Which is the most stable ecosystem?

1. A

   Marine (ocean)

   (a) Official key: The marine (ocean) ecosystem is keyed as the most stable. Oceans have huge water volume, buffered chemistry and long food webs, which textbooks treat as high stability. Among ocean, forest, mountain and desert, the stored most-stable system is marine.

2. B

   Forest

   Forest ecosystems are productive and diverse but more disturbance-prone (fire, felling, pests) than the keyed ocean. Forest is not the official most-stable choice.

3. C

   Mountain

   Mountain ecosystems are steep, climate-zoned and erosion-prone. They are not keyed as most stable.

4. D

   Desert

   Deserts have low biomass and sharp temperature swings. They are not the stored most-stable system.

Summary. Official key is (a). Most stable ecosystem in this paper is the marine ocean. Forest, mountain and desert are less buffered in the textbook stability ranking used here. Keep ocean. The official letter is (a).