Pelagic:
Any water in a sea or lake that is neither close to the bottom nor near the shore can be said to be in the pelagic zone. The word “pelagic” is derived from Greek πέλαγος (pélagos), meaning ‘open sea’. The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes from the surface of the sea almost to the bottom. Conditions differ deeper in the water column such that as pressure increases with depth, the temperature drops and less light penetrates. Depending on the depth, the water column, rather like the Earth’s atmosphere, may be divided into different layers.
The pelagic zone occupies 1,330 million km3 (320 million mi3) with a mean depth of 3.68 km (2.29 mi) and maximum depth of 11 km (6.8 mi). [Wikipedia]
Noted in “Quantification of bioluminescence from the surface to the deep sea demonstrates its predominance as an ecological trait,” Séverine Martini & Steven H. D. Haddock, Scientific Reports:
For coastal environments less than 2.5% of the species are estimated to be bioluminescent15, while for pelagic environments, this percentage is considerably higher. Indeed, the earliest studies estimate that bioluminescence occurs in approximately 70% of fish species16, and by number of individuals, 90% of fishes observed below 500 m depth in the eastern North Atlantic were said to be bioluminescent16
Dr. Haddock appears to be a fine example of nominative determinism.
