Characteristics of Coastal Ecosystem (Edexcel IGCSE Geography)

Characteristics of Coral Reef Ecosystems

Spec point — 4GE1-S3.043

• An ecosystem is a community of interacting biotic organisms and abiotic factors

• All ecosystems, whether on land or in water function in the same way

• All survive by nutrient cycling around three stores

  • Biomass
  • Litter
  • Sea Water

*Nutrient cycle of a coastal ecosystem *

Nutrient cycle of coastal ecosystems

Mangroves

• Nutrient store– mud/sand
• Biomass store– plants and animals
• Litter– dead plants and animals
• Degrades in water
• Transfers– water

Sand dunes

• Nutrient store– mud/sand
• Biomass store– plants and animals
• Litter– dead plants and animals
• Degrades in water
• Transfers– land

Salt Marsh

• Nutrient store– mud/sand
• Biomass store– plants and animals
• Litter– dead plants and animals
• Degrades in water
• Transfers– land

Coral

• Nutrient store– sea water, rivers entering the sea, on-shore currents
• Biomass store– coral polyps, seaweed, fish, crustaceans and invertebrates
• Litter– dead coral polyps, seaweed, fish, crustaceans and invertebrates
• Degrades in seawater
• Transfers– tidal and ocean currents

Exam Hint Please ensure you have a clear understanding of nutrient cycling in these ecosystems, especially the distinction between abiotic and biotic factors. Examiners might ask you to name one or both of these factors from a list.

Biotic components of a coral reef

• A coral reef is a well-organised food web comprised of:

  • producers
  • consumers
  • scavengers
  • decomposers

Producers

• Producers in a coral reef include seaweed, seagrass, and phytoplankton. zooxanthellae are also producers that provide the nutrients from photosynthesis to coral

Consumers

• Consumers are organisms that eat other organisms to gain energy.

  • There are three main types of consumers in a food web: primary, secondary, and tertiary

    • Primary consumers only eat producers – the green sea turtles graze on seagrass
    • Secondary consumers eat primary consumers – stingrays, octopuses, squid, and larger fish, for example
    • Tertiary consumers, also called apex predators, are carnivores that do not prey upon themselves. These consumers help maintain the balance of the ecosystem - sharks, dolphins, tuna, barracuda, etc.

Scavengers

• Scavengers feed on dead and decaying plants and animals – crabs and lobsters scavenge for food

Decomposers

• Decomposers bring nutrients back into the ecosystem to support another cycle – examples include bacteria, sea cucumbers, and fungi

Abiotic features of a coral reef

• Corals need a certain amount of sunlight to survive

  • Too little light and the zooxanthellae will not be able to photosynthesise and produce food for corals
  • Too much light may cause corals to expel zooxanthellae, causing bleaching

• Depth: As corals need light, they are typically found at approximately 25 meters

• Water temperature: Corals thrive in the warm waters of the tropics. They prefer a temperature range of 23-25°C but will survive at lower and higher temperatures for short periods

• Salinity: Corals need salty water

• Air: Can survive out of water for very short periods

• Water: Corals need clean, clear water

Characteristics of Mangrove Ecosystems

Spec point — 4GE1-S3.043

Biotic components of a mangrove

Producers

• Mangroves are the producers of their own ecosystem

  • Many organisms feed on the detritus created from falling leaves
  • Phytoplankton can float on the surface of the water and algae grow on the mangroves' roots

Consumers

• Primary consumers are usually the decomposers (e.g. the mangrove tree crab). Small fish, crabs, clams, and shrimp feed off of the detritus. Very few consumers directly feed on the mangroves
• Secondary consumers are the larger predatory fish, turtles, and crabs
• Tertiary consumers include birds (e.g. herons and ospreys), eels, saltwater crocodiles, tigers, and humans

Scavengers

• Scavengers include shrimp, crabs mussels and mullet

Decomposers

• Decomposers include worms, bacteria and fungi

Abiotic features of mangroves

• Temperature: Mangroves typically grow in areas where the temperature does not drop below 19°C
• Oxygen: Just like other plants, mangroves need oxygen to survive. Complex root systems allow the mangroves to receive the oxygen they need by sticking out of the water
• Salinity: Mangroves have adapted to live in salt water, with some removing excess salt through their leaves
• Soil: Mangroves can grow within the intertidal zone of a coast. The soils are made up of sand, silt, and mud
• Wave energy: Mangrove vegetation cannot develop on exposed coasts with a lot of wave energy or currents that move sediments, which would stop seeds from colonising
• Ocean currents: These distribute mangrove seeds and help keep the areas full of trees

Characteristics of Sand Dune Ecosystems

Spec point — 4GE1-S3.043

Biotic components of sand dunes

Producers

• Producers that provide the initial beach fuel for dunes include:

  • phytoplankton, microscopic algae (green scum found on a beach), detached seaweeds (such as kelp and seagrass), and blown-in seeds.
  • These support the growth of pioneer species such as couch grass and lyme grass. As succession continues, multiple species of vegetation begin to colonise – marram grass, gorse, sea buckthorn, heathers, red fescue, etc.

Consumers

• Primary consumers: beetles, butterflies, moths, bees, wasps, flies, rabbits, etc.
• Secondary consumers: sand lizards, snakes, spiders, frogs, bats, etc.
• Tertiary consumers: seagulls, waders, hawks, swans, bats, etc.

Scavengers

• Scavengers: crabs, beetles, flies, wasps, crows, rats, etc.

Decomposers

• Decomposers: flies, fungi, bacteria, weevils, etc.

Abiotic features of sand dunes

• Wind – an onshore prevailing wind is needed to blow the dried sand into ridges
• Tidal range – needs to be large to allow sand to dry
• Water – a mix of fresh and saline to support pioneer species
• Sand – large quantities needed
• Beach – needs to be wide
• Obstacles – needed for sand to accumulate behind

Characteristics of Salt Marsh Ecosystems

Spec point — 4GE1-S3.043

Biotic components of salt marshes

Producers

• Producers – algae, seaweed, rushes, samphire, cord grass, salt marsh hay etc.

Consumers

• Primary consumers – fish, insects, mussels, crabs, bees, oysters, shrimp, etc.
• Secondary consumers – fish, mice, frogs, herons, lizards, sandpipers, bats, etc.
• Tertiary consumers – harriers, sea eagles, gulls, etc.

Scavengers

• Scavengers – snails, rats, crows, flies, crabs, etc.

Decomposers

• Decomposers – fungi, bacteria, worms, etc.

Abiotic features of salt marshes

• Waves – sheltered away from the open sea & destructive waves, usually behind a spit or in sheltered bays
• Water – brackish (mix of fresh and salty)
• Tidal Range- this is large with occasional flooding. Mudflats need to be exposed to colonise
• Mud – sediment needed to build up mud flats
• Elevation – needs variation in height to build up mud flats and stabilise marshes

Worked Example Explain two factors affecting the distribution of coral reef ecosystems.

(4 Marks)

• Answer:

• You need to state 2 reasons why coral reefs grow where they do or why they might stop growing there

  • Need temps of 23-28 degrees **(1)**so only found in the tropics (1)
  • Light is needed for coral to grow (1), as they only grow in areas of shallow water where the light can penetrate (1)
  • Global warming (1) leading to sea-level rise (1)
  • Human impact (1)for example climate change causing the temperature of water to change/coral bleaching (1)
  • Pollution from tourist activity** (1)** damages coral (1)
  • Any other appropriate response