Decline Of Coral Cover In Lakshadweep – 24-Year Study (1998–2022)

A 24-year-long coral reef monitoring study in the Lakshadweep islands reveals a 50% decline in coral cover since 1998 due to recurring marine heatwaves driven by climate change.

The study named as ‘Local Environmental Filtering and Frequency of Marine Heatwaves Influence Decadal Trends in Coral Composition’, published in the journal Diversity and Distributions

Key Findings

Long-term Decline: Coral cover dropped from 37.24% in 1998 to 19.6% in 2022.

Marine heatwaves are prolonged periods of unusually warm ocean temperatures that disrupt marine ecosystems, coastal livelihoods, and economies.

They typically form during hot, dry, and calm weather, which prevents the mixing of warmer surface waters with cooler layers beneath.

Linked to Climate Events: Decline corresponds with three major ENSO (El Niño Southern Oscillation) events: 1998, 2010, and 2016.
Declining Recovery Rate
- Coral mortality decreased with each successive bleaching event.
- However, recovery rates also dropped, indicating reduced resilience.
- Recovery required a six-year bleaching-free window, which is becoming rare due to frequent heatwaves.
Local Environmental Role:
- Depth, wave exposure, and reef location influenced how corals responded to stress and recovered.
Critical Warnings:
- Local resilience efforts are not enough without urgent global climate action.
- Marine heatwaves are becoming too frequent for reefs to recover.

Coral Bleaching

Coral bleaching occurs when corals experience stress due to changes in environmental conditions—especially temperature rise, light intensity, or nutrient imbalance.
In response, they expel the symbiotic algae (zooxanthellae)living in their tissues. These algae give corals their color and provide essential nutrients through photosynthesis.
When expelled, the corals turn completely white, a condition called bleaching.
Though bleached corals are still alive, prolonged stress can lead to coral death if the algae do not return.

About Corals

Corals are calcareous formations created from the skeletons of tiny marine organisms known as polyps. These polyps extract calcium salts from seawater to build hard protective skeletons.
Over time, as polyps die, new generations grow on their remains, forming colonies anchored to the rocky seafloor.
These colonies grow upward and outward, forming solid calcareous masses called corals.
When these deposits build up in shallow water, they form reefs, which can later evolve into islands.
Corals vary in shape and colour, depending on the minerals present in the surrounding water.

Ideal Conditions for Coral Growth

Latitudinal Range: Found mainly between 30°N and 30°S in tropical waters.
Depth: Prefer shallow waters, around 45–55 metres deep, where sunlight is abundant.
Temperature: Optimal water temperature is around 20°C.
Water Quality: Clear, saline seawater is ideal. Freshwater and highly saline conditions inhibit growth.
Nutrition: Require oxygen and plankton (tiny marine food). Growth is faster on the seaward side due to greater food availability.

Coral Cover

Live coral cover refers to the portion of a reef’s surface occupied by living hard corals. It serves as a key indicator of reef health.
A high coral cover reflects a resilient ecosystem, supporting marine biodiversity, protecting coastlines, and sustaining local fisheries and tourism.

Additional Reading: Coral Bleaching Event

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