The Impact of artificial light on Arctic pelagic communities during the polar night How to reduce impacts by modifying color, intensity and flashing frequency

Abstract

An increasing anthropogenic stressor in marine ecosystems is artificial light at night. Especially in the Arctic where exposure is increased by extended periods of darkness during the polar night. This study focuses on underwater artificial light used in occasional situations such as scientific sampling and measuring, stock assessment or lights from navigating boats. This study examines the effects of varying artificial light wavelengths, intensities and flashing frequency on Arctic pelagic communities, mainly fish and zooplankton, throughout the polar night. Horizontal avoidance or attraction response of pelagic organisms to an underwater artificial light source were measured using active acoustics (WBAT) during three arctic excursions (2022 to 2024). This study aims for arctic marine activities to minimize ecological disturbance during susceptible times of the year. According to the results, red light at 660 nm significantly increased avoidance behaviour, whereas red light at 720 nm increased attraction. Aurora-like and Bioluminescence wavelengths as well as green light at 525 nm produced minimal responses. Despite discernible patterns in intensity and flashing frequency fluctuations, such as greater avoidance at high flashing frequency or extreme intensities, these effects were not statistically significant due to high variability in the data. While naturalistic light spectrum can provide less disruptive alternatives, the results indicates that specific light settings such as red at 720 nm and red at 660 nm should be avoided in surveys and operational situations. This thesis contributes to developing light-use guidelines for Arctic marine activities in order to reduce ecological disturbance during the polar night.