Correct option is D
Explanation-
Net Primary Production (NPP) → It is the amount of organic material (biomass) produced by plants and algae after using some of it for their own respiration. It reflects how much energy is available for the next trophic levels (herbivores, carnivores, decomposers, etc.).
NPP = Gross Primary Production (GPP) – Respiration
The given ecosystems-
C. Algal beds and Coral reefs
It has extremely high productivity ~2000–2500 gC/m²/year (gram Carbon per square meter per year). But total global area covered is very small. Therefore, its total contribution to global NPP is small despite high productivity.
Example: Coral reefs are called "rainforests of the sea" due to their intense productivity but they occupy only ~0.1% of the ocean area.
D. Marshes and Swamps
The productivity is around ~2000–2500 gC/m²/year (comparable to coral reefs, sometimes even higher in freshwater marshes). Area is larger than coral reefs but still much smaller than open ocean or tropical forests. Total global contribution is moderate.
Example: Mangroves, salt marshes, freshwater swamps have rich biodiversity and high NPP.
A. Tropical Rain Forests
The productivity is ~2000–3000 gC/m²/year but very large global area (Amazon, Congo, Southeast Asia, etc.) So, it has highest global contribution to NPP.
Example: Amazon Rainforest alone contributes ~10% of global NPP.
B. Open Ocean
The productivity is very low (~125 gC/m²/year) because of nutrient limitations and covers ~70% of Earth’s surface. Despite low productivity per unit area, total global contribution is large because of its vast area.
Example: Open oceans contribute about 25–30% of the total global NPP.
Final answer - Correct option is d : C → D → A → B
