Coral Reefs: Part 1

1. How is each reef structure formed?

Coral reefs begin to form when free-swimming coral larvae attach themselves to submerged rocks or other hard surfaces along the edges of islands/continents. As the corals grow and expand, reefs take on one of three major characteristic structures —fringing, barrier or atoll.

• Fringing reefs, which are the most common of all reefs, project seaward directly from the shore, forming borders along the shoreline and surrounding islands. Fringing reefs also grow on soft bottoms if there is even a small hard patch that lets the corals get a foothold. From there, the corals slowly creates their own hard bottom and expand themselves.
  
• Barrier reefs also border shorelines, but at a greater distance - sometimes as far as 100km. They are separated from their adjacent land mass by a lagoon of open, often deep water. The barrier reef consists of a back-reef slope, a reef flat, and a fore-reef slope, which corresponds to the reef slope of a fringing reef and has a reef crest.
• If a fringing reef forms around a volcanic island that subsides completely below sea level while the coral continues to grow upward, an atoll forms. Atolls range in size from small rings less than a mile across to systems well over 30 km in diameter.

2. Where is each reef structure found?

• Fringing reefs are found on rocky shorelines close to land.
• Barrier reefs, like fringing reefs, are found along the coast but farther out and separated by a lagoon.
• Atolls are found on top of sunken volcanic islands which lie underneath a layer of calcium carbonate.

3. What is the trophic structure of a reef?
The trophic structure of reefs revolves around nutrient recycling - which is basically zooxanthellae dependent since they are the dominant primary producers in the ocean. They take the coral nitrogen and phosphorus waste products and use the sun to create organic compounds which the corals need to survive. Without this process, corals would not be able to grow to their vast sizes since the water is usually poor in nutrients.

4. How does the location and type of reef influence the trophic structure?
Fringing reefs are close to shore so the water in which they live in gets runoff of a mixture of nutrients and pollution from the land. Barrier reefs, however, are farther out so they have access to water from the lagoon and the deeper ocean. Additionally, the fish and other organisms that live in the reefs add and subtract from the nutrients in that community.

5. Give examples of the types of corals found on reefs.
Common Name:

Branching Corals

Scientific Name:

Acropora Sp.

Type of Reef found on:

Reef Flat

Key Identification:

Stick like appearance & branching,

usually in colonies

6. Give examples of competition, predation, and grazing
Competition is an overgrowth or direct attack of one coral to another in their fight for growing space. A Crown-of-Thorns starfish is an example of predation since it eats and completely kills coral. Many types of fish eat coral polyps, but they don't eat enough to kill the whole organism. Grazing keeps coral populations in check.

Critical Thinking

Chapter 14

1. What factors might account for the fact that the vast majority of atolls occur in the Indian and Pacific oceans and that atolls are rare in the Atlantic?

Since corals are temperature dependent and nutrient dependent, they would most likely be found in the Indian and Pacific Oceans. Besides that, because of the Ring of Fire's location in the Pacific Ocean, atolls only be found there.

2. Scientists predict that the ocean will get warmer and the sea level will rise as a result of an intensified greenhouse effect. How might this affect coral reefs?

Disastrous effects may happen due to the amount of green house gases released. With a huge amount of CO₂ released into the atmosphere, it not only destroys the ozone layer, which would allow infrared heat to get trapped in the Earth’s atmosphere, causing the polar regions to melt thus allowing the sea level to rise; but, because of gas exchange, it would devastate the living organisms in the ocean. The vast amount of dissolved CO₂ would increase the amount of hydrogen carbonate ions, which in the overall process, would increase the acidity of the ocean (pH level) and retard the growth of corals because of the secondary buffer produced by the hydrogen carbonate ions – therefore diminishing the number of calcite ions, which are needed to combine with calcium carbonate ions that are needed to make exoskeletons. As for the living corals, they may die out too because of all the stress they would be receiving from the fluctuated environment (coral bleaching).

3. There are only a few reefs off the northeast coast of Brazil, even though it lies in the tropics. How would you explain this?

The reason why there are no coral reefs by the northeast coast of Brazil is because the Amazon River empties out there. The Amazon River carries silt which contributes to a murky appearance. Because of that, coral reefs could not be supported since sunlight wouldn't be able to reach the bottom.