The acidification of oceans is increasing. Why is this phenomenon a cause of concern:
- 1.The growth and survival of calcareous phytoplankton will be adversely affected.
- 2.The growth and survival of coral reefs will be adversely affected.
- 3.The survival of some animals that have phytoplanktonic larvae will be adversely affected.
- 4.The cloud seeding and formation of clouds will be adversely affected.
Which of the statements given above is/are correct?
Answer & explanation
Answer: (a) 1, 2 and 3 only
Statements 1, 2 and 3 are correct, so the answer is (a). Ocean acidification lowers the carbonate available to organisms that build calcium carbonate shells and skeletons. This harms calcifying plankton, corals and the calcifying larvae of shell-building animals. Statement 4 is not an established effect: the only link to clouds runs indirectly through the sulphur gas DMS released by marine plankton, and IPCC describes that sensitivity to acidification as uncertain.
- ✓ 1. Calcifying plankton such as coccolithophores and foraminifera build calcium carbonate shells. They are among the groups considered most at risk from ocean acidification.
- ✓ 2. Corals build their skeletons from calcium carbonate. Species that build shells or skeletons this way are particularly vulnerable to acidification.
- ✓ 3. Many shell-building animals pass through a planktonic larval stage. Near-future CO2 levels are generally harmful to calcifying larvae such as mollusc veligers and sea-urchin larvae, which threatens the survival of those animals.
- ✗ 4. Acidification has no direct effect on cloud seeding or cloud formation. The only proposed route is indirect, via DMS gas from marine plankton, and IPCC states that this sensitivity to ocean acidification remains uncertain.
- ✗ (d) Option (d) includes statement 4, which rests on an uncertain, indirect feedback rather than an established impact.
- ✗ (b) Option (b) wrongly drops statements 1 and 3, even though calcifying plankton and calcifying larvae are among the most vulnerable groups.
Remember · Ocean acidification cuts carbonate availability and hurts calcifiers: corals, calcifying plankton and calcifying larvae. The DMS–cloud link is an uncertain, indirect feedback, not an established impact.
Sources
- IOC-UNESCO: Ocean acidification, a threat to marine life ↗ “Species that build shells or skeletons from calcium carbonate, such as corals, oysters, mussels and some plankton, are particularly vulnerable”
- CBD Technical Series No. 75: An updated synthesis of the impacts of ocean acidification on marine biodiversity (Ch. 4) ↗ “calcifying (carbonate producing) plankton, such as foraminifera and coccolithophores (Figure 4.1), which are among the groups considered most at risk in future ocean acidification … Increased pCO2 within the range of near-future projections is in general negative to calcifying larvae, including mollusc veligers and sea urchin echinoplutei”
- IPCC AR5 WGI, Chapter 7: Clouds and Aerosols ↗ “the sensitivity to ocean acidification and climate change remains uncertain”
Question: UPSC Civil Services (Preliminary) 2012, General Studies Paper I. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·
