One-year high-frequency environmental and behavioral data from ALAN experience in a French coastal area.

Despite the widespread exposure to artificial light at night (ALAN) on coastal ecosystems, its effects are poorly studied, and data remain scarce compared to terrestrial ecosystems. Coastal areas are critical for ecosystem services, providing biodiversity, social, and commercial benefits. To acquire high-quality data on ALAN impacts on coastal ecosystems, we conducted a one-year in situ study in the "Ile aux Oiseaux" site, part of the Arcachon Bay (France), from December 2023 to November 2024. The experimental platforms consisted of two oyster tables: one for the control condition exposed to natural light and one exposed to a skyglow ALAN intensity using underwater LEDs. The impacts of ALAN were assessed using two oyster species (Crassostrea gigas and Ostrea edulis) as sentinel organisms, recording continuously their valve behavior using high-frequency non-invasive valvometer biosensors. To characterize the local environment, the experimental platform was also equipped with multiple sensors for the long-term measurement of light irradiance and additional physical parameters (temperature, water level, salinity, turbidity, conductivity, and low-frequency sound).