Symbiosis between Zooxanthellae

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Symbiosis between Zooxanthellae Corals

• By
• Mark Mergler

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What are Zooxanthellae?

• Unicellular yellow-brown dinoflagellate algae
  which live in the gastrodermis of corals
• Provide corals with food in the form of
  photosynthetic products
• Live in corals tissues at a density of 1million
  cells/cm²
• Due to need for light, they only live in ocean
  waters lt100 m
• Recently found that there are 10 different
  species that live in corals

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http//www.seaslugforum.net/factsheet.cfm?basezoo
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http//plaza.ufl.edu/amb1685/Coral_Reef.html
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What are Corals?

• Start their lives as free-swimming young
• Once they find a hard bottom, they attach
  themselves and quickly change into a polyp
• Coral polyp splits in 2 and makes an identical
  copy of itself
• Form a colony and secrete a hard calcium
  carbonate skeleton
• Each polyp makes a small skeletal cup called a
  calyx which aids in feeding
• As coral colony grows, it secretes new skeletal
  material on top of the old
• Over thousands of years of accumulation, a coral
  reef is formed

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http//www.seasky.org/reeflife/sea2b.html
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Symbiotic Relationship between the Two

• Zooxanthellae
• Provide Corals with food in the form of organic
  matter
• Corals
• Provide zooxanthellae a safe place to live
• Excrement is taken in by dinoflagellates and are
  recycled

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Fringing Reefs

• Simplest most common type
• Develop near shore throughout tropics
• Occurring close to land makes them vulnerable to
  sedimentation, freshwater runoff, and human
  disturbance Consist of
• An inner reef flat
• An outer reef slope

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http//plaza.ufl.edu/amb1685/Coral_Reef.html
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Barrier Reefs

• Much further from shore than fringing reef
• Consist of
• A back-reef slope
• A reef flat
• A fore-reef slope
• Most coral growth occurs on the fore-reef slope

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http//plaza.ufl.edu/amb1685/Coral_Reef.html
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Atoll

• Ring of reef that form from sinking volcanoes
• Usually have a central lagoon
• Can rise up from depths of thousands of meters or
  more
• Occur mostly in the Indo-west Pacific region

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http//plaza.ufl.edu/amb1685/Coral_Reef.html
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Coral Bleaching

• Occurs when corals undergo stressful situations
• White calcium carbonate skeleton is exposed when
  corals expel their zooxanthellae
• Never a total elimination, (60-90) remain
• Is possible for corals to come back as long as a
  substantial amount of time has not passed
• Normal environmental conditions must return
• If conditions do not return, host corals will
  perish

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http//www.marinebiology.org/coralbleaching.htm
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http//www.marinebiology.org/coralbleaching.htm
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Climatic Change / Human Impact

• Climatic change
• Increase in temperature
• Violent weather
• Increased UV exposure
• Human impact
• Oil pollution
• Coral mining
• Overfishing
• Sedimentation
• Nutrient enrichment

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ReferencesBrown, B. E. 1997. Disturbances to
reefs in recent times. Pages 354-379 in Life and
Death of Coral Reefs, edited by C. Birkeland.
Chapman Hall, New York, NY.  Graham, Linda
E., and Lee W. Wilcox. Algae. Upper Saddle River,
NJ Prentice Hall, 2000.  Hughes, Terry P.
Climate Change, Human Impacts, and the
Resilience of Coral Reefs Science. 301.5635
(2003) 564-576. Muller-Parker, G., and C. F.
DElia. 1997. Interactions between corals and
their symbiotic algae. Pages 96-113 in Life and
Death of Coral Reefs, edited by C. Birkeland.
Chapman Hall, New York, NY. West, Jordan M.,
and Rodney V. Salm. Resistance and Resilience to
Coral Bleaching Implications for Coral Reef
Conservation and Management. Conservation
Biology. 17.4 (2003) 956-967.