 Invertebrate marine animal  A polyp that begins to form an exoskeleton ◦ CO 2 & Ca in the water to make calcium carbonate (CaCO 3 ) aka limestone  Sessile – immobile  Form colonies

Coral atolls  1 st proposed by Charles Darwin ◦ HMS Beagle (Nov 1835 – Apr 1836)  Supported and modified by 2 geologists ◦ James Daly ◦ Reginald Dana

1. Oceanic volcano emerges from sea surface and forms an island ◦ Colonized by reef-building corals

2. Growth of corals forms a fringing reef around the island ◦ Fringing reef – coral structure attached to the mainland or continental islands  Island begins to sink slowly  Coral growth continues

3. Island continues to sink  Barrier reef forms with lagoon around reef and island ◦ Barrier reef - reef separated from a mainland or island shore by a deep channel or lagoon

4. Island eventually disappears below sea surface  Atoll - consists of a ring of small islands  Shallow lagoon in center

Fringing reef can take 10,000 years to form Atolls up to 30 my Coral – tan and purple

 Data from deep drilling on coral atolls ◦ Bikini Atoll (Pacific Ocean) ◦ As depth of corals increased, age of corals also increased ◦ Fossil corals dated 50 myo and found 1200 m deep  Grown on underlying volcanic rock ◦ Shallow corals found at deep depths!

 Darwin (1842) produced 1 st map of distribution of corals  3 main types: ◦ Fringing barrier reefs, barrier reefs, atolls

 Conditions required: ◦ Temperature range =16 ⁰C – 35 ⁰C  Optimum range = 23 ⁰C - 25 ⁰C ◦ Water clarity  Clear water (less turbid) without silt  Silt reduces light penetration which inhibits photosynthesis of symbiotic zooxanthellae in coral tissues (90% nutrients provided)  Depth – rapid growth occurs within 20 m from surface ◦ Salinity ◦ Substrate – surface on which plant/animals live  Basaltic rocks of seamounts

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Zooxanthellae in Coral Polyp

Zooxanthellae: Symbiodinium microadriacticum

A Solitary Coral Polyp

Colonial Coral Polyps

Benefits to the Algal Symbiont Zooxanthellae gets a place to live Receive chemical wastes from animal metabolism (CO 2 & NH 3 ). Surrounding animal tissues can concentration substantial amounts of ultraviolet light absorbing compounds.

Benefits to the Coral Host Higher rates of calcification (skeleton deposition). Receive DOM & O 2 Removal of chemical wastes from animal metabolism (CO 2 & NH 3 ). Receive chemicals that absorb damaging ultraviolet light (Micosporine-like amino acids (MAAs)).

What’s going on here?

Distribution of Coral Reef Communities

 Shoreline protection from erosion - ◦ Dissipates/absorbs energy of waves  Benefits include protection of ◦ Coastal properties ◦ Ecosystems ◦ Costs to provide breakwaters – constructed structures for protection from erosion ◦ Anchorage of boats

 Coral Gardens Fiji (Pacific Ocean) Coral Gardens Fiji (Pacific Ocean)  Egypt (Red Sea) Egypt (Red Sea)  Baja Baja