A multi-platform bathyphotometer for fine-scale, coastal bioluminescence research

Although bioluminescence (BL) in the open ocean has been extensively studied, coastal BL remains poorly understood due, in large degree, to a lack of BL instrumentation appropriate to measure the fine-scale biological and physical complexity of the coastal regime. As a contribution toward understanding coastal BL, we developed the Multipurpose Bioluminescence Bathyphotometer (MBBP). This compact, self-contained bathyphotometer (BP) was designed to function in a variety of deployment modes, including conventional shipboard profilers, towed platforms, autonomous underwater vehicles (AUVs), and profiling moorings. In all configurations, the instrument preserves signal structure at centimeter to meter scale resolution, the scale at which higher-flow instruments might disturb thin layers and other fine-scale water column features. In the MBBP, seawater is conveyed with minimal premeasurement excitation into a light-baffled stimulation and measurement chamber at a continuously measured flow rate of 350 to 400 mL s(-1). A photomultiplier tube (PMT) records light from bioluminescent organisms after they are mechanically stimulated at the chamber entrance by a high-velocity impeller. Calibration and test protocols were developed to determine BL stimulation efficiency and MBBP measurement characteristics. To illustrate the capabilities of the MBBP to resolve the fine-scale structure of the BL community, measurements from two coastal environments are presented.