Light pollution affects the behavior and life history traits of aquatic invertebrates

Circadian rhythms regulate essential biological processes, including behavior, reproduction and survival, across diverse organisms. Disruptions to this cycle, whether through artificial light at night (ALAN) or reduced exposure to full-spectrum daylight, can interfere with biological processes and ultimately threaten biodiversity. This concern is growing as ALAN spreads beyond urban areas through streetlights and skyglow. Aquatic ecosystems, in which zooplankton play a key role as primary consumers as well as prey for higher trophic levels, are particularly vulnerable. Despite growing research on the impact of ALAN on some zooplankton, rotifers remain largely understudied. Here, we conducted two experiments to assess the effects of light on Brachionus species. The first experiment examined how different ALAN wavelengths influenced life history traits in three Brachionus species, while the second one investigated the attachment behavior of B. rubens on a Daphnia host under four light conditions. Our findings reveal that ALAN has strong but species-specific effects on rotifers. Green light enhanced survival and reproductive output in B. calyciflorus sensu stricto, while suppressed reproduction in B. fernandoi. In B. rubens, white light particularly altered reproductive patterns and attachment behavior. These results highlight the complex and species-specific impacts that ALAN has on rotifers, emphasizing the need for further research to fully understand its broader ecological consequences.