Coral Reefs

Introduction

• Limestone is left over when animals grow and die.

• Calcium carbonate 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)

• Hard Substrate for Attachment

• Good water circulation

Coral :

• Hard (Stony, true) corals build the reef by extracting calcium carbonate from the ocean water.

• They create a home in which primary producers can live.

What is Coral?? Animal, Vegetable, Mineral?

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 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.

– Zoox helps coral eat and get more sunlight

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 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.

3 types of Coral Reefs

• Fringing reefs- The most common type of reef, grows seaward directly from the shore. They form borders along the shoreline and surrounding islands.

• Atoll reefs- form from fringing reefs built on a sunken volcanic island. Usually circular or oval in shape, with an open lagoon in the center.

• Barrier reefs- are similar to fringing reefs in that they also border a shoreline; however, instead of growing directly out from the shore, they are separated from land by an expanse of water. This creates a lagoon of open, often deep water between the reef and the shore.

Fringing Reefs- 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.

The Great Barrier Reef

Atoll Reefs: Volcanic Left-overs!

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!

Soft corals are fast growers, making them excellent competitors.

Is there perfect harmony on reefs? Not really, most animals on reefs compete daily for everything, from food to mating opportunities.