Correct Option: D

Productivity is the rate of organic matter or biomass production. The average ocean productivity is about 50 grams carbon per square meter per year; while, the average land productivity is 160 grams carbon per square meter per year. Salt marshes and mangroves have one of the highest productivity of 3300-6000 grams carbon per square meter per year. So the correct sequence of ecosystem in the order decreasing productivity is: Mangroves > Grasslands > Lakes > Oceans.