9 Feb 2024 : Daily Answer Writing

Q1) Healthy coral reefs are among the most biologically diverse, ecologically vital and economically valuable ecosystems on earth. Elaborate upon the significance of coral reefs. Describe the suitable conditions for their health and the threats faced by them.

(250 Words/ 15 Marks)


Healthy coral reefs are an underwater ecosystem consisting of a diverse array of corals, fish, invertebrates, and other marine organisms. The corals are the large underwater structures made from the colonies of marine invertebrates called coral polyps that secrete calcium carbonate skeletons.

As the coral polyps die and new polyps settle and grow on top of the old skeletons, the reef structure gradually builds up and over time creates a massive ecosystem.

The significance of coral reefs is as follows:

  1. Biodiversity: Coral reefs are home to over 25% of all known marine fish species, while covering 1% of ocean. The complex structure of the reef provides habitats for thousands of other species, from tiny plankton to large sharks.
  2. Ecological importance:
  3. Zooxanthellae remove CO2 from the water, making coral reefs an important carbon sink. It is estimated that coral reefs are responsible for removing up to 30% of the CO2 produced by humans.
  4. Corals play a salient role in the process of nutrient recycling.
  5. They protect coastlines from storms and erosion. They protect mangroves and seagrass from tropical cyclones.
  6. Economic value: Coral reefs generate economic benefits by supporting fishing, tourism, and other industries. They provide jobs, income, and food security for millions of people.


Following conditions are suitable for the health of coral reefs:

  1. Warm water: Most coral species thrive in warm water with temperatures between 23-29 degrees Celsius. Water temperatures outside this range can cause stress to corals, leading to bleaching, disease, and death.
  2. Shallow water:
  3. Shallow water provides for clear water with sufficient light penetration which helps the coral polyps to photosynthesize and grow.
  4. Corals require a steady supply of oxygen for respiration. In shallow water, the water is typically well-mixed and oxygenated, which supports healthy coral growth and metabolism.
  5. Stable water chemistry: Corals require a stable and balanced pH level, as well as appropriate levels of calcium carbonate and other minerals in the water to build their calcium carbonate skeletons.
  6. Low nutrient levels: Coral reefs thrive in nutrient-poor waters, as excess nutrients can cause an overgrowth of algae that can suffocate the coral.
  7. High salinity: Corals require very saline water, ranging from 32 to 42 ppt; fresh water ingress can lead to coral bleaching.


However, coral reefs are under threat from a range of factors as discussed below:

  1. Sedimentation and pollution from human activities such as coastal development, deforestation, nutrient pollution, sewage, and mining undermine delicate conditions for the health of coral reefs.
  2. Physical damage:
  3. Coral reefs are fragile ecosystems prone to physical damage from ship anchor, fishing gear, and recreational activities like snorkelling and diving.
  4. Tropical cyclones can cause great physical damage to coral reefs from the impact of waves in the shallow water.
  5. Temperature:
  6. Global warming: Rising sea temperatures are causing mass bleaching events. Coral bleaching occurs when stressed zooxanthellae leave the corals. Mass bleaching happens when high temperatures sustain for long periods.
  7. Increase in sea surface temperature due to El-Nino or extreme weather events like marine heat waves etc., can cause coral bleaching.
  8. Ocean Acidification: Increasing carbon dioxide in the atmosphere is being absorbed into the ocean. The resulting decrease in pH has been reducing calcification rates for reef-building.

To maintain healthy coral reefs, it is important to protect them from threats and sustain conditions that support growth and resilience of coral reefs. Conservation efforts can include measures such as reducing carbon emissions, restricting and regulating fishing and other human activities around coral reefs, and improving waste management practices.

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