Response of peracarid assemblage (Crustacea: Malacostraca) to artificial light across different urban shallow habitats

Artificial light at night (ALAN) has been revealed as an emergent stressor in the last decades. Currently, most of the coastline is globally exposed to this stressor, causing ecological alterations in many marine species and processes. In coastal habitats, diel vertical migration is a widespread behaviour whereby organisms remain in the bottom during day, and they ascend at night. ALAN has been reported to disrupt this behaviour, even in shallow waters. Since peracarids are dominant in these coastal habitats, it is mandatory to understand if their vertical migration is compromised by ALAN. To address this issue, peracarids from the water column were collected in three urban shallow habitats with different levels of human pressure: recreational marinas, breakwaters and beaches. In each habitat, sampling was conducted during daytime, night and night adding artificial light with two portables spotlights. Our results indicated that abundance, species richness, diversity, evenness and peracarid community structure varied across habitats and light treatments, but there were not differences between night and ALAN. However, at least six species showed positive or negative phototaxis, including the dominant species Cumella (Cumella) limicola. Our results also highlighted the plasticity of this behaviour even within the same species, which could mask the response of those migrants to ALAN and thus, underestimate its impact in the assemblage. Given the important role of peracarids in shallow ecosystems, our study may help in light pollution management, especially given the increasing lighting in coastal areas.