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Lecture 21

01:460:120 Lecture 21: Lecture 21 - Coral Reefs

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Geological Sciences

Coral Reefs Key Concepts  Corals first appeared in the fossil record over 400 million years ago  Corals evolved into more "modern" reef-building, colonial forms about 25 million years ago  Coral reefs are the largest structures on earth that result from biological activity  Most coral reefs go through 3 stages of development: o Fringing reef o Barrier reef o Atoll  Coral reefs are complex ecosystems; although they cover <1% of the ocean bottom, they are the home of 25 % of all marine life  The prodigious productivity of coral reefs is due to symbioses between unicellular autotrophic algae (zooxanthellae) and coral  Corals are related to sea anemones and jellyfish  There are two groups of corals; o Stony corals o Soft corals  Stony corals are the group responsible for building up reefs, they do this by secreting calcium carbonate, CaCO 3  For the most part, stony corals are colonial organisms composed of hundreds to hundreds of thousands of small individuals, called polyps, which are typically only 1-3mm in diameter Anatomy of a Coral Polyp Anatomy of a Coral's Stinging Cell  Used for: o Capturing zooplankton prey o Fighting with other coral species  Corals have a symbolic relationship with unicellular algae  Zooxanthellae are tiny symbiotic dinoflagellates  Coral's success in nutrient poor water depends on this relationship  Coral: provide protected environment, compounds necessary for photosynthesis (carbon dioxide, metabolic wastes containing nitrogen and phosphorus)  Zooxanthellae: absorb waste products, produce oxygen, sugars, amino acids This symbiosis is the key to the prodigious productivity of coral reefs   Up to 90% of the organic matter zooxanthellae produce is transferred to host coral The pigments in zooxanthellae can determine the color of the coral polyps From polyp to reef Living coral showing outer Underlying skeletal covering of tissue structure composed of calcium carbonate  Colonies of reef-building corals show a wide range of shapes o Branching  o Digitate  o Tabl
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