Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?

1. Productivity in ecosystems typically refers to Net Primary Productivity (NPP), which is the rate at which producers (like plants or algae) accumulate biomass. 2. Mangroves are highly productive ecosystems, often comparable to tropical rainforests, due to abundant sunlight, water, and nutrient inputs from both land and sea. 3. Grasslands have moderate productivity, generally higher than lakes (on average) and open oceans, supported by grasses adapted to specific rainfall regimes. 4. Lakes exhibit variable productivity depending on nutrient levels (oligotrophic to eutrophic). On average, their productivity per unit area is lower than grasslands but higher than the open ocean. 5. Oceans, while vast and contributing significantly to global NPP in total, have very low productivity per unit area, especially in open ocean regions away from coasts and upwelling zones, due to nutrient limitations. 6. Therefore, the correct sequence of these ecosystems in order of decreasing productivity per unit area is generally: Mangroves > Grasslands > Lakes > Oceans.