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

The productivity of an ecosystem refers to the rate at which energy is converted into biomass per unit area per unit time. Here is the correct sequence:

Mangroves: Mangrove forests are highly productive ecosystems due to their nutrient-rich environment, high plant biomass, and rapid recycling of nutrients. They have a net primary productivity of about 2500 gC/m²/yr.

Grasslands: Grasslands have a high net primary productivity, ranging from 600 to 3000 gC/m²/yr, depending on the climate and grassland type (e.g., temperate or tropical).

Lakes: The productivity of lakes varies greatly depending on their nutrient content, size, and depth. On average, lakes have a net primary productivity of about 100-1500 gC/m²/yr.

Oceans: Although oceans cover a vast area, they have a relatively low net primary productivity due to the limited availability of nutrients in many regions. The average oceanic net primary productivity is about 125 gC/m²/yr, but it can be much higher in coastal areas and upwelling zones.