- Coral reefs are underwater structures made by calcium carbonate secreted by corals.
- Coral reefs are colonies of tiny living animals.
- That contain few nutrients.
- Most coral reefs are built from stony corals.
- stony corals turn consist of polyps that cluster in groups.
- Coral reefs called as “rainforests of the sea”.
|A fringing reef can take ten thousand years to form, and an atoll can take up to 30 million years.|
- The polyps are like tiny sea anemones.
- Reefs grow best in;
- They occupy less than 0.1% of the world's ocean surface.
- They provide a home for 25% of all marine species;
|This map shows areas of upwelling in red. Coral reefs are not found in coastal areas where colder and nutrient-rich upwellings occur.|
- Coral reefs are under threat from;
- Overuse of reef resources harmful land-use practices;
-Urban and agricultural runoff
The three principal reef types :
1.Fringing reef – Directly attached to a shore
Borders it with an intervening shallow channel or lagoon.
2.Barrier reef – Separated from a mainland or island shore by a deep channel or lagoon.
3.Atoll reef – More or less circular or continuous barrier reef.
Extends all the way around a lagoon without a central island.
Other reef types;
- Patch reef – isolated
usually within a lagoon/ embayment
circular & surrounded by sand /seagrass.
Patch reefs are common.
- Apron reef – a short reef
extending out & downward from a point or peninsular shore.
- Bank reef – a linear /semicircular shaped
- Ribbon reef – a long, narrow
associated with an atoll lagoon
- Table reef – an isolated reef
without a lagoon
- Habili – in the Red Sea
- Microatoll – certain species of corals form communitie
growth offer a low-resolution record of patterns of sea level change
fossilized microatolls can be dated using radioactive carbon dating
- Cays –small
sandy islands formed on the surface of coral reefs
material eroded from the reef piles up on parts of the reef or lagoon
plants can stabilize cays enough to become habitable by humans
in tropical environments throughout the Pacific, Atlantic and Indian Oceans
- shallowest part of the reef
-subject to the surge & rise & fall of tides.
- The off-reef floor= shallow sea floor surrounding a reef
around tropical islands
atolls drop abruptly to great depths
do not have a floor
- The reef drop-off= for its first 50 m
applies mainly to the reefs surrounding oceanic islands and atolls.
- The reef face= above the reef floor or the reef drop-off
growths of coral and calcareous algae
provide cracks & crevices for protection
provide an ample source of food
- The reef flat= sandy-bottomed flat
containing chunks of coral
reef flat protective area bordering a lagoon
rocky area between the reef & shore
number of fish species living in the area
- The reef lagoon= many coral reefs completely enclose
contains small patches of reef
|Anatomy of a coral polyp|
- Coral heads consist of accumulations of individual animals called polyps.
- Arranged in diverse shapes.
- Polyps are usually tiny.
- They can range in size from a pinhead to 12 inches (30 cm) across.
- Coral polyps do not photosynthesize.
- Have a symbiotic relationship with zooxanthellae.
- These organisms live within the tissues of polyps and provide organic nutrients that nourish the polyp.
- Coral reefs grow much faster in clear water, sunlight.
|thousands of polyps on a single coral branch.|
- An individual polyp uses both reproductive modes within its lifetime.
- Corals reproduce sexually by either internal or external fertilization.
- Internally fertilized eggs develop in the polyp for a period ranging from days to weeks.
|Organisms can cover every square inch of a coral reef|
|Spiral wire coral|
|Tube sponges attracting cardinal fishes, glassfishes and wrasses|