Coral Reefs Notes

Coral Reef Formation

  • Coral reefs consist of coral consolidated into limestone.
  • They are the largest structures created by natural activity and the oldest ecosystems.
  • Corals are small animals (polyps) that feed on microscopic plankton using tiny tentacles.
  • Polyps live behind a calcareous skeleton; when they die, the skeletons accumulate over time, forming coral reefs.
  • Coral skeletons have various geometric forms.

Types of Coral Reefs

  • Fringing Reefs: Develop in shallow waters along tropical coasts.
    • Grow upwards to sea level and outwards towards the open ocean.
    • Narrow platforms close to shore without a substantial lagoon.
  • Barrier Reefs: Grow parallel to the coastline, separated by a lagoon.
    • The lagoon develops between the fringing reef and the land.
    • Can originate offshore if the seabed is shallow enough.
  • Atolls: Roughly circular reefs surrounding a deep lagoon.
    • Common in the Indo-Pacific region.

Darwin’s Theory

  • Fringing reefs convert into barrier reefs, and barrier reefs convert into atolls as the land sinks beneath the ocean.

Daly's Glacial Control Theory

  • An island emerges from the sea.
  • Sea levels drop during an Ice Age.
  • Erosion creates horizontal terraces and ledges.
  • As the Ice Age ends, sea levels rise.
  • Coral reefs grow on the newly created submerged platforms.

Conditions Necessary for Coral Growth

  • Temperature: Seawater temperature of 16-35 °C, with optimum temperatures of 23-25 °C.
  • Clean Salt Water: Absence of major rivers bringing silt and fresh water.
    • Excessive silt reduces light and blocks coral mouths.
  • Light: Need light to support symbiotic algae (zooxanthellae) for photosynthesis.
  • Depth: Usually restricted to water depths of less than 70m.

Threats to Coral Reefs

  • 10% of coral reefs are degraded beyond recovery.
  • 30% are in critical condition and may die within 10 to 20 years.
  • 60% of the world's coral reefs may die completely by 2050 if current pressures continue.
  • Natural Threats: Hurricanes, tsunamis, volcanoes, earthquakes, predators, bleaching, and pathogens.
  • Human Threats: Blast fishing, tourism, and pollution.

Specific Threats

  • Hurricanes: cause fresh water poisoning; destroy ecosystems.
  • Tsunamis: cause physical damage; disrupt reproduction.
  • Volcanoes: deposit sediment; increase sea temperature.
  • Blast fishing: destroys surrounding ecosystems.
  • Tourism: pollution from souvenirs and bodily oils

Global Warming Effects

  • Higher sea temperatures cause coral bleaching.
  • Ocean acidification reduces the ability to form skeletons.
  • Sea level rise can make reefs too deep for adequate sunlight.

Consequences of Coral Reef Destruction

  • Loss in biodiversity.
  • Loss of natural coastal protection.

Measures to Protect Coral Reefs

  • Reduce pollution and sedimentation.
  • Reduce over-harvesting and harmful practices.
  • Reduce impacts from tourism and boating.
  • Restore damaged reefs.
  • Increase community awareness through education.

Great Barrier Reef

  • The world's largest reef system (2,900 individual reefs and 900 islands).
  • Greatest threat: climate change causing ocean warming and coral bleaching.
  • Pollution from excessive use of fertilizers.

Importance of Coral Reefs

  • Among the oldest ecosystems on Earth.
  • Support a diversity of species.
  • Provide sources of food and shelter.
  • Important for subsistence, fisheries, tourism, shoreline protection, and medicine development.