Symbiosis between Zooxanthellae & Corals

By

Mark Mergler

What are Zooxanthellae?Unicellular yellow-brown dinoflagellate algae which live in the gastrodermis of coralsProvide corals with food in the form of photosynthetic productsLive in coral’s tissues at a density of 1million cells/cm² Due to need for light, they only live in ocean waters <100 mRecently found that there are 10 different species that live in corals

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

http://www.seaslugforum.net/factsheet.cfm?base=zoox1

What are Corals?Start their lives as free-swimming youngOnce they find a hard bottom, they attach themselves and quickly change into a polypCoral polyp splits in 2 and makes an identical copy of itselfForm a colony and secrete a hard calcium carbonate skeletonEach polyp makes a small skeletal cup called a calyx which aids in feedingAs coral colony grows, it secretes new skeletal material on top of the oldOver thousands of years of accumulation, a coral reef is formed

http://www.seasky.org/reeflife/sea2b.html

Symbiotic Relationship between the Two

ZooxanthellaeProvide Corals with food in the form

of organic matter

CoralsProvide zooxanthellae a safe place to

liveExcrement is taken in by

dinoflagellates and are recycled

Fringing Reefs

Simplest & most common typeDevelop near shore throughout tropicsOccurring close to land makes them vulnerable to sedimentation, freshwater runoff, and human disturbance Consist of An inner reef flat An outer reef slope

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

Barrier Reefs

Much further from shore than fringing reefConsist ofA back-reef slopeA reef flatA fore-reef slope

Most coral growth occurs on the fore-reef slope

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

Atoll

Ring of reef that form from sinking volcanoesUsually have a central lagoonCan rise up from depths of thousands of meters or moreOccur mostly in the Indo-west Pacific region

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

Coral Bleaching

Occurs when corals undergo stressful situationsWhite calcium carbonate skeleton is exposed when corals expel their zooxanthellaeNever a total elimination, (60-90%) remain Is possible for corals to come back as long as a substantial amount of time has not passedNormal environmental conditions must returnIf conditions do not return, host corals will perish

http://www.marinebiology.org/coralbleaching.htm

http://www.marinebiology.org/coralbleaching.htm

Climatic Change / Human Impact

Climatic change Increase in temperature Violent weather Increased UV exposure

Human impact Oil pollution Coral mining Overfishing Sedimentation Nutrient enrichment

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. D’Elia. 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.