Correct Option
Net primary productivity (NPP) refers to the rate at which producers generate biomass that is available to consumers. The correct sequence of ecosystems in decreasing order of productivity is:
- Mangroves: These ecosystems exhibit very high NPP due to their location in nutrient-rich estuarine environments, high light availability, and efficient nutrient cycling. They support dense vegetation and diverse fauna.
- Grasslands: Possess moderate NPP, which is influenced by factors such as rainfall, soil fertility, and grazing pressure. They are characterized by herbaceous vegetation.
- Lakes: Generally have lower NPP compared to terrestrial ecosystems like grasslands. Productivity in lakes is often limited by nutrient availability (e.g., phosphorus), light penetration, and water depth.
- Oceans: Despite their vastness, oceans have the lowest average NPP per unit area. Open ocean regions, which constitute the majority of the marine environment, are often nutrient-poor, particularly in essential elements like nitrogen, phosphorus, and iron, limiting phytoplankton growth.
Incorrect Options
Options A, B, and D present incorrect sequences by misplacing ecosystems in terms of their relative productivity. For instance, they incorrectly rank oceans or lakes higher than their actual position in the decreasing productivity order, or disrupt the established hierarchy of productivity among these ecosystems.