What is a gray habitat and what do they need to survive?

Grey habitats, also called "marginal habitats", are environments capable of supporting life but offering a minimal number of resources and nutrients. It is in these habitats that extremophiles, microorganisms adapted to extreme conditions, reside.

Due to their lack of resources, grey habitats are considered transitional sites, where microorganisms temporarily reside while adapting to more favorable environments, or permanently, if they possess adaptations or symbiosis that allow them to survive in the limited resource environment. For example:

- Some grey habitats are only available for short periods, becoming inhospitable the rest of the year. This is the case of ponds or puddles that dry up in summer.

- Other habitats provide enough nutrients for organisms to survive permanently, but with such restrictions that populations are extremely small. Acidic ponds, or highly saline lagoons, are habitats where few organisms can thrive, but those who can are so well-adapted that they don't need to move to a more favorable environment.