Coral reefs coral bleaching | Oceanography | Principle Of Geography

 

Oceanography

Principle Of Geography

Geography Complete Study Material

(Paper - I)

Coral reefs and Coral bleaching

Coral reefs

             Coral reefs are large underwater structures composed of the skeletons of colonial marine invertebrates called coral. Corals are of two types: Hard coral and Soft coral. The coral species that build reefs are known as herma typic, or “hard,” corals because they extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. Other species of corals that are not involved in reef building are known as “soft” corals. Soft corals, such as sea fingers and sea whips, are soft and bendable and often resemble plants or trees. These corals do not have stony skeletons, but instead grow wood-like cores for support and fleshy rinds for protection. Deep-sea corals live in much deeper or colder oceanic waters and lack zooxanthellae. Unlike their shallow water relatives, which rely heavily on photosynthesis to produce food, deep sea corals take in plankton and organic matter for much of their energy needs.

              Corals are nothing but calcareous rocks, formed from the skeletons of minute sea animals, called polyps. The polyps extract calcium salts from seawater to form hard skeletons which protect their soft bodies. These skeletons give rise to corals. The corals live in colonies fastened to the rocky seafloor. New generations develop on skeletons of dead polyps. The tubular skeletons grow upwards and outwards as a cemented calcareous rocky mass collectively called corals. The shallow rock created by these depositions is called a reef. These reefs, later on, evolve into islands. The corals Occur in different forms and colours, depending upon the nature of salts or constituents they are made of. The progressive development of corals appears over the sea surface in different forms over a period of time. Small marine plants (algae) also deposit calcium carbonate, thus contributing to coral growth.

Types of Coral reefs

                 Coral reefs can be classified on the basis of large-scale reef morphology; the size and shape of a reef, and its relation to nearby land (if any). This is usually (but not always) sufficient to clearly distinguish one type from the others. There is often a great deal of overlap among the major reef types (within a given biogeographic region) in terms of the dominant groups of animals and plants, as well as their ecological interactions. There are three major types of coral reefs: 

• Fringing Reef, 
• Barrier Reef, and 
• Atoll

Location of Coral reefs

                     The majority of reef-building corals are found within tropical and subtropical waters. These typically occur between 30° north and 30° south latitudes. The Indonesian/Philippines archipelago has the world’s greatest concentration of reefs and the greatest coral diversity. Other areas of reef concentration are the Great Barrier Reef of Australia, the Red Sea, and the Caribbean, the latter having a much lower diversity than all major Indo-Pacific regions. Most reefs are located between the Tropics of Cancer and Capricorn, in the Pacific Ocean, the Indian Ocean, the Caribbean sea. World’s major coral reef regions: 

• Caribbean/ western Atlantic 
• Eastern Pacific 
• Central and western Pacific 
• Indian Ocean 
• Arabian Gulf 
• Red Sea

Coral bleaching

             When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn Coral bleaching. Corals begin to starve once they bleach. While some corals are able to feed themselves, most corals struggle to survive without their algae. If conditions return to normal, corals can regain their algae, return to their normal colour and survive. However, this stress is likely to cause decreased coral growth and reproduction, and increased susceptibility to disease. Bleached corals often die if the stress persists. Coral reefs that have high rates of coral death following bleaching can take many years or decades to recover.

Causes of Coral bleaching

              As coral reef bleaching is a general response to stress, it can be induced by a variety of factors, alone or in combination. It is therefore difficult to unequivocally identify the causes for bleaching events. The following stressors have been implicated in coral reef bleaching events :

• Temperature
• Solar Irradiance
• Subaerial Exposure
• Fresh Water Dilution