IGCSE Geography Lesson: Coastal Ecosystems

Lesson Outcomes

By the end of this lesson you should know:

  • The distribution and features of the following coastal ecosystems
    • Coral reefs
    • Mangroves
    • Salt marsh
    • Sand dunes

Coastal Ecosystems

An ecosystem is a community of living organisms, both plants and animals, that share an environment.

Coral Reefs

Coral reefs are typically found in the tropics, between 20º north and south of the equator. Based upon geographic distribution, 60% of the world's reefs are found in the Indian Ocean and Red Sea, 25% are located in the Pacific Ocean, and 15% in the Caribbean Sea.

Coral reefs require certain conditions to form:

  • Water temperatures of 18ºC or above
  • Corals require a lot of sunlight so clear waters are essential for growth
  • This means that coral reefs are unlikely to be found in sediment rich waters e.g. near a river mouth
  • accompanying plankton and seaweed would block out the light
  • Due to their need for light, corals are not found in seas deeper than 25m.

Healthy coral reefs can support a great diversity of life, for example the Great Barrier Reef found off the coast of Australia.

360° Video 10 mins

360° Coral reef virtual tour:

Video 10 mins

Biodiversity on coral reefs:


Mangroves are trees and shrubs that grow in saline (brackish) coastal habitats in the tropics and subtropics. They are found in intertidal zones along estuaries and marine shorelines.

Mangroves have adapted to survive in the following conditions:

  • They are regularly flooded by seawater
  • At low tide there may be freshwater flooding
  • They can survive high temperatures and choking sedimentation.

The roots of mangrove trees trap mud and create new land which provides a new habitat for other plant species, as this happens the mangroves colonise new areas in the intertidal zone.

Video 5 mins

Pygmy sloths in the mangrove:

Salt Marsh

Salt marshes are intertidal areas of fine sediment transported by water and stabilised by vegetation. Once vegetation has established the rate of sedimentation, accretion often increases. In addition, organic matter is added to the marsh surface. This occurs due to the accumulation of litter on the sediment surface and root growth below the surface.

There are four elements necessary for the initial development and growth of a salt marsh:

  • A relatively stable area of sediment covered by the tide for a short time.
  • A supply of suitable sediment available.
  • Low water velocities for some of the sediment to be deposited.
  • A supply of seeds for the establishment of vegetation cover.

Sand Dunes

Sand dunes are small ridges or hills of sand found at the top of a beach, above the usual maximum reach of the waves. They form from wind blown sand that is initially deposited against an obstruction such as a bush, driftwood or rock. As more sand particles are deposited the dunes grow in size, forming rows at right angles to the prevailing wind direction. If vegetation, such as Marram Grass and Sand Couch, begins to grow on the dune its roots will help to bind the sand together and stabilise the dunes.

Activity 4 10 mins

Describe how sand dunes change as you move from the strandline inland.

End of Lesson Check

Do you know…

  • The distribution and features of the following coastal ecosystems
    • Coral reefs
    • Mangroves
    • Salt marsh
    • Sand dunes?

Last modified: Thursday, 28 July 2022, 10:41 AM