Coral reefs Flashcards
(30 cards)
What is coral?
A living organism (polyp) found in clear, tropical waters. Corals live in communities known as reefs. They secrete lime and build a skeleton
What is zooxanthellae?
Algae that live in a symbiotic relationship with coral and give it its colour
Why are coral reefs important to society?
- Seafood
- Commercial products
- Tourism
- Medical products
- Coastal protection - protect from storm waves
How much do coral reefs currently contribute to the global economy?
$100bn
How is coral reefs formed?
Corals are tiny marine animals called polyps that form reefs when millions of them live together in colonies.
Free swimming coral polyp larvae attaches to a rock on the bed.
The coral polyp works with (symbiotic relationship) with zooxanthellae (an algae).
The coral provides the protective environment and the algae carries out photosynthesis within the polyp tissues of the coral, providing it with glucose, glycerol and amino acids
The coral polyp uses the products of photosynthesis to grow and secrete calcium carbonate.
A limestone cup is created around the organism.
The polyp then develops many clones and connect, forming a colony, acting as a single organism.
The colonies join and form a reef.
What are the factors affecting coral growth?
- Temperature
- Light
- Wave action
- Salinity
- Exposure to air
- Sediment
- Sea bed
Why is temperature a factor for coral growth?
Sea temperatures have to be above 18C and they grow best where sea surface temperatures average between 22C and 25C. This means they are only found within 30 degrees of the equator
Why is light a factor for coral growth?
Corals cannot grow in water deeper than 30m because of their symbiotic relationship with the single-celled algae which need light to photosynthesise. Corals feed on plankton which needs sunlight
Why is wave action a factor affecting coral growth?
Outer edge of the reef grows highest because that is where oxygen and food supplies are most abundant
Why is salinity a factor affecting coral growth?
Corals grow best where salt levels are high
Why is exposure to air a factor affecting coral growth?
The coral polyps can’t survive for long above the water, so most of the reef is at low or below low tide level
Why is sediment a factor affecting coral growth?
Polyps need clean, clear, sunlight water so they can’t live where rivers bring muddy sediments into the sea
Why is the sea bed a factor affecting coral growth?
There has to be solid surface on which the reef can grow. This is why they are coastal features, forming in shallow offshore waters
Why are corals at risk?
Enhanced global warning
Pollution
Physical damage
Why is enhanced global warming a risk to corals?
Increased acidity
Sea level rise
1-2C rise in temperature
Why is pollution a risk to corals?
Chemicals from land
Sewage
Oil
What can cause physical damage to corals?
Quarrying
Dumping of sediment
Tourism
Nets/blasting
Natural hazards
Why do corals bleach?
If high water temperatures persist for a week or more the polyps reject their plant partners and the coral appears bleached. If the heat persists for too long the coral will die
What happens to dead coral?
Algae grows on dead coral making it impossible for new colonies to form. If there are enough fish in the reef they can clean the algae away and allow corals to return
How do volcanic islands form?
An island is formed by a volcanic cone which becomes extinct. Usually due to plate tectonics.
How do fringe reefs form?
As the island and ocean floor subside, coral growth builds a fringing reef, often including a shallow lagoon between the land and the main reef
How do barrier reefs form?
As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper lagoon inside
How do atolls form?
Ultimately, the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon
What are the 4 typical zones on a coral reef?
Lagoon or flat reef
Reef crest
Fore reef
Reef slope
