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Which Is the Largest Coral Reef in India? The Four Reef Systems, Ranked and Measured

Which Is the Largest Coral Reef in India? The Four Reef Systems, Ranked and Measured

Author: Rohit Gupta

Published:

Aerial view of the largest coral reef in India, with turquoise lagoons, reef formations and small vegetated islands in the Andaman and Nicobar Islands

India’s largest coral reef system surrounds the Andaman and Nicobar Islands. Both of the datasets in general circulation agree on that, and they agree on the order of the three systems behind it.

They do not agree on how large any of them are.

Search for the biggest coral reef in India and you will be told, quickly and often, that it covers over 1,021 square kilometres. You will rarely be told which survey produced that number, or in what year. What follows gives the ranking, the figures on both sides of the disagreement, and an honest account of where the evidence thins out, which turns out to be exactly where you would least want it to.

India’s Four Coral Reef Systems, Ranked by Size

Two sources run through this section. The first is the mapping attributed to the Space Applications Centre and the Department of Ocean Development, origin of the figures most often quoted online. The second is a technical review published by the Food and Agriculture Organization, drawing on earlier survey work. Neither states the year its survey was carried out.

  1. Andaman and Nicobar Islands. Reported at 1,021 sq km by the first dataset and 959.3 sq km by the second. These are fringing and patch reefs strung along a chain of islands in the Bay of Bengal, with a barrier reef running roughly 320 km down the Andaman west coast.
  2. Lakshadweep. Reported at 934 sq km and 816.1 sq km. Unlike the other three, Lakshadweep’s reefs are atolls, rings of coral around central lagoons, which is one plausible reason the two estimates differ by around 14 per cent. How much lagoon you count changes the answer.
  3. Gulf of Kachchh. Reported at 352 sq km and 460.2 sq km. The gulf appears as both Kachchh and Kutch in the scientific literature, so expect either spelling when checking sources. Note also the direction of the disagreement. This is the only system where the older review reports substantially more reef than the widely circulated figure, and the gap is the largest of the four at roughly 30 per cent.
  4. Gulf of Mannar and Palk Bay. Reported at 76 sq km and 94.3 sq km. Smallest of the four by a wide margin, and, as it happens, the best studied.

Nationally, the most frequently cited total is about 2,375 square kilometres. Add up the four regional figures in the second dataset and you get roughly 2,330. Those totals sit within about 2 per cent of each other, which looks reassuring until you notice that their regional components disagree by up to 30 per cent in opposite directions. The national agreement is arithmetic coincidence, not corroboration.

These four are where India’s mapped reef area is concentrated, not everywhere coral grows in the country. The Indian National Centre for Ocean Information Services also identifies coral at Malvan on the Maharashtra coast, which neither dataset ranks. Readers who want to know where these reefs are and what visiting them is like will find that ground covered in the Ocean Evoke location guide, Coral Reefs of India: A Complete Location Guide.

Why the Coral Reef Area in India Is Hard to Pin Down

None of this means somebody has blundered. Reef mapping is genuinely difficult, and the differences are methodological.

A reef has no neat edge. Satellite resolution determines how much fine structure gets counted, tidal state at the moment of capture changes what is visible, and survey year matters because reefs change. Most significantly, different surveys draw the boundary of “reef” in different places. Do you count the intertidal reef flat that sits exposed at low tide? The rubble field behind it? The lagoon inside an atoll?

Consider the Gulf of Kachchh, which shows how much that last question matters. The same FAO review that puts the gulf at 460.2 sq km separately reports that the reef flat there occupies 136.5 sq km on its own. Include or exclude that single feature and you have moved the total by an amount close to the entire disagreement between the two datasets.

So the honest formulation runs like this. The ranking is stable, because two independently produced datasets built from different surveys put the four systems in the same order. The magnitudes are estimates, they carry no survey year in any source that repeats them, and they should be read as approximate.

Reef Area Is Not Living Coral

A second confusion sits inside every one of those figures, and it matters more than the disagreement between them.

Area measures a structure. Living coral cover measures what is alive on it. A reef mapped at 1,021 square kilometres is not 1,021 square kilometres of living coral, and no source consulted here reports what share of India’s mapped reef area currently carries live coral.

The two measures move independently. The FAO review gives the Gulf of Kachchh an extent of 460.2 sq km while noting that living coral there rarely exceeds 20 to 30 per cent of it, a description now some years old. Lakshadweep’s reefs are called excellent off the uninhabited islands and endangered along the inhabited ones, which describes condition rather than area.

Generations of coral lay down calcium carbonate over centuries to build a reef, a process covered in the companion article Coral Reef Formation: How Reefs Are Built (and Destroyed). That limestone architecture outlasts the animals that made it, so a reef can be structurally intact and biologically hollowed out at once, and from a satellite it may look much the same.

Where the Shrinking Has Actually Been Measured

Now the difficult part. India has no verified national time series of reef area built on a consistent method, so no reliable figure exists for how fast the country’s reefs are shrinking overall. What exists is strong evidence from two systems.

Lakshadweep: Nearly Half the Living Coral, Gone in 24 Years

The most complete Indian record comes from Lakshadweep. Researchers from the Nature Conservation Foundation and the Centre for Advanced Studies of Blanes monitored 12 reef sites across three atolls, Agatti, Kadmat and Kavaratti, continuously from 1998 to 2022. Their analysis appeared in the journal Diversity and Distributions in July 2025.

Live coral cover across those sites fell from 37.24 per cent in 1998 to about 19.6 per cent in 2022. That amounts to a loss of 47.3 per cent of the living coral, in a quarter of a century, at sites chosen for monitoring rather than for damage.

The cause the study identifies is heat. Three marine heatwaves, tied to El Niño events in 1998, 2010 and 2016, account for the step changes in the record. A marine heatwave is not a hot afternoon but a prolonged spell of unusually warm water, and duration is what does the killing.

Two findings from that work deserve more attention than they usually get.

The first concerns recovery time. These reefs needed a minimum of roughly six years without a new bleaching event before recovery became significant, and fast-growing corals such as Acropora cannot rebuild in less. As heatwaves grow more frequent, that six-year window is closing. One of the co-authoring institutions describes it as increasingly unattainable.

The second is a warning against optimism. Coral mortality fell with each successive bleaching event, which sounds like adaptation. The researchers read it differently. Heat-sensitive species had largely gone already, so less coral died because less coral remained that could die. What survives is dominated by tougher, slower, structurally simpler genera such as Porites. That is not a reef recovering but a reef simplifying.

The Gulf of Mannar: Both Measures Falling

Tamil Nadu holds the other long record, and it is the one place where reef area itself has been tracked over time. A two-decade assessment by the Suganthi Devadason Marine Research Institute with the Government of Tamil Nadu, published in January 2025, reports the reef area of the Gulf of Mannar falling from 11,060 hectares in 2005 to 6,628 hectares in 2021, a loss of 4,432 hectares, or roughly 40 per cent of what was there in 2005. Much of the lost ground is now dominated by macroalgae or seagrass, and seaweed cover makes it harder for new coral larvae to settle, which is part of why such losses compound. The Ocean Evoke article Gulf of Mannar Coral Reef: India’s Forgotten Reef covers this system in more depth.

Live coral cover in the same waters tells a more complicated story, and the middle of it is the interesting part.

  • 2005: 37 per cent
  • 2009: 42.9 per cent
  • 2021: 27.3 per cent

Cover rose before it fell. The assessment attributes that rise to the ending of coral mining in the gulf, banned in 2005. The subsequent fall follows the global bleaching events of 2010 and 2016, with the Mandapam group hit harder than the Keelakarai and Tuticorin groups.

What We Do Not Know About the Largest Coral Reef in India

Here is the uncomfortable finding, worth stating plainly rather than leaving out.

The two systems described above rank second and fourth. The largest, Andaman and Nicobar, is the one whose current condition is hardest to establish. Bleaching in those islands has been studied and published, but the papers sit behind publisher paywalls that could not be accessed for this article, and the summaries available in their place report figures for the 2010 event ranging from 60 per cent to over 80 per cent of corals affected, with no way to reconcile them. No percentage for Andaman appears here, because there is not a defensible one to give.

That gap is real, and not only for a writer. Take the two datasets above and calculate: Andaman and Nicobar accounts for roughly 41 to 43 per cent of India’s mapped reef area, a share worked out from the figures already given rather than published anywhere as such. The single largest holding of Indian reef is also the one a general reader can learn least about from freely available sources.

What Is Killing India’s Coral

Across both well-documented systems, in two different seas, the dominant driver is heat.

Corals live with microscopic algae inside their tissue, which supply most of their food. When water stays too warm for too long, the coral expels those algae and turns white. That is bleaching, and a bleached coral is not yet dead but starving. Should the heat pass soon enough, the algae return and the coral recovers. If it does not, the coral dies.

Local pressures sit on top of that, and they are the ones within reach of policy: coral mining and quarrying, sedimentation from rivers and construction, sewage and industrial discharge, destructive fishing including bottom nets and explosives, anchor damage and trampling by visitors, coastal development, invasive seaweed such as Kappaphycus alvarezii in the Gulf of Mannar, and disease outbreaks. None of these matches heat in scale. All of them make heat more lethal, because a reef already weakened locally has less capacity to survive a bad summer.
Coral bleaching in India shown across four stages, from healthy branching coral to severely degraded coral

The One Number That Went Up

Return to that Tamil Nadu series for a moment, because it holds the most useful fact here.

Between 2005 and 2009, live coral cover rose from 37 per cent to 42.9 per cent. The surveying institution attributes that rise to the ending of coral mining. This is the institution’s own reading rather than a controlled experiment, and it deserves that qualification. Even so, it is the closest thing available to a natural test of whether local action changes anything, and the answer it returns is yes.

Read the rest of the series just as carefully. Cover fell to 27.3 per cent by 2021, well below where it started. Ending coral mining did not save these reefs. What it demonstrated, in measurable form, is that a reef relieved of one local pressure begins rebuilding within a few years, and that these reefs were not simply doomed by global conditions regardless of what anyone did nearby.

What Restoration Can and Cannot Do

Restoration work runs across all four systems, and the reported results are encouraging at the scale they operate.

The longest-running programme, in the Gulf of Mannar since 2002, has deployed 5,550 artificial substrates and transplanted about 51,000 coral fragments of 20 native species across 40,000 square metres, with reported survival between 55 and 80 per cent. At Mithapur in Gujarat, a project running since 2008 reports 2,310 artificial reef modules and 57 coral nurseries across 5,867 square metres, with survival of rescued corals at around 96 per cent. These figures are self-reported by the organisations doing the work, and no independent audit of them was found.

Now the scale. Forty thousand square metres is 0.04 square kilometres, against roughly 44 square kilometres of reef lost in the same gulf over an overlapping period. The ratio is about one to a thousand.

None of which argues against restoration. Transplanted corals seed recovery, artificial structures accumulate species over time, and the techniques being proven now are the ones that will matter if and when the water stops getting hotter. The argument is against treating restoration as an answer to the loss. At current scale, this is a holding action and a laboratory, not a repair.

Conclusion

India’s largest coral reef lies in the Andaman and Nicobar Islands, and the ranking behind that answer is more solid than any individual number in it. The figures you will find quoted come from undated surveys that disagree by up to 30 per cent, and the widely repeated 1,021 square kilometres is one estimate among two rather than a settled measurement.

Where the reefs have been watched properly, they have lost a great deal. Lakshadweep’s monitored sites have shed nearly half their living coral in 24 years. In the Gulf of Mannar, roughly 40 per cent of the reef area has gone since 2005. Heat is the principal cause in both, and the local pressures that scientists and administrators can act on are what determine whether a reef survives the next hot summer.

The most striking thing to come out of this research is not any single figure. Rather, it is that the country’s largest reef system is also its least legible to an ordinary reader, while the smallest is the best documented. We know most about the reef we have already damaged most and then chosen to study, and least about the one holding the largest share of what remains.

What would we be doing differently if the Andaman and Nicobar reefs were measured as closely as the Gulf of Mannar has been?

Sources

Aqua Lung
Canon
Go Pro
Ikelite
Insta 360
Mares
Nauticam
PADI
Shearwater
TDI
Rotary Club of Calcutta South CIty
Kuddle Life Foundation
Coastal Impact