Quantitative Records of the Luminescent Flashing of Oceanic Animals at Great Depths 1

The bathyphotometer described previously and capable of responding to illumination as low as 10 −7 µ w/cm 2 has been modified in respect to circuit, housing, and cable, so that measurements of underwater light could be undertaken at greater depths. Graphical records were obtained of the intensity, duration, and frequency of flashes of luminescent animals at stations in the slope water SE of New York at depths as great as 3750 m (about 2⅓ miles). During the night flashes were recorded from 50 m downward and reached their greatest frequency of over 160 per minute at 100 m, with a secondary maximum of about 90 flashes per minute at 900 m. During the day flashes appeared above the background light penetrating from the surface beginning at about 400 m and increased in frequency with depth to over 110 per minute at 900 m. The brightest flashes were more than 100,000 times the dark level of the instrument. Flashes ranged from less than 0.2 sec to more than 1 sec in duration, with light from overlapping flashes lasting sometimes for more than 10 sec. Tests with animals in the laboratory indicated that the flashes recorded at sea originated within 10 m of the photometer. The nature of the vertical distribution of animal populations, as suggested by the variation in flashing, is compared with information derived from other types of observation. The brightness and varied pattern of bioluminescence is discussed in relation to the ecology of the deep sea.