CDS (II) 2020 General Knowledge · Question 30 of 120

Correct — D, Kyushu Island, Japan. Kyushu is the third largest and most southerly of Japan's four main islands, 36,782 square kilometres of continental crust carrying a population of over twelve million, shaped by tectonics and volcanism rather than by coral. It also lies too far north for reef building: reef corals need water that stays warm through the year, broadly above eighteen degrees Celsius, which confines true reefs to roughly thirty degrees north and south of the Equator, and Kyushu straddles thirty-one to thirty-four degrees north. The other three all belong to the coral world. The Great Barrier Reef is the largest coral reef system on Earth, running more than 2,300 km off north-east Australia. The Rainbow Reef lies in the Somosomo Strait between Taveuni and Vanua Levu in Fiji and is one of the best known coral dive sites in the South Pacific. Swaraj Dweep, the island in Ritchie's Archipelago renamed from Havelock Island in December 2018, is ringed by the fringing reefs of the Andamans, which are among the richest reef areas in India.

• (a)Great Barrier Reef, Australia — The world's largest coral reef system, over 2,300 km long off the Queensland coast, and the standard example of everything the question means by coral reef.
• (b)Rainbow Reef, Fiji — A coral reef in the Somosomo Strait between the Fijian islands of Taveuni and Vanua Levu, famous for the dive site called the Great White Wall.
• (c)Swaraj Island, India — Swaraj Dweep, the former Havelock Island in Ritchie's Archipelago of the Andamans, renamed in December 2018. Its waters carry the fringing reefs that make the Andaman and Nicobar Islands India's largest reef area.

Reef-building corals are colonial animals that live in partnership with photosynthetic algae, so they need warm, clear, shallow, salt water with plenty of light. That combination restricts them to the tropical belt, away from major river mouths and from cold currents. Darwin's classification sorts the results into fringing reefs, which lie against the shore; barrier reefs, separated from land by a lagoon; and atolls, rings of reef around a lagoon where the central island has subsided. India's reefs are of the first and third kinds: fringing reefs around the Andaman and Nicobar Islands, in the Gulf of Mannar and the Gulf of Kachchh, and atolls in Lakshadweep.

The stem is loosely worded and it is worth saying so plainly: the Great Barrier Reef and the Rainbow Reef are reefs, not islands, and Swaraj Dweep is a continental-type island that has reefs around it rather than an island built by coral. So none of the four is strictly a coral reef island in the technical sense that an atoll islet is. What the question is really asking is which of the four names has nothing to do with coral at all, and on that reading the answer is unambiguous. Kyushu, at over thirty degrees north with twelve million people and a chain of active volcanoes, is the one name in the list that belongs to a different kind of geography altogether.

• Kyushu is the third largest of Japan's four main islands, 36,782 square kilometres, with a population of over twelve million.
• Reef-building corals require water generally warmer than about eighteen degrees Celsius all year, which restricts reefs to roughly thirty degrees north and south.
• The Great Barrier Reef, off north-east Australia, is the largest coral reef system in the world, over 2,300 km long.
• The Rainbow Reef lies in the Somosomo Strait between Taveuni and Vanua Levu in Fiji.
• Havelock Island was renamed Swaraj Dweep in December 2018, together with Neil Island as Shaheed Dweep and Ross Island as Netaji Subhas Chandra Bose Dweep.

• Assuming that anything called a reef must be an island. The Great Barrier Reef and the Rainbow Reef are reefs, not islands.
• Forgetting that Swaraj Dweep is the former Havelock Island, so the new name alone can make it look unfamiliar.
• Overlooking latitude. Coral reefs are a tropical phenomenon, and Kyushu lies beyond the belt.

As an odd-one-out item among reef locations, or as a conditions-for-coral-growth item, or as a which-Indian-areas-have-coral-reefs item.

• practice — not a real PYQ

  Which one of the following is the correct sequence in Darwin's explanation of the development of coral reefs?

  • (a)Atoll, barrier reef, fringing reef
  • (b)Fringing reef, barrier reef, atoll
  • (c)Barrier reef, atoll, fringing reef
  • (d)Fringing reef, atoll, barrier reef

  Answer(b) Fringing reef, barrier reef, atoll — as the central island subsides, the reef keeps growing upward and the lagoon between reef and land widens until only a ring remains.

• practice — not a real PYQ

  Coral reefs in India are found in all of the following EXCEPT which one?

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

  Answer(c) Sunderbans — heavy silt and fresh water from the Ganga-Brahmaputra delta make the water too turbid and too brackish for reef corals.