Quantifying exposure and community response to artificial light at night on temperate reefsNovel Approaches

Stephen Swearer¹, Huw Lewi-Smith², Dean Chamberlain²

¹University of Western Australia, Australia - ²University of Melbourne, Australia

Although artificial light at night (ALAN) is increasingly recognised to disrupt various physiological and ecological processes in terrestrial ecosystems, its extent and impact in temperate coastal marine environments remains poorly understood. Here we investigate how point-source ALAN and artificial skyglow influence nocturnal illumination subtidally and assess the response of fish and plankton communities. 14 pier surveys were conducted in Port Phillip Bay, Australia to assess how pier lighting influences marine ALAN exposure at the surface and across depth. To determine if artificial skyglow obscures natural cycles in moonlight, we recorded nocturnal illumination at 3 subtidal reefs over a lunar cycle. Fish species diversity and plankton abundance were recorded across lit and unlit pier sites with surface surveys, IR camera deployments, and plankton pump samples. Pier lighting intensity was up to 430 times brighter than natural full moonlight (0.3 lx). While full moon illumination was not obscured by artificial skyglow, skyglow accounted for between 10-50% of peak moonlight at depths of 2.75m. At lit sights, surface-dwelling pelagic fish were 93% more likely to be present and medium-sized plankton were 4.26 times more abundant compared to unlit sites. This indicates that pier lighting can induce unnatural attraction behaviours across marine communities and disrupt natural predator-prey dynamics. This study is the among the first to detect community-level effects of ALAN on temperate marine communities and to document subtidal temperate reefs are exposed to significant levels of artificial skyglow.