Which of the following are characteristics of Coral Reefs ?
(a) These are the oldest living communities on Earth.
(b) It is a high biomass producer.
(c) It is a rich floral and fauna diversity.
(d) Th

Question

Which of the following are characteristics of Coral Reefs ?
(a) These are the oldest living communities on Earth.
(b) It is a high biomass producer.
(c) It is a rich floral and fauna diversity.
(d) These are shallow water tropical ecosystems.
Which of the above statement/s is/are correct ?

UnlockIAS · Accepted Answer

Correct — option (4). All four statements describe properties that coral reefs are ordinarily credited with, so the row that accepts every one of them is the answer. Statement (a) calls them the oldest living communities on earth; reef-building organisms have been constructing limestone frameworks in warm shallow seas since the Palaeozoic, and a coral reef is regularly described in this way because the community, if not any particular reef, has persisted through immense stretches of geological time. Statement (b) calls the reef a high biomass producer, and that is one of its defining features: gross primary productivity on a reef is among the highest measured for any ecosystem, comparable with a tropical rain forest, and the reason is the partnership at the centre of the system, in which the coral polyp houses microscopic algae called zooxanthellae within its own tissues and receives from their photosynthesis the greater part of the food it needs. Statement (c), printed in broken English as a rich floral and fauna diversity, asserts the reef's biological richness, and the standard figure makes the point: coral reefs occupy far less than one per cent of the ocean floor and yet shelter something like a quarter of all marine species, which is why they are called the rain forests of the sea. Statement (d) calls them shallow water tropical ecosystems, and that follows directly from the partnership described above: because the zooxanthellae must photosynthesise, reef-building corals are confined to clear, sunlit water, generally shallower than about fifty metres, with temperatures between roughly twenty and thirty degrees, normal sea salinity and a firm foundation, which restricts them to the tropical belt. With no statement failing, option (4) is the answer.

Why the other options are wrong — (a) This row accepts the first two statements and drops the last two, and both of the dropped statements are sound. The richness of reef life is the property for which reefs are best known — a quarter of all marine species on a fraction of one per cent of the sea floor — and their restriction to warm, shallow, clear water is the condition that makes reef formation possible at all. Candidates arrive at a row like this by a particular route: they verify statements until they meet one they are unsure of and then stop, taking the row that covers what they have checked. In a question of this shape that is a losing method, because the rows are constructed so that every partial selection is available. Each statement has to be judged, and only then can a row be chosen.  (b) This row accepts the first, second and fourth statements and excludes only the third, the one asserting rich floral and faunal diversity. It is the most dangerous row in the question, because the exclusion looks deliberate and the statement excluded is the one printed in the worst English — a rich floral and fauna diversity is not a sentence a textbook would write, and a candidate who has been trained to distrust oddly worded options will suspect it. The wording is a defect of the printing, not of the fact. Coral reefs are among the most diverse communities in the sea, supporting fish, molluscs, crustaceans, echinoderms, sponges, turtles and algae in enormous variety, which is exactly why they are compared with tropical rain forests. Judging a statement by its grammar rather than by its content is how this row collects its victims.  (c) This row accepts only the third statement and rejects the other three, which requires a candidate to believe that reefs are neither ancient, nor highly productive, nor confined to shallow tropical water. Each of those rejections is wrong, and the last is the most clearly so, since the dependence of the coral polyp on its symbiotic algae ties reef growth to sunlight and therefore to shallow, clear water in the warm belt of the oceans; that is why the world's reefs lie in a band on either side of the equator and why the deep and the cold seas have none of this kind. The row is chosen by candidates who recognise the diversity of reefs as the one thing they are certain about and treat certainty on one point as a reason to reject everything else. Confidence in one statement is not evidence against the others.

Concept: A coral reef is built by colonies of tiny animals, the coral polyps, which secrete skeletons of calcium carbonate and grow one upon the other until a limestone framework accumulates. The reef-building or hermatypic corals live in symbiosis with single-celled algae, the zooxanthellae, which live inside the polyp's tissues, photosynthesise, and pass much of what they make to their host while using the host's waste products in return. That partnership explains almost every feature of reefs. It explains their extraordinary productivity in seas that are otherwise nutrient-poor, because nutrients are recycled within the system instead of being lost; it explains their confinement to clear, shallow, sunlit water, since the algae need light; and it explains their vulnerability, because when the water is too warm for too long the polyps expel their algae, lose both their colour and their principal food supply, and the reef bleaches and may die. The conditions reef corals require are warm water of about twenty to thirty degrees, depths generally less than fifty metres, clear water free of silt, normal salinity and a firm substrate. Reefs take three classic forms — the fringing reef attached to the shore, the barrier reef separated from it by a lagoon, and the atoll, a ring of reef enclosing a lagoon with no island in the middle — and Darwin explained the sequence by the slow subsidence of a volcanic island beneath an upward-growing reef. India's reefs lie in the Gulf of Kachchh, the Gulf of Mannar, the Lakshadweep atolls and the Andaman and Nicobar Islands.

State PCS 2022 Q17 — Environment & Ecology PYQ with Answer

State PCS 2022 Q17 — Environment & Ecology PYQ with Answer