Future Directions in Bioluminescence Research

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UNCLASSIFIED WORKGROUP SESSIONS

New Sensors and Technology
Discussion Leader: Casey Moore

The discussion on new sensors presumed from the onset that researchers needed a generation of tools that provided a means of making widespread common bioluminescence measurements. In addressing Navy needs for developing predictive capabilities that can assess regional and local bioluminescence activity, the workgroup rapidly developed a consensus that making more measurements of bioluminescence was necessary. Good predictive models rely upon abundant real data and there is a paucity of the latter presently available to the general scientific community. There are relatively few sensors and platforms in operation, and the availability of data is limited. Moreover, the lack of inter-calibration information for these platforms further complicates the use of the available data.

The workgroup reviewed the suite of sensors presently available to the community to determine whether any of these instruments or systems might serve as a prototypical starting point for developing a next generation commercial sensor. Conversely it was hoped that by looking at what we have, we might close upon a more concise definition of what we might need. The table below provides a summary of these sensors, and their presently perceived strengths and limitations.

Sensor	Description	No. in existence	Strengths	Limitations
Biolight Color	NAVO shipboard underway sampling photometer system	8	Simple, robust,	Surface sampling only Lower volume sampling
HIDEX TOWDEX MOORDEX	UCSB developed family of sensors for dual use biological and photic assessment of bioluminescent organisms	6	Provide high volume sampling, kinetic information, Effective standard for other measurements	Large, high cost, high power. Heavy spatial mixing of water column
OFF-the Shelf HIDEX derivative	HBOI developed derivative of HIDEX for near shore operations	prototype	Provides HIDEX level assay, with lower cost components	Still big, and power hungry and expensive
BPR	UCSB developed REMUS deployable bathyphotometer	prototype	Much smaller, AUV capable	Lower volume sampling.
Glowtracka	Chelsea Instruments commercial bathyphotometer for towed operations	<10	Commercially available	Relatively high cost, limited volume sampling, unknown to U.S. scientists
SPD/XPB	Expendable free fall bathyphotometer	prototype	Potential low cost, simple technology, low power	Unknown sensitivity, calibration maybe difficult, night-time use only.
SPLAT	Large screen imaging bathyphotometer system for moving vehicles and free fall profilers (see Widder abstract)	prototypes	Powerful taxonomic potential, no pump! Potential high spatial resolution	Platform specific, night-time use only, potential low power.

The summarized sensors encompass a variety of designs and sampling methods for obtaining bioluminescence information. These disparate approaches included imaging receivers versus radiometric receivers, pumped excitation versus intrinsic motion excitation, and expendable sensors versus permanent systems. Moreover there exists numerous possibilities for alternative approaches, including water volume capture chambers, acoustic excitation probes, AUV, AUV stimulators combined with UAV and AUV receivers, and possible alternative sensors to provide proxy measurements that might be correlated with the bioluminescence light field.

While each of these sensors and methods provide potentially valuable information, no single solution provided a complete solution. The question then becomes exactly what the minimum criteria might be for a commercially available sensor. The summary points of this part of the discussion were:

• The sensor should not attempt to sample all bioluminescent organisms within the water, but rather should be optimized for dinoflagellate detection. Dinoflagellates are only one of many potentially bioluminescent groups of organisms living within the ocean, and biasing the sensor this way will certainly result in some inaccuracies. On the other hand dinoflagellates are the most ubiquitous emitters and form the dominant bioluminescent groups within most locales. Sampling for dinoflagellates only lifts major constraints from any envisioned commercial sensor in that these organisms tend to aggregate and do not engage in avoidance behavior from a pumped intake. A sensor designed for dinoflagellate sampling might also fit well with initial ecologically based modeling efforts that might only focus on this one group as opposed all bioluminescent plankton.
  
  
• The sensor should provide a known, quantifiable excitation and accommodate a standard and meaningful radiometric receiver calibration. In collecting a meaningful data base of real world data it’s imperative that signals collected by sensors must hold some calibration that allows scientists to correlate data collected by different sensors in different places at different times. This dictates the need for a meaningful calibration.
  
  
• The sensor or sensors must be mass producible and made available to the Navy and the scientific community at a low cost. Accumulating large numbers of measurements requires large numbers of sensors on a variety of platforms. Short of a major programmatic effort to place sensors into a number of scientists’ and Naval personnel’s hands, the best solution for accomplishing this goal likely involves producing a sensor that is of low enough cost to make it a discretionary budget component for a given researcher.
  
  
• The sensor should easily integrate with other sensor suites and sampling platforms. Design efforts need to focus upon making package size, power consumption, and data interfaces compatible with various deployments and platforms.
  
  
• The sensor should be able to sample on spatial and temporal scales compatible with other commercially available physical, chemical and bio-optical sensors. In the past 7 years advances in acoustic and optical instrumentation have provided biologists with a set of tools for measuring biological processes on the same spatial and temporal scales as physical measurements. In coastal environments this has proven especially invaluable. Biological populations coupled with high gradients in density and temperature have been shown to aggregate in concentrations that are orders of magnitude above the background. These populations are at times highly localized in layers of 5 - 50 cm and often times are grossly under-sampled or even undetected by discreet sampling techniques. Dinoflagellates are among the plankton that aggregate in these layers and it is thus highly desirable that the sensors used for the detection of their photic output operate at appropriate time-space scales to fully detect them.

We focused upon the concept of a low cost, simple, pumped bathyphotometer as a core approach for building a more generally available sensor. Depending upon specific design the pumped bathyphotometer can accommodate numerous sampling strategies and deployments, the simple configuration allows relatively low cost manufacturing, the pumped, light-baffled flow chamber provides an effective base for calibrated measurements, and when operated at lower pumping volumes the instrument can operate at low power levels.

The group also recognized the need to use and further advance alternative sensors presently, and soon to be, available. We saw the other sensors fulfilling several important needs in the overall sampling strategy.

• They will give us a calibration and validation mechanism.
  
  
• They will help fill in the sampling picture.
  
  
• They will assess the sampling limitations of the primary sensors.
  

Particular interest was shown for the SPLAT detectors under development and use by HBOI and the SPD-XBT expendables under development at WHOI.

The HIDEX series of sensors were considered the standards by which the newer technologies would get validated. Continued use of these platforms seemed imperative in order to accomplish a transition to more broadly available simple instruments.

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