Frequently Asked Questions
Why is it dark in the deepsea?
Many deepsea fishes have large eyes. Barnard's lanternfish, Symbolophorus barnardi, has huge eyes. This fish grows to 12 cm in length and has photophores along the lower sides of the body. View larger image.
The amount of light penetrating seawater depends upon many factors including the time of day, season, geographic location and the clarity of the water.
When light passes through water, it is absorbed and scattered by water molecules and particles in the water.
As water depth increases, the longer (red) wavelengths are the first to be absorbed and scattered. By about 10 m below the surface, most of the red and orange wavelengths of visible light are no longer present (view the pipefish natural light page). A source of artificial light must be used to view reds and oranges. For this reason, many divers carry a torch even during the day.
As depth increases the scattering and absorption of shorter wavelengths (yellows and greens) becomes evident. By about 150 m depth, even in the clearest water, human eyes can only see blue light.
Beyond about 800 m the human eye can detect no visible light from the surface. At these depths the only visible light is made by living organisms (more information on bioluminescence).
The eyes of some deepsea fishes are 15 to 30 times more light-sensitive than human eyes. Some deepsea fishes can detect light in depths down to 1300 m.
Related links
- More information on lanternfish research.
- View a map of the collecting localities of Barnard's lanternfish specimens in the Australian Museum Fish Collection.
Further reading
- Helfman, G.S., Collette, B.B. & D.E. Facey. 1997. The Diversity of Fishes. Blackwell Science. Pp. 528.
- Lucas, J & P. Critch. 1974. Life in the Oceans. Thames and Hudson. Pp. 216.
