Coral reefs

Question 1

What is a coral reef?

Answer 1

A limestone structure created over a long period of time by coral polyps

Question 2

What are coral polyps?

Answer 2

Tiny animals which often live in the limestone they produce.
They belong to the Cnidarian family like sea anemone and jellyfish
Successive generations of Polyps deposit limestone on limestone, adding to the reef

Question 3

Main features of a coral reef

Answer 3

Coral nutrition

Abiotic factors

Question 4

Coral nutrition

Answer 4

Polyps feed in 3 ways
Cilia trap planktonic organisms
Stinging cells stab and kill the planktonic organisms
90% of sugars come from symbiotic algae

Question 5

Abiotic factors

Answer 5

Warm, stable temperatures between 25 and 29 degrees celcius
High light intensity for photosynthesis
Low turbidity
Constant salinity 
A hard substrate for polyp attachment

Question 6

Importance of coral reefs

Answer 6

Medicines
Fisheries
Protection from erosion
Climate control
Tourism

Question 7

Medicines

Answer 7

Many species produce biologically active substances which can be used in medicines

Question 8

Fisheries

Answer 8

Coral reefs attract a wide variety of wildlife=
An importance source of food or income for local people
Eg. Lobsters can be eaten or exported

Question 9

Protection from erosion

Answer 9

Reefs absorb wave energy

Without the reef, low lying coastal islands are more likely to suffer erosion, floods, storms

Question 10

Climate control

Answer 10

Some of the CO2 from photosynthesis is converted to limestone.
The limestone acts as a carbon sink, protecting against climate change

Question 11

Tourism

Answer 11

Reefs and associated islands attract many visitors, making a major contribution to the economy

Question 12

Threats to coral reefs

Answer 12

Physical damage
Souvenirs and ornaments
Sediments
Climate change
Pollution
Fishing
Disease and predation

Question 13

Physical damage

Answer 13

Living polyps are very sensitive to physical damage
Major causes of damage are swimmers and divers, boat anchors, and litter.
The polyps can regrow but the rate of damage can be higher than the rate of regrowth

Question 14

Souvenirs and ornaments

Answer 14

Trade in 2000 different species is restricted by CITES appendix || but is not always enforced effectively

Question 15

Sediments

Answer 15

Soils and sediments carried by rivers from farms, land reclamation projects, development projects can create turbid water.
Turbid water can settle on the sensitive polyps, killing them.
Turbidity can also block light, preventing photosynthesis
Loss of mangrove forests is contributing to turbid water in coral reefs

Question 16

Climate change

Answer 16

Coral polyps have a narrow range of tolerance
Too high temperatures can make the polyps eject the algae, leading to bleaching
Bleached reefs struggle to support food chains and recover from damage slowly.
Increasing frequent hurricanes increase damage
Rising sea levels could reduce the high light intensity
Increasing CO2 levels can cause acidification, dissolving the reef

Question 17

Pollution

Answer 17

Many pollutants such as oil, pesticides and illegally used cyanide can kill the polyps
Fertiliser leachate can lead to algal blooms which block the light, increasing disease

Question 18

Fishing

Answer 18

Fishermen release harmful pollutants
Overexploitation can cause the food chain to collapse
Trawler nets can cause physical damage
Dynamite fishing stuns the fish but destroys the reef
Cyanide fishing poisons the polyps as well as the fish

Question 19

Disease and predation

Answer 19

Algae on the surface can provide food to bacteria hat kill the polyps
Overfishing of parrotfish and fertiliser runoff cause the algae to become more common

Question 20

Case study- Crown of thorns starfish

Answer 20

The crown of thorns is a very large starfish which secretes enzymes that digest coral polyps
The rate of regrowth is usually higher than the rate of damage
Human actions has allowed the rate of damage to exceed the rate of regrowth
The giant triton is a mollusc that eats the crown of thorns starfish but its numbers have been reduced due to collection for souvenirs
The humphead wrasse is a starfish predator but has been overfished
Fertiliser runoff increased algal growth which feeds the starfish larvae while the algae reduce the amount of larvae which are eaten by the polyps

Question 21

Conservation of coral reefs

Answer 21

Designated sites
Fixed mooring buoys so anchors are unneeded
Educated/trained swimmers/snorkellers/divers
No take zoning
Sustainable development
Controlled developments
Controlled activities on land to reduce runoff
Environmental protection for other sites eg. Mangrove forests