Geography - Coral reefs case study

What are the biotic characteristics of coral reefs?

Coral polyps build coral skeletons

Zooxanthelae live inside coral and have symbiotic relationships with them.

High biodiversity and complex food webs

Fish predate on smaller organisms and coral

What are the abiotic characteristics of coral reefs?

Sunlight needed for photosynthesis - reefs are typically in shallow water with depth from 0-50m

Warm water, between 23-29 degrees C

Clear water, for photosynthesis

Medium to high salinity (32 to 42 ppt)

Where do coral reefs typically form?

Tropical and subtropical oceans between 30 degrees north and 30 degrees south of the equator.

How can industrialisation threaten coral reefs?

• Chemical run off can poison coral polyps or cause other health issues.

• When seawater is used for cooling, local water temperature is increased which can lead to coral bleaching - this is thermal pollution.

• Dredging - the seabed is often dug up to make space for ports, destroying habitats and stirring up lots of sediment

• Enhanced greenhouse effect causes global warming causing coral bleaching.

How can agricultural practices threaten coral reefs?

• Eutrophication - Farmers use fertilisers containing nitrates and phosphates, which can run off into rivers and then the ocean when it rains. This causes algal blooms which block light, preventing photosynthesis.

• Pesticides and herbicides are often poisonous to marine life.

• Deforestation can make land more vulnerable to erosion. The land then is eroded into the reef where sediment prevents photosynthesis.

How can tourism threaten coral reefs?

• Physical damage - Divers or snorkelers often accidentally hit corals with their flippers, causing it to break off. Boats can do the same.

• Pollution - Chemical sunscreens, sewage and waste, can poison coral or cause algal blooms.

• Coastal development - if an area is popular for tourists, development is encouraged. The sea floor might be dredged or mangroves/ forestry might be cleared for hotels.

How can deforestation threaten coral reefs?

• No natural sea defences when forests like mangroves are cleared, sediment erodes faster than before, causes sedimentation, soil settles on the reef and blocks photosynthesis.

• No nutrient filtration - mangroves act as a filter for nutrients and take up lots of them. Without them, reef water can become nutrient rich causing algal blooms.

• Contributes to enhanced greenhouse effect and global warming.