Prelims 2013 · archive
MediumWhich one of the following is the correct sequence of ecosystems in the order of decreasing productivity?
Answer & explanation
Answer: (c) Mangroves, grasslands, lakes, oceans
Mangroves are among the most productive ecosystems on Earth. Grasslands come next, then lakes and streams. Oceans come last because open-ocean productivity per unit area is very low. The order is therefore mangroves, grasslands, lakes, oceans.
- ✗ (a) This reverses the order. Oceans are the least productive of the four, and mangroves are the most productive.
- ✗ (b) Oceans cannot rank second. Open-ocean productivity (about 125 g/m²/yr) is lower than that of lakes and streams (about 250) and grasslands (about 600).
- ✓ (c) Mangroves are tidal swamp forests with primary production equal to that of tropical evergreen forests and coral reefs. Swamps and marshes average about 2,000 g/m²/yr, temperate grassland about 600, lakes and streams about 250, and open ocean about 125.
- ✗ (d) Oceans are placed first, but they are the least productive. Grasslands also rank above lakes, not below them.
Remember · Productivity falls in this order: mangroves and other swamps, then grasslands, then lakes and streams, then open ocean. Oceans cover about 70% of the Earth's surface, but their productivity per unit area is low.
📘 Read it in NCERT: Class 12 Biology, Ch 12 (practise this chapter)
Sources
- NCERT Class 12 · Biology, Chapter 12 “Of this, despite occupying about 70 per cent of the surface, the productivity of the oceans are only 55 billion tons.”
- Alongi (2014), Carbon Cycling and Storage in Mangrove Forests, Annual Review of Marine Science (hosted by WHOI) ↗ · reference work “They are highly productive ecosystems with rates of primary production equal to those of tropical humid evergreen forests and coral reefs.”
- Portland State University – Biome Productivity (mean NPP, g/m²/yr, from an environmental science textbook table) ↗ · reference work “temperate grassland 600 tundra and alpine 140 desert and semidesert shrub 90 extreme desert, rock, sand, and ice 3 cultivated land 650 swamp and marsh 2000 lake and stream 250 open ocean 125”
Question: UPSC Civil Services (Preliminary) 2013, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·