Disrupted darkness: the impact of anthropogenic light at night on melatonin secretion of Hermodice carunculata (Polychaeta, Annelida).

Anthropogenic light at night (ALAN) can have serious impacts on marine environments. Several studies have demonstrated that ALAN disrupts melatonin production, a hormone critical for regulating circadian rhythm. In this study, the effects of ALAN on melatonin and two of its related indolamines were investigated in the annelid Hermodice carunculata. Specifically, melatonin, serotonin and tryptamine levels were measured every three hours over a 24 h period in the heads of the annelids maintained under constant light and a 12 h light/12 h dark photoperiod, representing control conditions. Melatonin concentration was quantified using an enzyme immunoassay, while serotonin and tryptamine were analyzed by liquid chromatography-tandem mass spectrometry. Melatonin levels in annelid heads remained relatively constant with a pronounced peak at 11:00. A similar pattern was observed under constant light, but the melatonin peak shifted to 14:00. However, serotonin and tryptamine did not exhibit any significant diurnal variations due to constant light exposure. These findings suggest that melatonin secretion in H. carunculata is sensitive to ALAN, whereas its related indolamines are potentially not. The disruption of H. carunculata's melatonin secretion pattern may affect its night-time behavior and reproduction, highlighting the need for further studies to assess the ecological effects of ALAN on various marine invertebrates.