Coral Reefs

Question 1

What conditions are required for the growth of coral reefs?

Answer 1

Shallow water (10m)

• Light intensity increases with depth. Polyps need algae which in turn need light for photosynthesis.

Moderate wave activity

• To bring nutrients to algae

Sediment-free

• Sunlight and oxygen needs to get through to algae for photosynthesis. Sediment also provides ammunition for attrition during storms. Sediment thirdly settles on polyps making them unable to feed.

Unpolluted

• Runoff from farms after rain can leave fertilisers and sewage can cause a population explosion of starfish which eat polyps.

Solid surface e.g. shipwreck, rock

• From which polyps can attach themselves and grow outwards.

Sea temperatures 22-25˚C

• Warmth needed for enzymes.

High salinity of water

• Required for correct balance of water-ions.

Question 2

How do coral reefs form?

Answer 2

• Polyps grow on a hard stony structure in the right conditions.
• Polyps form reefs when they live in colonies.
• Skeletons (calcareous) join with other skeletons and form a stony mass.
• As one generation dies, the next generation grows on top of it, which grows the reef upwards and outwards.

Question 3

Why can coral reefs not develop at river mouths?

Answer 3

• Sediment enters the sea at estuaries.
• Influx of freshwater lowers salinity of sea (polyps grow best in salty water).
• Rivers bring pollutants into the sea, especially after heavy rain. Runoff from farms such as sewage and fertilisers cause a population explosion of starfish which feed on coral.
• Sediment can act as ammunition in storms.

Question 4

Why do polyps need clean, sediment-free water?

Answer 4

• In cloudy water (water with sediment in suspension), sunlight cannot permeate through. Sunlight is necessary for the plankton to photosynthesise, which is the main food source of the polyps.
• If sediment settles on polyps, they are unable to feed.
• Sediment can cause abrasion and break up the reef during storms.

Question 5

What is the relationship between polyps and algae?

Answer 5

• Live symbiotically.
• Algae benefit polyps:
  
  • Take away waste products
  • Use waste products and sunlight to make glucose for polyps to feed on
• Polyps benefit algae:
  
  • Safe place to live
  • Waste products of polyps needed for photosynthesis

Question 6

What is a coral reef?

Answer 6

An amalgamation of corals: small, micro-organism called a polyp that has a hard limestone outer skeleton.

Question 7

Where are coral reefs found?

Answer 7

Found between the tropics - between 20 degrees North and South of equator.

Found close to coastline.

Question 8

What are the benefits of coral reefs?

Answer 8

• Tourism - jobs/money
• Barrier against erosion
• Medicines

Question 9

What are the threats to coral reefs?

Answer 9

• Farming leading to eutrophication
• Tourism and boats scraping coral
• Industry pollutes water - sediment
• Global warming - changing temperatures - get bleached
• Fishing disrupts food chain