Coral%20Reefs

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29 April 2008OCN 621 Biological Oceanography

• Coral Reefs
• What is a coral reef?
• Habitat forming scleractinians
• Different types of reef
• Symbiosis
• Biogeography
• Controls on Biogeography
• The value of reefs

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What is a coral reef?

• Reef
• Feature lying beneath the surface of the water
  with which a boat could get stuck on
• Typically diverse assemblage of habitat forming
  scleractinians
• Mainly Shallow
• Butnot always
• Important engineers
• Biodiversity
• Rain forests of the ocean
• Cover less than 1/10 of ocean floor
• Habitat for 25 of all marine species

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What is a coral reef?

• Scleractinians (primarily)
• Other organisms also produce calcium carbonate
  structures
• Forminifera, cocolithophores, pteropods,
  halimeda, red algae, soft coral spicules, sponge
  spicules
• Reef structure is cemented together by calcareous
  red algae or by lithification
• Organisms creating non-carbonate skeletons
• Chitin, silica, gorgonin
• Octocorals, sponges

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Coral Reefs of the World

• Great Barrier Reef, Australia
• Largest coral reef in the world, 2600km
• Belize Barrier Reef
• Second largest in the world
• New Caledonia Barrier Reef
• Second longest double barrier reef 1500km
• Andros Barrier Reef
• 3rd largest barrier reef, 167km long and 64km
  wide
• Red Sea Coral Reef
• Egypt Saudi Arabia
• Pulley Ridge
• Florida, Deepest photosynthetic coral reef, 60m
  deep

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Scleractinian morphology

• Branching
• Often fast growing
• Plate-like
• Often found in deeper environments
• Massive/lobed
• Generally slower growing, k-selected
• Encrusting
• Sometimes parasitic

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Branching
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Plate Like
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Massive, Lobed
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Encrusting
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Types of Reef

• 4 Main types of reef
• Fringing, Barrier, Patch and Atoll
• Also Apron, Bank, Ribbon Table
• Fringing reef
• a reef that is directly attached to a shore or
  borders it with an intervening shallow channel or
  lagoon
• Bora Bora, French Polynesia

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Bora Bora
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Types of Reef

• Barrier Reef
• a reef separated from a mainland or island shore
  by a deep lagoon
• Great Barrier Reef - Australia

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Great Barrier Reef, Australia
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Types of Reef

• Patch Reef
• an isolated, often circular reef, usually within
  a lagoon or embayment
• Outer edge of each patch reef is surrounded by a
  halo of sand that extends out to adjacent
  seagrass beds.
• The width of this ring of sand is determined by
  the distance that herbivorous fish feel is within
  safe foraging range from the reef.
• Florida

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Types of Reef

• Atoll Reef
• a more or less circular or continuous barrier
  reef extending all the way around a lagoon
  without a central island
• Midway, Hawaiian Islands

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Midway
Maldives
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Atoll Formation

• Island erosion
• Island sinking
• Reef accretion

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Reef Zones
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Symbiosis

• Photosynthetic algal endosymbionts
• Dinoflagellates
• Algae located in gastrodermis
• Carbohydrates and lipids excreted by the algae
• Protection and nitrogenous waste provided by host
• Other marine taxa also engage in similar
  symbiosis
• Sea anemones, jellyfish, sponges, clams, forams
• Can provide up to 90 of corals energy

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Symbiosis
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Symbiosis

• Genus Symbiodinium
• Different species live in different corals
• Controversial
• Ingested by corals
• But not digested
• Reproduce by budding
• 3 Life Stages
• Vegatative
• Cyst
• Motile

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Shallow water coral biogeography

• Warm tropical climates
• Low latitudes (30ºN to 30ºS)
• High solar insolation
• Warm water currents
• Clear shallow waters
• good light penetration
• 30m
• low sedimentation and turbidity
• Oligotrophic waters
• nutrient poor but not exclusively
• Hard substrata

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Annual Pattern of Daily Solar Insolation
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Biogeography
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Biogeography

• What limits shallow coral reefs?
• High latitude and depth
• Temperature, chronic low temperature stress
• Light irradiance, insufficient solar insolation
• Aragonite (CaCO3) saturation state
• Competition with temperate fauna

Kleypas, 1999, Grigg, 2006
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Biogeography

• Distinct fauna between Atlantic and Indo-Pacific
• Lower diversity in the Atlantic
• Younger, smaller ocean basin with less thermal
  capacity
• North-south mountain ranges did not impede
  glacial advances during ice ages
• More extinction events
• But older coral genera 60 mya ?

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Biogeography
Modified from Spalding, M. et al. 2001
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Biogeography

• Higher diversity in the Indo-Pacific
• Older ocean basin with more stability through
  geological time
• Larger body of water with more thermal capacity
• East-west mountain ranges limited glacial
  advances during ice ages
• But younger coral genera 30 mya ?
• Center of diversity in the Indo-Australian
  Archipelago (IAA)
• Diversity gradient as radial distance from center
  increases

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Biogeography
Veron, 1995
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Reef Value

• Found in over 100 countries
• Over 500 million people worldwide rely on coral
  reefs
• Major source of food
• Poorer countries
• Fish and invertebrates
• Conch, bivalves, octopus, squid.
• Food for pelagic fish species
• Limestone
• Building materials, breakwaters, cement
• Jewelry
• Aquarium trade
• Tourists
• 6-10billion US tourist industry
• Beach protection
• Wave breaks

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Conclusions

• Majority of coral reefs are shallow, warm
  tropical, made from carbonate accreting species
• Majority have photosynthetic algae
• A reef can be in many different forms
• Limited in latitude and depth
• Higher diversity in the Indo Pacific
• Reefs are worth s