Coral Reefs and Lagoons

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Part I
Section 5


Invertebrate marine animal
A polyp that begins to form an exoskeleton
◦ CO2 & Ca in the water to make calcium carbonate
(CaCO3) aka limestone


Sessile – immobile
Form colonies
Coral atolls
 1st 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 1st map of
distribution of corals
3 main types:
◦ Fringing barrier reefs, barrier reefs, atolls

Conditions required:
◦ Temperature range =16⁰C – 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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be
What’s going
on here?

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)
Egypt (Red Sea)
Baja


Due Friday!
Read Marine Biology book pages 10-1
◦ Answer question 1 AND write bolded words with
definitions!
◦ Dropbox it in complete sentence(s)

Your NEW Oceanography textbooks are in!!!!!
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