The Crucial Symbiosis Between Zooxanthellae and Corals for Reef Health
This overview explores the vital relationship between zooxanthellae and corals, highlighting how these unicellular dinoflagellates are integral to coral survival. Living in coral tissues, zooxanthellae provide essential food through photosynthesis, while corals offer them a protective habitat. The text discusses various coral reef types, including fringing reefs, barrier reefs, and atolls, and addresses the alarming issue of coral bleaching due to environmental stressors. Understanding this symbiosis is critical for the conservation of coral reefs impacted by climate change and human activities.
The Crucial Symbiosis Between Zooxanthellae and Corals for Reef Health
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Presentation Transcript
Symbiosis between Zooxanthellae & Corals By Mark Mergler
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
http://www.seaslugforum.net/factsheet.cfm?base=zoox1 http://plaza.ufl.edu/amb1685/Coral_Reef.html
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
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
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
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
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
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
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.
