Coral Reefs

Coral Reefs are large offshore ridges primarily composed of limestone (calcium carbonate) by living organisms called coral polyps. Coral polyps are tiny invertebrates that secrete calcium carbonate which form the base for the coral colony.

Zooxanthellae & Coral Colour

Zooxanthellae is a type of algae that has a symbiotic relationship with coral. The algae carry out photosynthesis and live inside the tissues of coral polyps so the food produced from photosynthesis is shared with the corals. The zooxanthellae is responsible for bright colours as the coral tissue itself is white. This is an example of mutualism.

Types of Coral Reefs

1. Fringe Reefs

2. Barrier Reefs

3. Atoll Reef (Not required to learn for CSEC)

   1. Fringe Reef - A fringe reef grows either from the shore or near the shore, sometimes with a shallow lagoon. Fringe Reefs go parallel to coasts in shallow waters. For example, The Buccoo Reef, a fringe reef located in Tobago, Trinidad and Tobago.
   2. Barrier Reef - A barrier reef develops in shallow low lying coastal areas. When coastal plains are flooded the corals begin to grow at a distance off the coastline. Sometimes there are wide lagoons or shallow seas  between the Barrier Reef and the shore. For example, The Belize Barrier Reef located in Belize, the second largest in the world.

Conditions Necessary For Coral Reef Growth

• Salinity Level - Coral reefs can only grow in waters with the right salt levels which is why in areas with river mouths coral reefs were not seen as fresh water mixes in.
• Warm Temperature - Coral reefs needs to be in warm seas to grow hence why most reefs are located between the Tropic of Cancer (23.4°N) and the Tropic of Capricorn (23.4°S). Optimal temperatures for coral reef growth are around 23°C to 25°C.
• Shallow Depth - Corals have to be in shallow waters in order to have enough sunlight penetrating as the algae in the coral polyps need them to carry out photosynthesis.
• Clean Water - Water containing silt and sediment can lessen the amount of sunlight penetration hence the water needs to be clean. Also pollutants such as sewage and chemicals can damage corals.

Importance of Coral Reefs

• Tourism - In the Caribbean coral reefs are often exploited by the tourism industry and many activities are associated with corals such as scuba diving and boat tours which helps to contribute to local GDP.
• Ecological Diversity - Coral reefs often contain thousands of fish species while providing food and shelter for the species. The reef is also used as a breeding ground which sustains the continuation of the species
• Natural Barrier - Corals especially in a barrier reef slow down the energy of waves approaching the shore protecting it during storms and tsunamis. Also sometimes dead corals and sediment pile up to form islands.
• Beach Formation - The breakdown of corals by erosion provides building material for some of the white sandy beaches seen in tropical areas like the Caribbean.

Threats To Coral Reefs

• Coral Bleaching - Due to sea level rise, less light is reaching the algae within the coral polyps and they cannot photosynthesis to provide food so the corals expel the algae and lose their colour leaving behind white dead corals.
• Pollution - The dumping of chemicals and fertilizers in waterways that eventually reach the sea hinder the growth of corals and may sometimes lead to death. They may also promote the growth of other organisms leading to competition for resources like oxygen.
• Global Warming - As stated earlier, coral reefs require an optimal warm temperature of around  23°C to 25°C. Rising temperatures pose a threat to coral reefs as additional heat may be damaging or deadly to the reefs.

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