* "Region of no light" is a general term. It could refer to:

* The aphotic zone: This is the part of the ocean below the photic zone (where sunlight can penetrate). It's truly dark, and life here has adapted to survive without photosynthesis.

* Caves: Some caves are completely dark, even if they're not underwater.

* Deep underground: The Earth's crust is generally devoid of light.

* "Aquatic environment" means a water-based environment.

So, is the region of no light ALWAYS aquatic? No.

Is the region of no light SOMETIMES aquatic? Yes! The aphotic zone in the ocean is an example.

To be more precise, we need to clarify what "region of no light" we're talking about.