Corals

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• Corals
• Biology
• Phylum Cnidaria, Class Anthozoa
• Lack medusa stage
• Hermatypic (reef building) corals produce
  skeletons made of calcium carbonate
• Some hermatypic corals are in Class Hydrozoa
  (fire corals)

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• Corals
• Biology
• Many corals are ahermatypic
• Ex - Soft corals, sea fans, gorgonians, black
  corals
• Most hermatypic corals contain symbiotic
  zooxanthellae
• Zooxanthellae enhance rate of calcium carbonate
  deposition (growth)
• Relationship Mutualism
• Corals have many growth forms

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• Corals
• Biology
• Reproduction
• Sexual - Polyp --gt Planula (planktonic larva) --gt
  Polyp
• Asexual - Fragmentation
• All polyps in a colony genetically identical

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• Coral Reefs
• Distribution
• Living reefs 600,000 km2 (0.17 of sea floor)
• Great Barrier Reef Largest
• gt2000 km long
• Up to 145 km wide
• Visible from space

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• Coral Reefs
• Conditions
• Substrate
• Reefs occur primarily in areas with hard
  substrate
• Light - Bright (Why?)
• Reefs rarely develop in water gt 50 m deep
• Reefs located on continental shelves, around
  islands, on tops of seamounts
• Temperature
• Reefs limited to water with mean temperature gt 20
  oC

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• Coral Reefs
• Conditions
• Temperature
• Water that is too warm also is problematic
• Can cause bleaching and eventually death
• Bleaching events often occur during periods of
  unusually warm water
• Extreme low tide
• El Niño event
• Corals live near their upper thermal tolerance
  levels
• Corals from warmer waters have higher thermal
  tolerance levels

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• Coral Reefs
• Conditions
• Salinity
• Reefs tend to be absent or poorly developed near
  mouths of rivers
• Sediments
• Turbidity reduces light levels
• Sediments can smother corals
• Pollution
• Corals sensitive to pesticides and other
  chemicals
• Fertilizers can support growth of algae that
  smother corals
• Most corals grow in areas with low nutrient
  levels
• Tidal Regime
• Most corals cant tolerate prolonged periods of
  exposure

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• Coral Reefs
• Formation
• Corals are important components of reefs
• Other organisms also contribute
• Coralline red algae produce skeletons of calcium
  carbonate
• More important in Pacific than Atlantic
• Inhibit damage and erosion
• Algal ridge
• Cement sediments and rubble together

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• Coral Reefs
• Types
• 1-Atoll

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• Coral Reefs
• 2 - Fringing
• Simplest, most common type of reef
• Occur near shore throughout tropics
• Form narrow band (fringe) along shoreline
• Proximity to land makes fringing reefs especially
  vulnerable to sedimentation, freshwater runoff,
  and human influence
• Structure
• Reef flat
• Reef crest
• Reef slope

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Fringing Reef
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• Coral Reefs
• 2 - Fringing
• Reef flat
• Sheltered portion of reef
• Widest part of reef (few tens to few thousand
  meters)
• Shallow - Sometimes exposed at low tide
• Bottom primarily sand, mud, or coral rubble
• Sea grasses, soft corals, benthic algae common
• Reef crest (Algal ridge - Pacific)
• Often experiences heavy wave action
• Highest point of reef
• Typically exposed at low tide
• Dominant species massive corals, resistant
  algae
• Richest coral growth (plenty of light, low
  sedimentation)
• Reef slope
• May be very steep
• Densest cover most species of coral
• Steep slope and good water flow provide oxygen
  zooplankton and carry away sediments wastes

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• Coral Reefs
• 3 - Barrier
• Not always obviously distinct from fringing reefs
• Generally occur farther from shore (up to 100
  km)
• Lagoon
• May contain patch reefs
• Back-reef slope
• Reef flat
• Waves and currents may pile up sand into sand
  cays (keys)
• Reef crest
• Fore-reef slope
• Often include spur-and-groove (buttress)
  formations (also found on atolls and some
  fringing reefs)

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Barrier Reef
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Reef Zonation
Form of reef builders dependent on physical
agitation, light availability and sedimentation
rate
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A sketch illustrating the three major reef facies
in cross section.
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A sketch of the four division of the reef core
facies with a tabulation of the most common types
of limestone, relative species diversity and
shape of reef builders found in each stage.
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Reefs Through Time
Note The dominant reef-builders and
reef-dwellers have changed through time as a
result of extinction and evolution
Probably all powered by photosynthesis
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Precambrian (Archaean to Proterozoic) Dominant
Reef Builders Cyanobacteria
Stromatolite mound of Proterozoic age Kuuik
Formation, Kilohigok Basin, Northwest
Territories
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Cambrian
Dominant Reef Builders Archaeocyathans
(sponges) and skeletal algae
Cross section of Archaeocyathan sponge
Reef in Newfoundland
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Ordovician-Silurian Mostly mudmounds (dominated
by algae, bryozoa and microbes)
Stromatactis, sub-horizontal layers of calcite
spar illustrating irregular digitate tops and
smooth bottoms, from Gros Morne, reefmound
facies, Silurian West Point reef complex, Gaspé,
Quebec. Possibly due to cyanobacterial decay
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Devonian Dominated by stromatoporoids (sponges)
and corals
Encrusting stromatoporoids
The diversification stage of an Upper Devonian
reef, comprising domal stromatoporoids, and domal
to branching tabulate corals, Blue Fjord
Formation, south side of Eids Fjord, Ellesmere
Island, N.W.T.
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Carboniferous-Permian Dominated by algae, bryozoa
(many mud mounds)
Muleshoe bioherm, a 60 m high reef mound of Late
Mississippian age exposed along the western
escarpment of the Scaremento Mountains, New
Mexico.
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A well-developed Permian reef El Capitan in
Guadalupe Mountains, New Mexico/Texas
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Triassic-Jurassic Dominated by stromatoporoids,
other sponges and few corals
corals
sponges
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Cretaceous Dominated by rudists and corals
Rudists bizarre reef-building clams !
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Cenozoic (both Paleocene and Neogene) Dominated
by corals
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• THE END