Which one of the following does NOT illustrate the importance of the Coral Reef?

Correct — D, They protect communities from earthquakes. A reef is a limestone ridge built on the sea floor by colonial polyps. It sits on the crust; it is not part of it, and nothing about a coral framework damps the ground shaking that an earthquake sends through rock. Reefs do absorb wave energy, which is why the other three options are all genuine reef benefits, but wave energy and seismic energy are different things travelling through different media. Even for a tsunami — the one earthquake consequence a reef can blunt — the reef works on the water, not on the quake, and only the wave reaches it.

• (a)They provide employment to the people — This is a real reef benefit. Reef fisheries and reef tourism are the livelihood of coastal communities from the Gulf of Mannar to Lakshadweep, and the Gulf of Mannar reefs alone support fishing villages whose catch depends on reef-associated species.
• (b)They supply building materials — Also real, and the reason it is worded as a benefit rather than a threat. Coral limestone has been quarried for lime, mortar and walls for centuries across the Lakshadweep and Maldive islands, where there is no other local stone.
• (c)They protect shoreline from storms — The best-established reef service of all. A reef crest forces waves to break offshore and strips most of their energy before the water reaches the beach, which is why reef-fronted coasts erode far less in a cyclone than open ones.

Reef-building corals are colonial animals that live with photosynthetic algae in their tissues and lay down a calcium carbonate skeleton. Generation on generation of skeletons cements into a ridge that grows towards the light and towards the open sea. Because the ridge stands in shallow water across the path of incoming swell, it does mechanical work on waves — and because it is alive, it also feeds an ecosystem that supports fisheries and tourism.

This is a NOT question with three easy options and one that sounds vaguely protective. The trap is that 'protect' appears in both option (c) and option (d), and a candidate reading quickly can accept the second because the first was true. Separate the hazard from the medium and the item collapses: reefs act on water, so they help against waves, storm surge and to a limited extent tsunami run-up; an earthquake is ground motion, and no marine structure interferes with it. As of the 2020 exam India's reefs were concentrated in four areas — the Gulf of Mannar, the Gulf of Kachchh, Lakshadweep and the Andaman and Nicobar Islands. The position on option (b) has since hardened: reef-forming corals are protected under the Wild Life (Protection) Act, 1972, so quarrying reef rock for building is now an offence rather than a customary practice.

• Reef corals need warm, shallow, clear, saline water, which confines them to roughly 30 degrees north and south of the equator.
• The reef crest breaks waves offshore and dissipates most of their energy, giving the coast behind it measurable protection from storm surge.
• India's four principal reef areas are the Gulf of Mannar, the Gulf of Kachchh, Lakshadweep and the Andaman and Nicobar Islands.
• Reefs cover a very small fraction of the ocean floor yet host a disproportionate share of marine species, which is what makes reef fisheries productive.
• Bleaching happens when heat stress makes the polyps expel their symbiotic algae; the colony can survive briefly but starves if the stress lasts.

• Reading 'protect' in two options and accepting both because the first one was true.
• Assuming a reef stops a tsunami outright; it reduces run-up, it does not cancel the wave.
• Treating coral quarrying as disqualifying option (b) — the option states a use, and the use is real.

A NOT item that rewards asking what physical hazard each option names, rather than which options sound environmentally positive.

• practice — not a real PYQ

  Which one of the following conditions is least favourable to the growth of reef-building corals?

  • (a)Warm water above about 20 degrees Celsius
  • (b)Clear, sediment-free water
  • (c)A large inflow of fresh river water
  • (d)Shallow water within the reach of sunlight

  Answer(c) A large inflow of fresh river water — it lowers salinity and carries silt that smothers the polyps, which is why reefs are absent at large river mouths.

• practice — not a real PYQ

  Coral bleaching is best described as which one of the following?

  • (a)The death of the coral skeleton by dissolution
  • (b)The expulsion of symbiotic algae from the coral polyps
  • (c)The deposition of white sediment over a reef
  • (d)The migration of reef fish away from the reef

  Answer(b) The expulsion of symbiotic algae from the coral polyps — losing the algae removes the colony's colour and its main food supply.