In the given options, the correct answer is option 2 - Saltwater Ecosystem. The benthic zone refers to the bottom or floor of a body of water, such as an ocean, sea, lake, or river. It is the lowest level of the water column, extending from the shoreline to the deepest parts of the water. The benthic zone is inhabited by a variety of organisms, including invertebrates, bacteria, and fish species.

Option 1 - Freshwater ecosystems also have a benthic zone, but the question specifically asks about a particular ecosystem.

Option 3 - Tundra ecosystems refer to cold and treeless regions and do not have a benthic zone.

Option 4 - Forest ecosystems refer to land areas with a dense concentration of trees and do not have a benthic zone.

Therefore, the benthic zone is found in saltwater ecosystems.