Symbiosis between Zooxanthellae & Corals

1. Symbiosis between Zooxanthellae & Corals By Mark Mergler

2. 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 coral’s tissues at a density of 1million cells/cm² • Due to need for light, they only live in ocean waters <100 m • Recently found that there are 10 different species that live in corals

3. http://www.seaslugforum.net/factsheet.cfm?base=zoox1 http://plaza.ufl.edu/amb1685/Coral_Reef.html

4. 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

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

6. 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

7. 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

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

9. 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

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

11. 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

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

13. 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

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

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

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

17. 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.