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An ecosystem is made up of all species and their interactions with their physical living environment. As a result, both biotic and abiotic animals coexist in an ecosystem.

Due to their enhanced exposure to the tidal flow, salt marshes have high net productivity. Asof their primary production, salt marshes contribute to food chains in wetlands and neighboring marine ecosystems.

Thus, salt marshes do not have the lowest net primary productivity.

Therefore, the given option is incorrect.

The net primary productivity of open oceans is 50鈥�1200 per meter square area. This productivity is the lowest in all the coastal zones. Most primary productivity of the ocean is carried out by free-floating phytoplankton.

Thus, open oceans have the lowest net primary productivity.

Therefore, the given option is correct.

Coral reefs grow in warm, shallow waters with a strong current. Corals are colonial organisms with photosynthetic algae in their cells. The coral reef's net primary productivity is 2000 per meter square.

Thus, the net primary productivity of coral reefs is not the lowest.

Therefore, the given option is incorrect.

Water, sunlight, and high temperatures are constant in tropical rainforests, and there is a dense population of plants, resulting in a very high GPP and net primary productivity. As a result, increased productivity boosts biomass.

Thus, tropical rainforests do not have the lowest net productivity.

Therefore, the given option is incorrect.