Bioluminescence, a remarkably widespread phenomenon in all regions and depths of the sea, is the only light in the huge volume of the seas below the depth of astronomical light penetration. The MSI research group headed by James Case has worked for many years on this phenomenon. Recently, with support of the Office of Naval Research, they developed a new detector, shown above, for marine bioluminescence. Unlike their previous instruments, this bathyphotometer was a challenge to design and construct because it had to be quite small because its ultimate use is in an autonomous underwater vehicle (AUV) only 7 inches in diameter and about 4 feet long.

The illustration shows a highly magnified view of two cells of the marine dinoflagellate Pyrocystis fusiformis, which produce brilliant flashes of light when mechanically stimulated, and which, sometimes occurring in huge numbers, is one of the well-known red tide organisms. The bathyphotometer is shown opened up on its underwater test frame. Water is pumped into the device at high velocity and the resulting excited bioluminescence is measured with a photomultiplier. To the right in the figure is shown the display of data showing bioluminescence in yellow plotted against depth along with other data such as temperature turbidity and fluorescence. In the configuration shown the instrument was deployed in a first field test as a vertical profiling instrument during the recent Thin Layers study in Puget Sound. There, in collaboration with zooplankton expert Alice Alldredge and ocean acoustician Van Holliday, the first good correlation of acoustic plankton detection with bioluminescence were obtained.

Later this year integration with an AUV will be made and free field tests conducted in collaboration with the Woods Hole Oceanographic Institution. While the device has many pure science applications, both as an independent instrument or as part of the instrumentation load of an AUV, it is anticipated that the Navy will use such instruments in survey work to assess environmental risks in advance of naval coastal operations.