Artificial light at night (ALAN) is a pervasive anthropogenic pollutant, increasing in intensity and scope. While its impacts on biological and ecological processes are well documented among terrestrial taxa, marine organisms have received less attention, though a quarter of the world's coastlines are affected by artificial light at night. Furthermore, the intergenerational effects of artificial light at night have never been documented in the wild. We conducted a field manipulation experiment in the lagoon of Mo'orea, French Polynesia, using LED (Light-Emitting Diode) lights to test artificial light at night's effects on adult life-history and offspring fitness of the coral reef anemonefish Amphiprion chrysopterus. Exposing adults and embryos to LEDs, we found artificial light at night enhanced adult growth but did not alter measured reproductive traits, including fecundity. We observed reduced parental reproductive hormone levels with downstream consequences for offspring. Hatching success was unchanged, but offspring showed reduced embryonic heart rate and yolk sac size, and drastically diminished larval escape responses and swimming performance. This comprehensive study is the first in a wild organism to demonstrate combined intergenerational and direct negative effects of artificial light at night, highlighting limited compensatory capacity. These impacts could impair larval recruitment and hinder population replenishment in reef fish. This research underscores urgent need for conservation and management to address artificial lighting impacts.
