In Nature‘s Scientific Reports, Martini & Haddock report on the observations of bioluminescence in the ocean:
Credit: NOAA/National Ocean Service
Bioluminescent and likely bioluminescent organisms were dominant in the entire water column (in blue, Fig. 2b), ranging between 48 and 77% of the organisms observed. The non-bioluminescent and unlikely bioluminescent organisms represented a small portion of the observations (in dark grey, Fig. 2b), ranging between 2 and 35%. These numbers do not total 100% due to animals undefined for bioluminescence, accounting for between 2 and 43% of the observations. Raw numbers of observations in each depth bin were normalized using the amount of time spent at each depth. As might be expected, the upper part of the water column has a lower percentage of undefined organisms than the less known deeper waters. However, when omitting the undefined organisms, in the global data set, probably bioluminescent organisms accounted for 76% of all observations (down, Fig. 2b), and the probably non-bioluminescent reached 24%. The variability of these percentages over depth is low, and the variability due to undefined organisms is also relatively constant. Indeed, the percentage varies only a small amount, from a low of 69%, if all undefined animals are assumed to be non-luminous, to 78% if they are all assigned as bioluminescent.
Given that generating light must take up some resources, it provokes thought on the utility of light to the general organism. It would certainly be interesting to partition the pelagic organisms by food source and see if bioluminescence distributions of the partitions mimic the general distribution, or if food source correlates with ability (or even choice!) to luminesce.
