Which of the following reasons caused catastrophic coral bleaching and mass coral deaths in the Andaman and Nicobar Islands ?

Question

UnlockIAS · Accepted Answer

Correct — B, Increase of 2° C temperature in the Indian Ocean. Mass bleaching in the Andaman and Nicobar reefs is a thermal event. Reef-building corals live in symbiosis with microscopic algae called zooxanthellae that sit inside their tissues and supply most of their food; when the water stays a couple of degrees above the normal summer maximum for even a few days, the symbiosis breaks down, the coral expels the algae, and the white calcium-carbonate skeleton shows through the now-transparent tissue. That is bleaching, and if the heat persists the colony starves and dies. The Andaman event of April–May 2010, studied by scientists of the Central Agricultural Research Institute at Port Blair with satellite data, is the textbook Indian case: the average sea-water temperature in the first week of May 2010 was about 33.8 °C against a normal of roughly 30–31 °C, and the published finding is blunt — a summer sea-surface-temperature rise of 2–3 °C above the normal maximum can kill the corals. Bleaching that season ranged from about 37 to 70 per cent of coral cover across the surveyed sites, with Havelock and South Button worst hit. A rise of the order of 2 °C is therefore exactly the stated cause.

Why the other options are wrong — (a) The Andaman and Nicobar Islands have very little coastal industry — they are a protected island territory with a small population — and industrial effluent is in any case a local, point-source stressor. It cannot explain simultaneous bleaching across reefs scattered over hundreds of kilometres of open sea, which is what a basin-wide warming episode does.  (c) Pollution, sedimentation and nutrient run-off genuinely degrade reefs and slow their recovery, so this is the most tempting wrong answer. But it damages reefs patchily and over years; it does not turn whole reef systems white in a single summer. The 2010 Andaman bleaching tracked the temperature record, not any pollution event.  (d) Cold shock can bleach corals as a physiological matter, but nothing of the kind happened here: the Andaman episodes of 1998, 2002, 2005 and 2010 were all heat events, and a 4 °C cooling of the tropical Indian Ocean is not something the observational record shows. The option inverts the actual mechanism.

Concept: Coral bleaching is the loss of the symbiotic algae (zooxanthellae) that live in coral tissue and give the coral both its colour and most of its nutrition. Heat is the dominant trigger: bleaching typically sets in when the summer sea-surface temperature maximum is exceeded by 1–2 °C and stays there for a few days, and reef scientists put the operational threshold in Indian waters at roughly 31 °C sustained for more than about three days. Bleached coral is not automatically dead — if the water cools quickly the algae can be reacquired — but prolonged heat converts bleaching into mass mortality.

State PCS 2024 Q19 — Environment & Ecology PYQ with Answer

State PCS 2024 Q19 — Environment & Ecology PYQ with Answer