Future Directions in Bioluminescence Research

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ABSTRACT

Bioluminescence Survey Systems

Mark Geiger

Naval Oceanographic Office

During the last 20 years, the Naval Oceanographic Office (NAVOCEANO) Laboratory Branch has developed a comprehensive program to routinely monitor bioluminescence activity and other environmental parameters for correlative purposes. This effort is a result of close cooperation between Navy R&D laboratories, academia, and NAVOCEANO.

The mix of theoretical and applied expertise, from concept to equipment transition, has produced reliable, versatile, and calibrated photometers to measure bioluminescence in the sea on a routine basis. The NAVOCEANO bioluminescence instrumentation suite consists of a surface mapping system, a vertical profiler, and a variable depth towed instrument.

BIOLITE Photometer System

BIOLITE, an underway photometer sensor, continuously measures bioluminescence in surface waters. This photometer was designed as a vertical profiler and built in 1981 by the Naval Research & Development Laboratory (NRaD) in San Diego. NAVOCEANO modified the instrument to allow installation in the engine rooms of its survey ships. Originally a complex, labor-intensive, roll-on/roll-off system, user-friendly improvements now allow operation by shipboard electronic technicians. NAVOCEANO's new
T-AGS-60 class ships have been designed to place the BIOLITE photometer in the bow of the ship. This forward position will reduce the amount of organism prestimulation and provide more accurate measurements of the bioluminescence potential.
BIOLITE is mounted between a modified sea chest and a pump. As seawater flows through the sample chamber, turbulence stimulates the plankton to luminesce. The chamber is viewed by four symmetrically mounted photomultiplier tubes (PMTs) that count the photons of light emitted. Water is then pumped to ancillary sensors, which include a conductivity cell, thermometer and a fluorometer. System modifications are in progress to add spectral measurements of transmission and absorption. System has built in expandability for other instruments as needed. BIOLITE will operate continuously on all NAVOCEANO ships and over the years will contribute significantly to our knowledge of the spatial and temporal variability of bioluminescence in the surface waters of the world.

HIDEX photometer system

The HIDEX (High Intake Defined EXcitation) photometer is a vertical profiler designed and built at the University of California at Santa Barbara with funding from the Naval Research Laboratory's Tactical Oceanographic Warfare Support office. HIDEX was built to remedy problems highlighted by previous photometer designs. The high intake flow (up to 35 liters/sec) significantly improves sampling statistics. The high flow also reduces population sampling bias by capturing faster swimming organisms, which were able to avoid capture in low flow-rate photometers.
An additional benefit of the high intake is the faster profile rate; 200-meter HIDEX profiles typically require less than 20 minutes to complete. The defined excitation of organisms means that the turbulence is hydrodynamically characterized and prestimulation of the organisms is kept to a minimum. The 130-centimeter-long sample chamber provides residence times of sufficient duration to measure the entire flash of an organism. Fiber optics views the entire chamber volume to measure the total stimulable light of the population. A ring of fibers, near the intake, views a narrow cross-section of the chamber to monitor the number of bioluminescent events or flashes. Finally, eight PMTs view equal cross-sectional volumes along the length of the chamber to determine population flash kinetics. Together, these light measurements help to characterize the responsible bioluminescent organisms. Environmental instrumentation includes conductivity, temperature, depth, a 1-meter path-length blue transmissometer, a 25-centimeter pathlength transmissometer and in situ fluorometer.

TOWDEX photometer

The TOWDEX (TOWed Defined EXcitation) photometer combines the horizontal coverage of BIOLITE with the vertical capabilities of HIDEX. All of the basic HIDEX features are duplicated but are packaged in a body for towing at speeds to 10 knots. Depth is controlled by computer-operated movable wings; the operator can input a single tow depth or a minimum and maximum depth [including the period and number of cycles (TOW-YO)] or fly manually. The port and starboard wings move independently to control roll. An auxiliary instrument bay in the belly of the tow body contains an in situ fluorometer and a 25-centimeter path-length transmissometer, an ac-9 spectral absorption attenuation meter, a thermometer, a conductivity cell, a dissolved oxygen sensor, and a pH sensor. All data are sampled at 0.5-second intervals and merged with global positioning system (GPS) information into ASCII files for data analysis and presentation. These data give a comprehensive record of bioluminescence in a region.

All of the photometers are radiometrically calibrated on an annual basis, and empirical field-testing has demonstrated data comparability of all photometer types. The NAVOCEANO Laboratory Branch continues to interface with other Navy Organizations and academia to expand and improve our bioluminescence survey capability and to incorporate other sources of data into a relational database.

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