The portion of a body of water where sunlight does not penetrate is a significant ecological division. This region is characterized by a lack of light sufficient for photosynthesis to occur. As an example, in a deep ocean environment, this zone starts at the depth where less than 1% of sunlight remains. Its boundaries are determined by light penetration, not necessarily by a fixed depth.
This lightless environment is crucial to the distribution and adaptation of organisms. Many unique species have evolved to thrive in perpetual darkness, relying on alternative energy sources such as chemosynthesis or organic matter sinking from upper layers. Understanding this zone helps to comprehend the global carbon cycle and the interconnectedness of marine ecosystems. Its study provides insights into evolutionary processes and the limits of life on Earth. Historically, exploration of this realm was hindered by technological limitations, but advancements in submersible technology have expanded knowledge of its inhabitants and processes.
