Coastal Ecostystems

• Coral Reefs


  • Temperature: Corals cannot tolerate water temperatures below 18°C but grow best at 23°C – 29°C. Some can stand temperatures as high as 40° C for short periods. This is why coral reefs normally grow between the Tropic of Capricorn and the Tropic of Cancer
  • Light: Corals need light for photosynthesis due to the algae, called zooxanthellae, that live in their tissue
  • Water: Corals are generally found at depths of less than 25m where sunlight can penetrate. The water must also be clear and clean to allow for optimum photosynthesis to occur
  • Salinity: Since corals are marine animals they need salty water to survive, ranging from 32-42% saltwater
• Coral Reefs


  • Wave action: Corals need well-oxygenated, clean water and wave action provides this
  • Exposure to air: Although corals need oxygenated water, they cannot be exposed to air for too long or they will die
  • Sediment: All corals need clear, clean water. Any sediment in the water will block normal feeding patterns by reducing the availability of light affecting the photosynthesis of the microscopic algae 'zooxanthellae' living in polyp tissue
• Types of Coral Reefs

  • Fringing Reefs: Reefs that form around a land mass
  • Barrier Reefs: Found parallel to the shore but are separated by a channel of water. The Great Barrier Reef in the Coral Sea, off the coast of Queensland, Australia is a good example
  • Atolls: Horseshoe-shaped rings, consisting of a coral rim that encircles a lagoon
• Mangroves


  • They sit in water between 0.5 to 2.5 metres high
  • They range in size from small shrubs to trees over 60m high
  • They have numerous tangled roots that grow above ground and form dense thickets
  • They need high levels of humidity (75 - 80%) and rainfall per annum (1500 - 3000 mm)
  • The ideal temperature is around 27° C but are adapting to more temperate climates
• Mangrove Root Systems


  • Prop Roots: Mangrove root system is complex, with a filtration system to keep salt out
  • Snorkel Roots: Some have snorkel-like roots that stick out of the mud to help them take in air
  • Others use 'prop' roots or 'buttresses' to keep their trunks upright in the soft sediment at the tidal edge
• Sand Dunes


  • They are the accumulation of sand, shaped into mounds and ridges by the wind
  • Found at the back of a beach, above the maximum reach of the tide
  • Sand dunes can be small ridges or large hills usually found at the back of a beach
  • They can extend backwards for many miles as well as along the beach
  • They are an important ecosystem supporting unique flora and fauna that have adapted to live within the dune system
• Formation of a Sand Dune

  1. Wind-blown sand is deposited against an obstruction - pebble or driftwood

  2. As more sand particles are caught, the dunes grow in size, forming rows at right angles to the prevailing wind

  3. Over time, the ridges of the dunes will be colonized and fixed by vegetation in a process called succession
• Coastal Sand Dune Succession

  • Embryo Dunes
  • Fore Dunes
  • Yellow Dunes
  • Grey Dunes
  • Mature Dunes
• Salt Marshes


  • They are typically very flat, with numerous channels running through them
  • They form in coastal areas that are well sheltered, such as inlets and estuaries where fine sediments can be deposited
  • They form in brackish water
  • They begin as tidal mud flats, gaining height as more sediment is deposited
  • This builds up to and above the level, and frequency of tidal flooding ensuring that the soil never dries out and remains muddy and sticky
• Salt Marsh Succession


  1. Pioneer species of halophyte plants begin to colonise

  2. As these plants die and add nutrients to the soil, sediment builds up. This makes the conditions more favourable and other species start to develop

  3. The process of the development of vegetation, over time is known as succession. In a salt marsh, this is known as a halosere
• Succession

  The process of the development of vegetation over time
• Halosere

  The process of succession in a salt marsh
• Lower marshes

  • Flooded daily by the rising tide
  • Good coastal defences, acting as a natural buffer against coastal erosion and flooding
• In many areas, salt marshes have been reclaimed for agriculture or development, and are threatened by human activities
• Explain one physical factor that influences the distribution of mangrove ecosystems

  1. Identify a way (temperature, light, water depth, salinity, wind direction, level of shelter)

  2. Develop and further explain the factor
• Coastal mangroves

  • Need a high temperature of around 27°C otherwise they will not grow, although some mangroves have adapted to more temperate conditions such as New Zealand
  • Need shallow water between 0.5 to 2.5 metres in depth, but can survive where the tidal ranges go slightly above or below this level
  • Need high levels of humidity between 75 and 80% to enable them to grow
  • Need a high level of rainfall between 1500 and 3000 mm per annum, this can be gained from rainfall or moisture in the air making tropical climates ideal