354 



OCEANOGRAPHIC INVESTIGATIONS 



WHITE BLACK WHITE YELLOW 

 SQUARE DISK CROSS TRIANGLE 



Fig. 133. Sealab II form/color visibility range 



Bioluminescence— Bioluminescence, the production of light by living organisms, is a com- 

 mon occurrence in the marine environment. Since the advent of nighttime naval operations, 

 bioluminescence has become a problem of military significance and has received the attention 

 of a number of investigators (5, 6). Actual reports of bioluminescence however are few, and 

 for the most part consist of sightings by mariners of only exceptionally brilliant displays, of- 

 fering little in the way of quantitative or qualitative information. In 1963, Seliger, Fastie, 

 Taylor, and McElroy (7) developed a portable light-baffled underwater photometer capable of 

 measuring the bioluminescent intensities of planktonic organisms while eliminating interference 

 from ambient light. Several of these meters were made for the U.S. Navy Oceanographic Of- 

 fice, and the writers were fortunate to obtain one of these for use in Sealab 11. In operation, 

 water (with its plankton population) is drawn into a light-tight impeller housing and churned 

 rapidly, stimulating luminescent forms into light production. The output of the luminescent 

 organisms is measured by an RCA 1P21 photomultiplier tube. Measurement of the phototube 

 current is made by a transistorized dc amplifier which is included in the phototube housing. 

 Response of the amplifier is such that the integrated signal can be recorded on a Rustrak re- 

 corder. During Team 2's occupancy of Sealab, the sea unit of this instrument was attached to 

 the conning tower, and a number of night runs were made to measure the bioluminescent back- 

 ground level. Measurements made after Sept. 15 revealed that the level of bioluminescence 

 was less than the threshold detection capability of the instrument. On Sept. 15 the biolum- 

 inescent level was sufficient to cause half-scale deflection on the instrument's most sensi- 

 tive range. The effective input light level corresponding to this deflection will be determined 

 by calibration data for the instrument. 



The measurement of bioluminescent levels made with the meter correlates quite well 

 with diver observations of this phenomenon. On all night dives made between Sept. 12-15 a 

 noticeable amount of bioluminescence in the water was reported. After Sept. 15, the amount 

 of bioluminescence suspended in the water appeared to be much less. One interesting obser- 

 vation concerning the occurrence of this phenomenon at these depths is that the most intense 

 displays were restricted to a very narrow (less than 1 in.) region above any exposed surface. 

 Thus by generating a current a diver could see in detail the surface of a rock at the edge of 

 the canyon or small surface protuberances in the darkened exterior areas of Sealab. Since 

 the organisms responsible for these displays remained near or attached to the surface of these 

 objects, they could not be pumped in and detected by the bioluminescencence meter. Copepods 

 and euphasids appeared to be the primary producers of bioluminescence at these depths. 



