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Coral Reefs

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Introduction

• Calcium carbonate (CaCO3) anyone??

• Limestone is left over when animals grow anddie.

• This carbon containing molecule is the basis forcoral formation.

• As we will see, coral production exhibits hugeimpacts on ecosystem diversity and success.

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Requirements for Reef Formation

• High Light Levels

• High Water Transparency

• Water Temperatures > 20°C (68°F)

• Low Nutrient Waters

• Hard Substrate for Attachment

• Good water circulation

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Coral Types:

• Hard (Stony, scleractinian, “true”) corals buildthe reef by extracting calcium carbonate from the

ocean water.

• They create a home in which primary producers

can live.

• They create a diverse 3-D space in which many

other organisms can find homes.

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What is Coral?? Animal, Vegetable, Mineral?

Rem: Coral are actually a special group of cnidarians, the

same family as jellyfish!!

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Hermatypic vs. Non-Hermatypic Corals

• Hermatypic Corals (a): Corals that form largecolonies called reefs.

• Ahermatypic Corals (b): Corals that are solitaryor form small colonies (often lack zooxanthellae

and do not help build reefs).

a. brain coral ( Diploria)  b. Mushroom coral ( Fungia)

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Coral larva are called planula, since they don’t like soft

sea floors, they often metamorphose into a polyp which

establishes a founder colony in a new location.

Boulder coral Montastrea cavernosa

Medusa’s are a mobile polyp. 

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Coral remain closely connected.

Zooxanthellae, single-celled photosynthetic

algae work within the coral to help feed it

through photosynthesis.

As a result of this symbiotic relationship, many corals

don’t need to seek food. 

This added nutrition alsohelps corals to build reefs

much faster!

microscopic view of zooxanthellae)

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Mutualism  Between Corals and Zooxanthellae

• Coral Polyp

• Provides a home for the zooxanthellae.

• Provides nitrates and phosphates.

• Gives off CO2. 

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Here is a good example of a live coral.

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Obviously, the one on the left needs help!!

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Coral take on many shapes!!

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Reefs grow when calcium

containing sediments aredeposited in spaces between coral.

As encrusting coraline algae

“glues” the sediments together, 

new “live rock” is formed. 

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Once this Halimeda(calcareous green algae) dies, 95%

of what remains will be sediment and real estate for new

coral colonies.

Coral benefits from the death of other organisms.

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Coral exhibit limited range in growth patterns.

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Without proper

light and temperature,coral dies (bleaches).

It only takes 1-2 degrees

in some cases.

How does global warming

effect this trend?

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From this… 

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To this…. 

Temperature increases and competition from red algae have killed

much of this coral reef.

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Coral Reefs Have High Primary Productivity

• Coral Reef primary production ranges from 1500

to 3700 g of C/m2/yr.

• This makes Coral Reefs one of the most

 productive communities on earth!

• Rapid nutrient cycling between zooxanthellae and

corals may be partially responsible for this.

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Fringe Reefs: Diving anyone??

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Growth on reefs are often limited by tidal action.

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Disease is another major factor limiting growth. Here is

an example of elkhorn coral ( Acropora palmata) infested

 by “white band disease.” 

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Barrier Reefs

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An excellent example of a Pacific barrier reef.

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Barrier reef structure can be influenced by

spur and groove formations such as these.

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The Great Barrier Reef

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Atoll Reefs: Volcanic Left-overs!

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Atoll Reef Fulanga

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Atoll Formation: Step by step

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Reef Ecology: Edge effect again… 

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Food Webs: Same concept, more complexity

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Coral Fights??

Yes!

Just like other animals competing for space, coral attack

each other if they come into close contact.

Usually they just over grow one another, but some actually

poison the others out!

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Again, we see that real estate is at a premium with these

soft corals. Soft corals are fast growers, making them

excellent competetors.

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Harmony? Not really, most animals on reefs

compete daily for everything, from food to mating

opportunities.