India has four coral regions and each one is reached differently

Reefs need conditions most of the Indian coast cannot supply

Reef-building corals live in partnership with algae inside their own tissue, and those algae need light. That single requirement sets almost all of the limits: the water has to be shallow, clear enough for light to penetrate, warm through the year, and free of the heavy sediment that rivers deliver.

Most of the Indian mainland coast fails at least one of those tests, because it is fed by large rivers carrying enormous quantities of silt. Where reefs do occur, it is where rivers are absent or small.

The result is four broad regions: the Gulf of Kachchh in the northwest, the Gulf of Mannar and the Palk Bay in the far south, the Lakshadweep atolls in the Arabian Sea, and the reefs around the Andaman and Nicobar Islands. They are not variations on one thing; they differ in structure, in accessibility and in condition.

Fringing reefs, atolls and the difference between them

A fringing reef grows outwards from a shore, so it is shallow, close in and reachable by wading or by a short boat trip. The reefs of the Gulf of Mannar and the Gulf of Kachchh are of this type, and both sit in water that is heavily influenced by the mainland.

An atoll is a ring of reef around a lagoon with no land in the middle except the low sand islands the reef itself has built. The Lakshadweep group is a set of these, and they sit far offshore in clear oceanic water, which is why the colour of the lagoons there is what it is.

The Andaman and Nicobar reefs are mostly fringing reefs around continental islands, and being remote from big rivers and big cities they include some of the least disturbed reef in the region. Getting to any of them is a capacity problem before it is anything else, because these are places reached by a limited number of flights and sailings.

A reef is built on the skeletons of the reef before it

The living layer of a coral reef is thin. Underneath it is the accumulated limestone skeleton of previous generations, built up over a very long period, and the structure of a reef is therefore a record of centuries of slow deposition rather than of a single lifetime.

This is what makes physical damage so serious. A fin kick that snaps a branching coral removes growth that took years, and an anchor dropped on a reef flattens a patch that may not recover in a human lifetime. The reef does regrow, but on its own timescale.

It is also why reefs are such productive places. The three-dimensional structure creates an enormous number of hiding places, and the animals that live in and around it are far more abundant than the open water nearby could support.

Bleaching has changed what these places look like

When water stays too warm for too long, corals expel the algae living inside them and turn white. The animal isn’t dead at that point, and if conditions return to normal quickly enough it can recover, but a prolonged event kills large areas of reef.

Indian reefs have been through several serious bleaching episodes in recent decades, and the effects have been uneven — some areas have recovered substantially, others have not. Anyone who saw a particular reef years ago should not assume it looks the same now, in either direction.

The other pressures are local rather than global: sediment from construction and dredging, fishing methods that damage structure, sewage and nutrient runoff feeding algae that overgrow coral. These are the ones that management can act on directly, and where marine parks exist, that is largely what they are for.

Marine life beyond the reefs is a different set of trips

Dugongs, the shy marine mammals that graze on seagrass, survive in Indian waters in small numbers, mainly around the southern gulfs and parts of the Andaman group. They are rarely seen and are strictly protected, and honest operators won’t promise them.

Whale sharks appear seasonally off the Gujarat coast, where a long conservation effort with local fishing communities changed a hunt into a protected presence. Dolphins are far more widely seen, including in some lagoons and estuaries as well as offshore.

For any of it, the practical rules are the same. Marine national parks require permission, the arrangements differ by state and by island administration and change from season to season, and diving requires an operator with real training standards. Check the current position for the specific site, use a boat with a mooring rather than an anchor, do not stand on coral, and take everything back with you.