Biosealight: A Low-Cost, Compact, Autonomous, Low-Energy, High-Sensitivity Sensor for Detecting Marine Bioluminescence

Bioluminescence, the light emitted naturally by marine organisms, is an important way of communication between organisms in the mesopelagic zone. Nearly 75% of marine organisms, from the surface to the deep sea, and accross a wide taxonomic diversity, use this capability for communication with diverse ecological goals. Bioluminescence detection thus offers an indirect way of tracking the presence of organisms (ranging from zooplankton, dinoflagellates to fishes), their distribution and diel migrations. Such detection can lead, for example, to a better understanding of auto- and heterotrophic plankton communities, vertical migrations of organisms and consequently of a better quantification of the active carbon export in the mesopelagic ocean. However, current technologies still limit large deployments, and high acquisition frequency observations of in situ bioluminescence. This publication aims to describe a new low cost, compact, autonomous, and multi-sensors instrument developed to measure in situ bioluminescence: Biosealight. The sensor's acquisition system is built around a high-sensitivity photon detector that detects photons and converts their number into proportional electrical signals. The photon detection system is integrated with additional sensors that record environmental, including pressure (rated up to 600 bar), temperature, and various system voltages. These measurements are managed by a motherboard featuring an STM32 microcontroller. This motherboard interfaces with a dedicated daughter board, which hosts voltage regulators, the pressure sensor, a high-voltage power supply (>50 V) necessary for the photon detector, amplification electronics, and data storage capabilities consisting of a 1 GB flash memory module with an optional μSD card. Biosealight detects very low light at wavelengths around 450 nm. The acquisition frequency for the bioluminescence sensor is 500 Hz. Other sensors (pressure, temperature) have an acquisition frequency of 38 Hz. High-capacity battery packs power the entire system. The sensor is designed to be easily deployable on a wide range of vectors (such as underwater gliders, CTDs, buoys, trawls...). The sensor being easy to deploy will enable to collect a wide range of bioluminescent data with high spatiotemporal resolution, while recording environmental variables related to the organisms. Various stages of specification research and test protocol under controlled conditions have led to the characterization of the sensor performance in capturing subtle bioluminescent events. It involved calibration procedures designed to verify and optimize key performance parameters such as sensor sensitivity, sampling frequency, and measurable intensity ranges. Dedicated tests were implemented to assess environmental robustness, along with marinization integration protocols, ensuring the sensor maintains operational integrity under challenging marine conditions, including long-term exposure to high pressure cycles and varying temperature. By proposing another way to measure the bioluminescence in situ, and being easy to deploy, this instrument will increase the capacity to observe and charaterize bioluminescence of organisms and improve our understanding of its ecological role.