A new tool for monitoring ecosystem dynamics in coastal environments: Long-term use and servicing requirements of the commercial underwater bioluminescence assessment tool (U-BAT)

Abstract

The Underwater Bioluminescence Assessment Tool (U-BAT) is a small, lightweight, platform-adaptable, bioluminescence sensor for use in coastal and open ocean environments. As part of the Office of Naval Research sponsored Small-business Technology Transfer (STTR) program, WET Labs developed a commercially available bioluminescence sensor, evolved from the Multipurpose Bioluminescence Bathyphotometer third generation (MBBP-G3) technology developed at the University of California, Santa Barbara (UCSB). UBAT provides a scalable, reliable, and accurate measure of mechanically stimulated bioluminescence potential in units of photons Γ1 capable of measuring less than 1 m fine-scale vertical resolution. The objectives of this work are: 1) to highlight the importance of long-term bioluminescence measurements and show that bioluminescence, in conjunction with other inherent optical properties (IOPs) can provide a more complete picture of spatial and temporal variability of biogeochemical complexity of coastal and ocean ecosystems, and 2) to provide the potential user with general knowledge of the effect of biofouling on the measurement of bioluminescence and 3) to describe general maintenance and service requirements necessary to maintain bioluminescence data quality over long deployment periods. A commercial UBAT prototype built by WET Labs, Inc., has been deployed since 2007 on an autonomous profiling system located at the California Polytechnic State University (Cal Poly) research facility in Avila Beach, CA. The pier is an excellent test facility and is constructed of concrete and steel and extends over 1 km into San Luis Obispo Bay. The pier is 10 meters above the water where the depth of the water is 12–14 m. Sea water quality is high and provides a rich biota for research. This region is well known for its dynamic seasonal bioluminescence community which is composed of both bioluminescent Zooplankton and phytoplankton species. Vertical profiles of bioluminescence were collected every half hour along with chlorophyll fluorescence, turbidity, beam-C, conductivity, temperature, and salinity measurements. Over the deployment period, intense blooms of bioluminescence were observed and at times bioluminescence was inversely correlated with chlorophyll fluorescence and turbidity. Thus, bioluminescence, in conjunction with other IOPs, can provide a more complete picture of spatial and temporal variability of biogeochemical complexity of coastal and ocean ecosystems, particularly for the response of the planktonic community to environmental fluctuations. By broadening the use of bioluminescence measurements the UBAT will significantly increase general understanding of the roles of bioluminescence in oceanic biodynamics. Long-term deployments necessary for ecosystem monitoring require frequent system maintenance to ensure high-quality data. Prior to leaving the factory, UBAT bioluminescence light detection system and flow rate are calibrated with NIST traceable standards. Over a deployment period, increased bio-fouling typically decreases the signal accuracy. To track changes in the quality of measured bioluminescence, a validation light source is provided with each UBAT that is powered and controlled by the UBAT. The effect of biofouling on the quality of measured bioluminescence and flow rate are compared for two UBATs deployed in coastal regions, under different deployment regimes. In Avila Beach, CA, UBAT is deployed on an autonomous profiler package that is maintained outside of the water and automatically rinsed with fresh water between profiles which reduces biological growth on the sensors and the effect of biofouling on the data quality. In Yaquina Bay, OR, UBAT is deployed at a WET Labs test facility and maintained in the water during a period of peak biological growth. Yaquina Bay is a small drowned river estuary draining a 658 square km watershed located along the central Oregon coast that is very productive and also has dynamic seasonal periods for biological growth. Design changes applied to the UBAT in Yaquina Bay, OR, compared to the earlier model at Avila Beach, CA are intended to reduce the effect of biofouling. The composition of the material used for the detection chamber walls is the primary difference between the UBATs. The detection chamber of the UBAT deployed in Avila Beach, CA is composed of virgin Teflon, whereas the UBAT deployed in Yaquina Bay, OR is molded polyurethane loaded with 20% titanium dioxide. We expect that the titanium dioxide has improved anti-biofouling properties. A secondary design change was to the light baffle at the sensor exhaust. The exhaust baffle of the UBAT deployed in Avila Beach, CA is more restricted whereas the exhaust baffle of the UBAT deployed in Yaquina Bay has a 3-turn helical baffled with a copper exhaust cover. Recommendations for the frequency and method of maintenance, techniques to improve data quality and analysis of the employed anti-biofouling techniques will be discussed.