Ecosystem productivity refers to the rate at which biomass is generated. Mangrove forests, with their high nutrient availability from land runoff and rich soil, exhibit very high net primary productivity. Grasslands also have significant productivity, especially during their growing seasons. Lakes can vary, but generally have lower productivity than terrestrial or coastal systems due to nutrient limitations or depth. Oceans, covering vast areas, have a lower average productivity per unit area compared to the other ecosystems listed, despite their immense total biomass.