Coral Reefs

Mains Marks Booster     5th August 2023        

Coral reefs are intricate ecosystems built by thousands of small animals known as coral polyps, which are closely related to anemones and jellyfish. 

Formation of Coral Reefs

  • Coral polyps have soft bodies covered by calcareous skeletons that they create by extracting calcium salts from seawater. These polyps live in colonies attached to the rocky sea floor.
  • The tubular skeletons grow upwards and outwards, forming a cemented calcareous rocky mass collectively known as corals. When coral polyps die, they shed their skeletons, which serve as the foundation for new polyps to grow.
  • Over millions of years, this cycle repeats, resulting in the accumulation of coral layers, known as reefs. Different stages of coral deposition give rise to various marine landforms, with coral reefs being one of the most important.

 Types of Coral Reefs

Types of Coral Reefs

Ideal Conditions and Ecological Causes

  • Coral reefs thrive under stable climatic conditions with perpetually warm tropical waters (around 20°C). They require shallow depths for sufficient sunlight, clear saltwater, abundant plankton, and minimal pollution.
  • The growth of corals is facilitated by a symbiotic relationship with zooxanthellae, single-cell algae that live within coral polyp tissues.
  • Coral bleaching, which can lead to coral death, can occur due to various disturbances such as temperature changes, subaerial exposure, freshwater dilution, inorganic nutrients, xenobiotics, and epizootics.
  • Bleaching can be beneficial under low-stress conditions, as corals may develop resistance. 

Spatial and Temporal Range of Coral Reef Bleaching

  • Coral bleaching events have been observed in major coral reef regions worldwide, including the Caribbean/western Atlantic, eastern Pacific, central and western Pacific, Indian Ocean, Arabian Gulf, and Red Sea.
  • Prior to the 1980s, most coral mortality was due to non-thermal disturbances, but since then, bleaching events have occurred on a larger scale and at greater depths.
  • Recent research suggests that corals exposed to low levels of stress may develop resistance to bleaching. 
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