Edexcel IGCSE Geography 复习笔记 2.2.2 Characteristics of Coastal Ecosystem

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

Overview of Coastal Nutrient Cycling

Biotic Components of a Coral Reef

• A coral reef is a well-organized food web comprising of:
  • Producers
  • Consumers
  • Scavengers
  • Decomposers
• Producers in a coral reef include seaweed, seagrass, and phytoplankton. zooxanthellae are also producers that provide the nutrients from photosynthesis to coral
• 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 sea grass
  • 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 and barracuda, etc.
• Scavengers feed on dead and decaying plants and animals - crabs and lobsters scavenge for food
• Decomposers bring nutrients back into the ecosystem to support another cycle - examples include bacteria, sea cucumbers, and fungi

Abiotic Features of a Coral Reef

• Light: Corals need some sunlight to survive:
  • Too little, then the zooxanthellae will not be able to photosynthesize and produce food for corals.
  • Too much 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 of time
• Salinity: Corals need salty water
• Air: Can survive out of water for very short periods of time
• Water: Corals need clean, clear water

Biotic Components of a Mangrove

• 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
• 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 include shrimp, crabs mussels and mullet
• 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 coast 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 

Biotic Components of Sand Dunes

• 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 colonize - marram grass, gorse, sea buckthorn, heathers, red fescue, etc.
• 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: crabs, beetles, flies, wasps, crows, rats, etc
• Decomposers:  flies, fungi, bacteria, weevils, etc

Abiotic Features of Sand Dunes

• Wind - an onshore prevailing wind is needed to blow 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 spices
• Sand - large quantities needed
• Beach - needs to be wide
• Obstacles - needed for sand to accumulate behind

Biotic Components of Salt Marshes

• Producers - algae, seaweed, rushes, samphire, cord grass, salt marsh hay etc
• 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 - snails, rats, crows, flies, crabs etc
• 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 - large tidal range with occasional flooding. Mud flats 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