will decline. Boxes with dashed lines are amenable to local management intervention."[5]

Special Case Study

  • US Virgin Islands: Bleaching 2005
    • In the summer of 2005, unusually calm seas and record setting warm seawater temperatures induced the most devastating coral bleaching ever recorded in the U.S. Virgin Islands (USVI) with coral cover being more than 90% bleached and stretching from the surface to 20 meters deep. [6]
    • This weather shock was followed by a breakout of disease on the reefs, which led to increase monitoring, but more partial or total coral death in the USVI.
    • Two corals that create much of the framework of reefs in USVI were heavily affected: Acropora palmata and Montastraea annularis.[6]
      • Montastraea annularis, while remaining very present on the reefs, dropped from 55.6 percent to 40.9 percent of coral cover over the 2 years following the bleaching event
      • Acropora palmate was less affected by disease, but 50% of the corals being watched in 2005 showed signs of bleaching, marking the first record of A, palmate bleaching in the USVI.
    • Researchers showed a correlation between temperature and disease, but only with the 2005 massive bleaching event. They found the size of white syndrome lesions, like white pox, increased as temperature increased for bleached colonies, but not other healthy colonies. [6]
    • Even with cooler temperatures, the coral cover continued to decline, with the mean coral cover decreasing 61% through 2007. At peak disease after bleaching, “the mean number of lesions increase 51-fold and the mean area killed by disease increase 30 fold” in reference to levels prior to the bleaching event. [6]
      • This is the only study to show such extreme declines in coral cover from disease covering such a large area. [6]
  • Sunscreen and reefs
    • It has been proven that sunscreen and other personal care cosmetics are potentially harmful to marine environments in terms of bioaccumulation of UV filters in animals and photodegradtion, which turns sunscreen agents into toxic by-products. They can be so harmful that they have been banned in certain high tourists areas, but there had been no studies on the effect on reefs
    • In a study headed by faculty at Polytechnic University of the Marche, Ancona, Italy, researchers measured the effect of sunscreen on reefs from 2003-2007.
    • A team conducted experiments adding aliquots of sunscreens and other common ultraviolet filters contained in sunscreen to the coral branches from several different tropical areas covering the Pacific, Atlantic, Indian, and Pacific Ocean plus the Red Sea. Then, they observed the zooxanthellae for viral infection. [7]
    • Through these experiments on site and in the laboratory, it was determined that sunscreens cause complete and rapid bleaching of hard corals, even at extremely low concentrations. This negative effect is the result of organic ultraviolet filters, which cause zooxanthellae with infections to enter a lytic viral cycle. By fostering this viral infection, sunscreens could play a influential role in coral bleaching in areas exposed to high levels of human recreation. [7]
    • It was calculated that 10% of the reefs in the world could be threatened by sunscreen induced bleaching. This calculation is a result of the estimations that in tropical countries somewhere between 16,000 and 25,000 tons of sunscreens will be applied, and of that amount at least 25% will be washed off in the ocean. This leads to a potential release of 4,000–6,000 tons/year of sunscreen in reef areas. This number will only increase as humans continue to increase our use of the reefs. [7]

caption An example of bleached coral due to the effects of sunscreen. [7]

caption A data table showing the results of the experiments on various hard corals with sunscreens and sunscreen ingredients [7]

What we are currently doing to sustain coral ecosystems

  • USGS “Science Based Strategies” example
    • Coral reefs are necessary in supporting many different ecosystems and populations, but these marine ecosystems and all the benefits that come with them are at risk. Scientific evidence continues to show that the threat to coral reefs is serious, and could cause severe large scale social and ecological consequences if not addressed.
    • Although several threats and stressors are known, there are still strides that need to be made in how scientists respond to and explain both natural and human influenced changes in reef ecosystems. Science needs to improve how we respond to and/or prevent the current problems such as carbon sequestration, ocean temp, ocean acidification, sea level rise, atmospheric dust, land-derived impacts, pathogens and disease, overfishing and ecological integrity [8]
    • For more information see Protecting and Managing Coral Reefs


Notes

  1. 1.0 1.1 1.2 1.3 1.4 H. van Oppen, M. J., & Lough, J. M. (2009). Coral bleaching: Patterns, processes, causes and consequences. (Vol. 205). Springer Berlin Heidelberg. Retrieved from http://link.springer.com/book/10.1007/978-3-540-69775-6/page/1
  2. 2.0 2.1 T. Tyrrell (2007). Calcium Carbonate Cycling in Future Oceans and its Influence on Future Climates.
  3. Hoegh-Guldberg, Ove (1999) . Climate change, coral bleaching and the future of the world's coral reefs. Marine and Freshwater Research 50 , 839–866.
  4. K.R.N. Anthony, et al. (2008). Ocean acidification causes bleaching loss in coral reef builders. PNAS vol. 105 no. 45.
  5. O. Hoegh-Guldberg, et al. (2007). Coral Reefs Under Rapid Climate Change and Ocean Acidification. Science 318, 1737.
  6. 6.0 6.1 6.2 6.3 6.4 USGS. (2008, June). Coral diseases following massive bleaching in 2005 cause 60 percent decline in coral cover and mortality of the threatened species, acropora palmata, on reefs in the u.s. virgin islands. Retrieved from http://pubs.usgs.gov/fs/2008/3058/pdf/fs2008-3058.pdf Cite error: Invalid <ref> tag; name "USGS" defined multiple times with different content Cite error: Invalid <ref> tag; name "USGS" defined multiple times with different content
  7. 7.0 7.1 7.2 7.3 7.4 Danovaro, R., Bongiorni,, L., Corinaldesi, C., Giovannelli, D., Pusceddu, A., Damiani, E., Astolfi, P., & Greci, L. (2008). Sunscreens cause coral bleaching by promoting viral infections. Environmental Health Perspectives, 116(4), 441-447.
  8. USGS. (2008, September). Science-based strategies for sustaining coral ecosystems. Retrieved from http://pubs.usgs.gov/fs/2009/3089/pdf/brewercoralfs3.pdf
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