Chapter 1. Identity card of a coral reef
Global distribution of coral reefs - What do corals need?
Bora Bora seen by IKONOS (Tahiti).
Source: © 2006 GeoEye.
Objectives
Students learn to read and interpret the distribution of physical phenomena on a global map.
Students learn how to work with a basic GIS programme.
Materials
- Download the worksheet Global distribution of coral reefs - What do corals need? (5 MB .rtf file)
- Internet access
Time needed
One class period
Procedure
- This worksheet can serve as a replacement of some theoretical pages in chapter 1 'Identity of a coral reef'. Both pages 'Global distribution of coral reefs' and 'What do corals need?' are processed in this exercise.
- This exercise can be given as homework or used as an exercise in class.
Answers
To localize the areas where corals occur, open the following site: https://catalogue.odis.org/view/612
Go to 'Maps - Location of coral reefs'. Switch on the layer 'Reef Basemap'.
- Look for the latitudes in your atlas. Between which latitudes can the majority of the corals be found?
Between 20° North Latitude and 20° South Latitude.
- Name four important regions where corals are located.
- Gulf of Mexico-Carribean Sea
- Red Sea
- Indo-Pacific, Islands of Oceania
- The Persian Gulf
Because of the high temperature of the sea.
- Can you explain why coral reefs are rare or absent in the tropical Atlantic of the west-coast of South America and west-coast of Africa?
TIP: Study the map of all oceans currents on earth in your atlas and make a link with previous question.
Mainly due to the upwelling of cold water currents from the deep parts of the ocean.
- Look up in your atlas where the Amazon and the Congo River systems flow into the ocean. Are there a lot of corals in this region?
No
If you think of the difference between ocean water and river water, what can you conclude concerning the appearance of corals?
A lot of fresh water from the rivers flows here into the ocean. Thus, we can conclude that corals need a certain degree of salinity to survive.
Extra: there is another explanation for the absence of corals close to large river mouths. Can you think of one?
Corals need clear water. Water transparency can be highly influenced by runoff bringing suspended sediments into coastal waters.
- Knowing that corals live in symbiosis with algae,
can you explain why most of the corals are localized in shallow areas?
Algae need light for photosynthesis and light is attenuated with depth.
- Because polyps are sessile, oxygen and food have to be brought to the polyps in one way or another.
On the other hand, the coral larvae have to be distributed. How do they cope with this problem?
Ocean waves and currents bring oxygen to the polyps and distribute the coral larvae.
CONCLUSION: After answering the previous questions, can you sum up the limiting physical factors for the occurrence of corals?
