CDS (II) 2022 General Knowledge · Question 49 of 120

Correct — C, Andaman and Nicobar Islands. India's reef area was first mapped systematically by the Department of Ocean Development with the Space Applications Centre in 1997, from IRS, Landsat and SPOT imagery, and the four options of this question are simply the four rows of that table: Andaman and Nicobar Islands 959·3 sq km, Lakshadweep 816·1 sq km, Gujarat's Gulf of Kutch 460·2 sq km, and Tamil Nadu's Palk Bay and Gulf of Mannar together 94·3 sq km, out of a national total of about 2,330 sq km. The Andaman and Nicobar group wins because it is not a single reef tract but a chain of some 570 islands strung down roughly 700 km of warm, clear, low-turbidity sea, most of them carrying fringing reef on both flanks, with reef growth continuing all the way to Great Nicobar. Later satellite re-mapping has pushed the Andaman and Nicobar figure towards 1,000 sq km and the national total towards 2,375 sq km, which only widens the lead.

• (a)Gujarat — Gujarat is a real answer to a different question. Its Gulf of Kutch reefs cover about 460 sq km — second on the mainland and by no means small — but the Gulf is turbid, has one of India's largest tidal ranges and sits beside heavy industry, so the reef there is patchy, largely dead-coral platform and among the most degraded in the country. It is under half the Andaman and Nicobar figure.
• (b)Tamil Nadu — Tamil Nadu is the smallest of the four, not the largest. Palk Bay and the Gulf of Mannar together hold about 94 sq km of reef. The Gulf of Mannar is famous — India's first marine biosphere reserve, 21 islands, a marine national park declared in 1986 — but fame is not area, and this question asks only about area.
• (d)Lakshadweep — The strongest trap, and a near miss at about 816 sq km. Lakshadweep feels like the right answer because the whole group is coral — it holds India's only true atolls — but the 36 islands themselves are tiny, none more than about 9 km long, and their combined lagoon-and-reef area still falls short of the Andaman and Nicobar total.

Reef-building corals are colonial animals that live in partnership with single-celled algae called zooxanthellae, which photosynthesise inside the coral's tissue. That partnership fixes where reefs can grow: shallow, clear, sunlit, salty water warmer than about 20 degrees Celsius and free of heavy silt. India's reefs sit in four principal tracts — the Gulf of Kachchh in Gujarat, the Gulf of Mannar and Palk Bay in Tamil Nadu, the Lakshadweep atolls, and the Andaman and Nicobar Islands — with small patch reefs off Malvan and parts of the eastern coast.

This is an area question wearing the costume of a biodiversity question. The instinct is to reach for the name that sounds most coral — Lakshadweep, which is built of coral through and through — or for the Gulf of Mannar, which every environment chapter praises. Area rewards neither. What decides it is the sheer length of coastline available for reef to grow along, and the Andaman and Nicobar archipelago has more of it than the rest of India put together. A second reading aid is in the wording: the stem says States or UTs, and three of the four options are places where the reef is administered by a Union Territory or a single State, so nothing is being hidden there.

• The Department of Ocean Development and Space Applications Centre mapping of 1997 gives Andaman and Nicobar Islands 959·3 sq km of reef, Lakshadweep 816·1, Gulf of Kutch 460·2, and Palk Bay with the Gulf of Mannar 94·3 — a total of 2,329·9 sq km.
• Lakshadweep holds India's only true atolls; the Andaman and Nicobar and Gulf of Mannar reefs are mainly fringing reefs.
• The Gulf of Mannar Marine National Park, declared in 1986, covers 21 uninhabited islands between Rameswaram and Tuticorin.
• Reef corals need clear, shallow water warmer than about 20 degrees Celsius; silt and freshwater inflow are why the Sundarbans coast has no reef at all.
• The Andaman reefs suffered mass bleaching in April and May 2010, when average sea-water temperature touched about 33·8 degrees Celsius against a normal of roughly 30 to 31.

• Ranking reefs by how often they appear in the syllabus rather than by area — the Gulf of Mannar is the most written-about and the smallest of the four.
• Assuming Lakshadweep must lead because it is entirely made of coral; the islands are tiny even though the reef around them is not.
• Adding the Sundarbans to any list of Indian reef sites — silt and fresh water rule reefs out there completely.

Either as a straight ranking of India's four reef tracts, or as a select-the-correct-list item asking which of Gulf of Kachchh, Gulf of Mannar, Lakshadweep and Andaman and Nicobar have coral reefs.

• practice — not a real PYQ

  Which one of the following Indian coral reef areas consists of atolls rather than fringing reefs?

  • (a)Gulf of Kachchh
  • (b)Gulf of Mannar
  • (c)Lakshadweep
  • (d)Andaman Islands

  Answer(c) Lakshadweep — its islands sit on coral atolls, while the Gulf of Mannar and the Andamans carry fringing reefs and the Gulf of Kachchh has patchy platform reef.

• practice — not a real PYQ

  Coral reefs are absent along the Sundarbans coast mainly because of

  • (a)water that is too warm
  • (b)heavy silt and fresh water discharge
  • (c)absence of tidal action
  • (d)excessive salinity

  Answer(b) heavy silt and fresh water discharge — reef corals need clear, saline, sunlit water, and the Ganga-Brahmaputra delta supplies the opposite.