Coral Reefs

What phylum and class are corals found in?

Phylum Cnidaria. Class Anthozoa, a few are Hydrozoa.

What are the parts of coral?

The soft body of a coral is called a polyp, and it sits in a corallite skeleton, made of calcium carbonate.

What does hermatypic and ahermatypic mean?

Hermatypic: Reef building corals, also known as Stony corals.
Ahermatypic: Corals that do not build reefs.

What are zooxanthellae and why are they considered mutualistic?  

Type of dinoflagellate that lives in the tentacles of coral. Consumes coral waste and produces food for coral in exchange for food and home.

What is a censosarc?

Thin layer of tissue that connects the coral polyps.

What type of larvae do corals possess?

Planula larvae.

How can coral get their nutrition?  With what structures can they prey on other organisms?

Zooxanthellae supply nutrition. Polyps also catch prey with zooplankton and detritus with tentacles with nematocysts. Mesenterial filaments, secrete digestive enzymes. Mucus nets.

What other organisms can contribute to reef structure besides the stony corals? 

Coralline algae (calcium carbonate). Soft corals such as sea whips and sea fans, other cnidarians such as hydrozoans or anemones. Sponges and bryozoans.

What conditions are best for reef growth? Where are they usually found?

Hard substrate, close to land. Shallow depths with light, not deeper than 50m. Narrow temperature range. Located within 30 deg latitude of equator in water that averages 20 deg C. Narrow salinity range. Low sediment load in water. Low pollution. Narrow range of pH.

What is coral bleaching and what stressful things can lead to that?

Expelling zooxanthellae. Stress due to conditions not being met. High temperature, poor water quality, increased sediment in water column, wave stress, disease.

How can corals reproduce? What is polyp bailout?

Reproduce asexually and sexually. Hermaphroditic spawners. Polyp bailout is when a polyp leaves and creates it’s own coral by asexually reproducing.

Who suggested that coral reefs go through sequential developmental stages? What are the 3 stages?

Charles Darwin suggested that coral reefs have 3 sequential stages. Fringing reefs, barrier reefs, atolls.

What’s the difference between shelf reefs and oceanic reefs?

Shelf reefs: by continents.
Oceanic reefs: around islands.

What are the reef flat, the reef crest and the reef slope?

Reef flat: reef that may be exposed during low tide.
Reef crest: shallow edge of the slope
Reef slope: highest cover of coral

What characteristics do fringing reefs have?

Simplest, most common form of reefs. Develop near-shore. Inner reef flat, slow growth and outer reef slope, has most amount of coral. Reef crest has the highest growth.

What characteristics do barrier reefs have? What are the parts of the barrier reef? Where is there most coral growth?

Further away from shore than fringing reefs. Have a deep lagoon between shore and reef. Consists of a back-reef slope, a reef flat, and crest and fore-reef slope. Most growth on crest and fore-reef slope. Patch reefs, scattered coral formations.

What are keys (cays)? How do they form?

Waves often wash sediment onto back reef slope or reef flat. Reduced coral growth in this area. Sediment may accrue to form small islands called keys.

What characteristics do atolls have?  What are the parts of the atoll? 

Circular reef structure surrounding a central lagoon. Sand cays may be a part of the atoll. Has a reef flat and inner and outer reef slopes. Lagoon depth is 200 feet or less.

What is the process of a fringing reef becoming an atoll?   

1. Volcanic island forms

2. Coral begins as a fringing reef around island

3. Weathering and geologic activity lowers level of the island (subsidence) forming a barrier reef

4. With further subsidence, the island disappears below the water’s surface, leaving only the outer band of coral.

Are coral reefs productive?  What about tropical waters in general?  Why are reefs so productive if the environment around them is not? 

Coral reefs are very productive, tropical waters are not, lack of nutrients. Reefs are productive due to the zooxanthallaes. Recycled nutrients

What factors are limiting (aka what do organisms mainly compete for) in the coral reef habitat?

Light and space. Coral reef is a packed environment that leads to competition.

What are some strategies that corals use to outcompete other corals and other organisms?

Light and space. Coral reef is a packed environment that leads to competition. Some grow fast and upright to maximize ability to reproduce quickly. Others grow slow but massive to out-compete other organisms in the long run. Coral may feed directly or sting one another when they contact each other.

What does the Crown of Thorns Sea Star prey upon? 

Coral