Maarg Manthan · Topic 9.10

Threats to and Conservation of Coral Reefs

Environment & Ecology › Coastal and Wetland Ecosystems · Topic 9.10

Coral reefs face threats from both global climate pressures and local human activity. The most serious global threats are marine heat waves, which cause coral bleaching when stressed corals expel their symbiotic algae, and ocean acidification, which lowers the carbonate that corals need for their skeletons. Local threats include land-based pollution and sewage, sediment from coastal construction and dredging, nutrient runoff, overfishing and destructive fishing with dynamite and cyanide, coral mining for lime and building material, careless tourism and anchoring, outbreaks of the crown-of-thorns starfish, and coral diseases. Mass bleaching events were recorded in 1998, 2010, in 2014 to 2017 and again in 2023 to 2024, which the US NOAA described as a fourth global bleaching event. In India, all reef-building corals are in Schedule I of the Wildlife (Protection) Act, 1972, reefs fall in CRZ-I, and many reefs lie in marine parks and biosphere reserves.

5 min read · UPSC Prelims · Environment & Ecology · Coastal and Wetland Ecosystems

At a Glance

Top threat Bleaching from heat
Chemistry Ocean acidification
Local threats Pollution, dynamite, mining
Indian law Schedule I, CRZ-I
Global body ICRI
Exam link UPSC Prelims, Environment & Ecology: Coastal and Wetland Ecosystems

Where Does It Fit?

This topic completes the coral reef sequence. It joins the biology and technology of reefs to the problem of climate stress and marine pollution, and it leads to the topics on wetlands. Previous topic: Concept of Bio-Rock Reefs. Next topic: Wetlands: Definition, Types and Importance.

What Threatens Coral Reefs?

Threat	How it harms reefs
Marine heat waves and bleaching	Warm water stresses corals, which expel zooxanthellae and turn white; long heat can kill them
Ocean acidification	Extra carbon dioxide dissolved in sea water lowers pH and carbonate ions, weakening coral skeletons
Sedimentation and pollution	Silt blocks light; sewage and fertiliser feed algae that smother corals
Destructive fishing	Dynamite, cyanide and bottom nets break reefs and kill fish
Coral mining	Corals are taken for lime and construction
Crown-of-thorns starfish	Outbreaks eat large areas of live coral
Tourism and shipping	Anchors, trampling, oil and boat strikes damage reefs

How Are Reefs Conserved?

Cut emissions: limiting warming is the main way to reduce bleaching
Marine protected areas: Gulf of Mannar, Gulf of Kutch and Wandoor protect reef sites
Legal protection: reef corals are in Schedule I of the Wildlife (Protection) Act and reef areas are CRZ-I
Pollution control: treat sewage and regulate coastal construction and dredging
Sustainable fishing: ban dynamite and cyanide, and manage fishing near reefs
Restoration: coral gardening, bio-rock and artificial reefs
Monitoring: reef surveys and satellite heat stress alerts
Community involvement: fisher groups and alternative livelihoods like seaweed farming

What Else Should You Remember?

Bleaching: corals turn white when they lose zooxanthellae; they can recover if temperatures fall soon
Degree heating weeks: a measure used by NOAA to track heat stress on corals
El Nino: a warm phase in the Pacific that has triggered many mass bleaching events
Mass bleaching years: 1998, 2010, 2014 to 2017 and 2023 to 2024
Acidification: about a quarter of human carbon dioxide emissions dissolve in the ocean, lowering pH
Sea level rise: can help or harm depending on how fast corals grow
Storms: strong cyclones break coral structures
Coral diseases: black band and white band diseases spread in stressed reefs
Land-based pollution: most reef damage near coasts comes from land
Overfishing of herbivores: fewer parrotfish and surgeonfish let algae overgrow corals
Gulf of Mannar: coral mining and destructive fishing were major threats, now curbed by protection
Gulf of Kutch: industrial and port pollution and sedimentation are concerns
Lakshadweep: bleaching during heat waves and sea level rise are key risks
Andaman and Nicobar: the 2004 tsunami and bleaching in warm years damaged reefs
Schedule I: reef-building corals are listed in Schedule I of the Wildlife Protection Act
CRZ-I: coral reefs and surrounding areas are ecologically sensitive coastal zones
ICRI: International Coral Reef Initiative, a partnership of governments and organisations started in 1994
GCRMN: Global Coral Reef Monitoring Network, which reports on reef status
UNEP Coral Reef Unit: UN support for coral reef action
Reef Check: volunteer survey programme
Coral nurseries: coral fragments grown in underwater nurseries and replanted
Heat-tolerant corals: research on selecting corals that survive warmer water
Reef tourism rules: limits on divers, no anchoring zones and mooring buoys
Link to previous: see Concept of Bio-Rock Reefs
Link to next: see Wetlands: Definition, Types and Importance
Caution: global bleaching statistics are updated often, and wildlife schedules were revised in 2022, so check NOAA, GCRMN and the current Act
Exam hint: learn bleaching, acidification and Schedule I together
Recovery time: a reef hit by severe bleaching may take a decade or more to recover if it is not hit again
Refugia: cooler or deeper reef patches that stay healthier in heat waves are prioritised for protection
Reef-safe sunscreen: chemicals in some sunscreens are linked to coral stress, so some places restrict them
Plastic waste: plastic on reefs raises the risk of coral disease
Seaweed farming: an alternative income for fishers in the Gulf of Mannar when done in non-reef areas

Why Does It Matter for the Exam?

Top threat: Bleaching
Law: Schedule I, CRZ-I
Body: ICRI
Current affairs link: Fourth global bleaching event
Common errors: treating bleaching as death or confusing acidification with warming

As an analytical point, reefs face a double problem: warming stress that no local rule can stop and local damage that local action can reduce. Healthy, well-protected reefs resist heat better, so local action buys time while emissions are cut.

Why Is This Topic Important?

Global Heat, acid
Local Pollution, fishing
Fix Cut emissions, protect

What Came Next?

The next topic covers wetlands: definition, types and importance. Next topic: Wetlands: Definition, Types and Importance.

Key People and Terms

Bleaching Loss of coral algae
Acidification Fall in ocean pH
Crown-of-thorns Coral-eating starfish
ICRI Coral reef partnership
GCRMN Reef monitoring network
Coral gardening Nursery restoration

Exam Corner

Points to Remember

Bleaching: loss of zooxanthellae.
Corals are in Schedule I.
Reefs are CRZ-I.
ICRI began in 1994.
Fourth global event: 2023 to 2024.

Do Not Confuse With

Bleaching and acidification Heat stress versus lower pH
ICRI and GCRMN Partnership versus monitoring network
Bleaching and death Stress state versus mortality

Memory Hook

Heat bleaches, acid thins, fishing breaks, law and care remake.

Mains Angle

Questions ask for threats and protection. These points help.

Threats Global and local
Law Schedule I
Way Emissions, MPAs

A Question You May Face

An original practice question, not a past paper question.

“Discuss the major threats to coral reefs and the measures taken to conserve them, with reference to India.”

How to Answer

Value Reefs.
Threats Heat, local.
Law India.
Way Cut, protect.

GS Relevance

Prelims: bleaching, acidification, legal protection. GS Paper 3: climate change effects and conservation.

Frequently Asked Questions

What is coral bleaching?

Coral bleaching happens when corals under stress, mainly from unusually warm water, expel the zooxanthellae algae living in their tissue. Without the algae the coral turns white and loses its main food source. If temperatures fall soon enough, corals can regain algae and recover, but long stress can kill them.

How does ocean acidification harm corals?

The ocean absorbs a large share of the carbon dioxide released by human activity. This lowers the pH of sea water and reduces the carbonate ions that corals need to build their skeletons, so they grow more slowly and reefs become weaker and more easily eroded.

What local activities damage coral reefs?

Local damage comes from sewage and farm runoff, sediment from dredging and construction, dynamite and cyanide fishing, overfishing of grazing fish, coral mining for lime, anchoring and careless tourism. These pressures weaken corals and make them less able to survive heat waves and disease.

How does Indian law protect coral reefs?

Reef-building corals are listed in Schedule I of the Wildlife (Protection) Act, 1972, which gives the highest protection. Coral reef areas are ecologically sensitive CRZ-I zones under the Coastal Regulation Zone Notification, and many reefs lie in marine national parks and biosphere reserves such as the Gulf of Mannar.

What is the International Coral Reef Initiative?

The International Coral Reef Initiative, started in 1994, is a partnership of governments and organisations that promotes action to conserve coral reefs and related ecosystems. It works to raise awareness, share information and support management, and its work links with the Global Coral Reef Monitoring Network.

PYQ Practice — Statement Analysis

1 Coral bleaching occurs when corals lose their symbiotic algae.

True

Called zooxanthellae.

2 Reef-building corals are in Schedule IV of the Wildlife Protection Act.

False

They are in Schedule I.

3 Ocean acidification weakens coral skeletons.