Coastal and Oceanic Landform (18. Coral Reef)

                                                                                                            Back to coastal and Oceanic Landform

• 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;

                             -Warm

                             -Shallow

                             -Clear

                             -Sunny

                            -Agitated waters

• They occupy less than 0.1% of the world's ocean surface.

• They provide a home for 25% of all marine species;

                       -Fish

                      -Mollusks

                      -Worms

                     -Crustaceans

                     -Echinoderms

                    -Sponges

                    -Tunicates

                    -Cnidarians

This map shows areas of upwelling in red. Coral reefs are not found in coastal areas where colder and nutrient-rich upwellings occur.

Biodiversity of a coral reef

• Coral reefs flourish provide few nutrients.

• Coral reefs are under threat from;

                     -Climate change

                    -Ocean acidification

                   -Blast fishing

                  -Cyanide fishing

• Overuse of reef resources  harmful  land-use practices;

                  -Urban and agricultural runoff

                  -Water pollution

The three major zones of a coral reef

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

                                     comparatively small reef outcrop

                                     usually within a lagoon/ embayment

                                    circular & surrounded by sand /seagrass.

                                    Patch reefs are common.

• Apron reef – a short reef

                                      resembling a fringing reef

                                      more sloped

                                      extending out & downward from a point or peninsular shore.

• Bank reef – a linear /semicircular shaped

                                    larger than a patch reef

• Ribbon reef – a long, narrow

                                         possibly winding reef

                                         associated with an atoll lagoon

• Table reef – an isolated reef

                                     approaching an atoll type

                                     without a lagoon

• Habili – in the Red Sea

• Microatoll – certain species of corals form communitie

                                      the vertical growth limited by tidal height.

                                      growth  offer a low-resolution record of patterns of sea level change

                                     fossilized microatolls can be dated using radioactive carbon dating

• Cays –small

                      low-elevation

                      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

The reef surface 

 - shallowest part of the reef

 -subject to the surge &  rise &  fall of tides.

• The off-reef floor= shallow sea floor surrounding a reef

                                                        occurs by reefs on continental shelves

                                                        around tropical islands 

                                                        atolls drop abruptly to great depths

                                                       do not have a floor

                                                       usually sandy

                                                       supports seagrass

• The reef drop-off=  for its first 50 m

                                                        habitat for many reef fish

                                                        applies mainly to the reefs surrounding oceanic islands and atolls.

• The reef face=   above the reef floor or the reef drop-off

                                               usually the richest habitat

                                               growths of coral and calcareous algae

                                               provide cracks &  crevices for protection

                                               provide an ample source of food

• The reef flat= sandy-bottomed flat

                                          behind the main reef

                                          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

                                                  creating a quiet-water lagoon

                                                  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.

Brain coral

Pillar coral

• Coral specie

                                 -wrinkled brains

                                 -cabbages

                                -table tops

                                -antlers

                                -wire strands

                               -pillars

• 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

Staghorn coral

Table corel

Tube sponges attracting cardinal fishes, glassfishes and wrasses