Coasts 2 Flashcards
What is a fringing reef?
They are low, narrow bands of coral next to the coast. They consist of a platform of coral which is connected to the land and which has grown out from it.
The surface of the coral platform is usually slightly concave and is filled by a shallow lagoon which occupies the space between the land and the outwards edge of the reef.
The lagoon is less than 500m wide.
The seaward edge of the reef is often the highest due to breaking waves oxygenating the water and providing food for the the polyps.
(e.g. Fiji and Mauritius).
How do Atoll reefs form?
Atoll reefs rise from submerged volcanic foundations and often support small wave-borne detritus.
Atoll reefs are essentially indistinguishable in form and species composition from barrier reefs except they are confined to the flanks of submerged oceanic islands. There are over 300 atolls in the Indian and Pacific Oceans but only 10 are found in the western Atlantic.
What was Charles Darwin’s theory about the formation of barrier and atolls?
The growth of barrier reefs and atolls is a gradual process, the main reasons being subsidence. The coral reefs grow upwards from submerging foundations.
A fringing reef grows around an island, for example, as the island slowly subsides, the coral continues to grow, keeping pace with the subsidence.
Coral growth is more vigorous on the outer side of the reef, so a i forms a higher rim, whereas the inner part forms an increasingly wide an deep lagoon.
Eventually, the inner island is submerged, forming a ring of coral that is the atoll.
What was Murray’s theory about the formation of barrier and atolls.
The base of the reef consisted of a submarine ill or plateau rising from the ocean floor. These reached 60m of the sub-surface volcanic peaks or wave-worn stumps. As the fringing reef grows, pounded by breaking waves, masses of coral fragments gradually accumulate on the seaward side, washed by the waves, and are cemented into a solid bank.
What was Daly’s theory about the formation of barrier and atolls?
A rise in sea level may be responsible for the formation of barriers and atolls. In glacial times sea levels were much lower. All coral would have died, and any coral surfaces would have been eroded by the sea. Once conditions started to warm, and sea level was rising, the previous coral reefs provided a base for the upward growth of coral.
What is the value of coral?
-Seafood, LICs =1/4 of total fish catch; up to a a billion people in Asia on it as main source of protein. If managed sustainably can yield up to 15 tonnes per km2.
-New medicines - currently used for bone grafts and for treating leukaemia, skin cancer and tumours. Thought there could be further benefits from the self-protection element of corals.
-Construction - sand and limestone is used in contstruction.
-Coastal protection - creates a buffer adjacent to shorelines and protect land from storms.
What are coral reefs?
Coral reefs are calcium carbonate structure, made up of reef-building stony corals.
What are the conditions required for coral reef growth?
-No reefs develop where the mean annual temperature is below 20oC; optimal conditions for growth are between 23oC and 25oC.
-Most reefs grow in depths of water less than 25m, an so they are generally found on the margins of continents and islands. Coral reefs prefer shallow water because the tiny photosynthetic algae (zooxanthellae) that live in the coral need light to remove waste such as carbon dioxide and supply the coral polyps with as much as 98% of their food requirements.
-Corals are intolerant of water with salinity levels below 32 psu, although they can tolerate high salinity levels (>42 psu) as found in the Red Sea and Persian Gulf.
-Coral reefs generally prefer strong wave action, which ensures oxygenated water, and where there is a stronger cleansing action, which helps remove ay tapped sediment and also supplies microscopic plankton to the coral. However, storm conditions (e.g. the South Asian tsunami) may create waves that are too destructive for the coral to survive.
