Coral Reefs

Introduction

• Calcium carbonate (CaCO3) anyone??

• Limestone is left over when animals grow and die.

• This carbon containing molecule is the basis for coral formation.

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

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

Coral Types:

• Hard (Stony, scleractinian, “true”) corals build the 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.

What is Coral?? Animal, Vegetable, Mineral?

Rem: Coral are actually a special group of cnidarians, the same family as jellyfish!!

Hermatypic vs. Non-Hermatypic Corals

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

• Ahermatypic Corals (b): Corals that are solitary or form small colonies (often lack zooxanthellae and do not help build reefs).

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

Coral larva are called planula, since they don’t like soft sea floors, they often metamorphose into a polyp which establishes a founder colonyfounder colony in a new location.

Boulder coral Montastrea cavernosa

Medusa’s are a mobile polyp.

Coral remain closely connected.

Zooxanthellae, single-celled photosyntheticalgae work within the coral to help feed itthrough photosynthesis.

As a result of this symbioticrelationship, many coralsdon’t need to seek food.

This added nutrition also helps corals to build reefsmuch faster!

microscopic view of zooxanthellae)microscopic view of zooxanthellae)

Mutualism Between Corals and Zooxanthellae

• Coral Polyp

• Provides a home for the zooxanthellae.

• Provides nitrates and phosphates.

• Gives off CO2.

Here is a good example of a live coral.

Obviously, the one on the left needs help!!

Coral take on many shapes!!

Reefs grow when calciumcontaining sediments are deposited in spaces between coral.

As encrusting coraline algae “glues” the sediments together,new “live rock” is formed.

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.

Coral exhibit limited range in growth patterns.

Without proper light and temperature,coral dies (bleaches).

It only takes 1-2 degrees in some cases.

How does global warming effect this trend?

From this…

To this….

Temperature increases and competition from red algae have killed much of this coral reef.

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.

Fringe Reefs: Diving anyone??

Growth on reefs are often limited by tidal action.

Disease is another major factor limiting growth. Here is an example of elkhorn coral (Acropora palmata) infested by “white band disease.”

Barrier Reefs

An excellent example of a Pacific barrier reef.

Barrier reef structure can be influenced by spur and groove formations such as these.

The Great Barrier Reef

Atoll Reefs: Volcanic Left-overs!

Atoll Reef Fulanga

Atoll Formation: Step by step

Reef Ecology: Edge effect again…

Food Webs: Same concept, more complexity

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!

Again, we see that real estate is at a premium with these soft corals. Soft corals are fast growers, making them excellent competetors.

Harmony? Not really, most animals on reefs compete daily for everything, from food to mating opportunities.