Riverine fish density, predator–prey interactions, and their relationships with artificial light at night

Urban stressors: Interactive effects of noise, light regime and fluoxetine on zebrafish behavior

Chemical, noise and light pollution are pervasive anthropogenic stressors. These stressors have been investigated individually; however, to our knowledge no one has investigated interactions between the three or their impacts on fish. The current study investigated the effects of chronic exposure to a common environmental pollutant, fluoxetine (3 and 300 ng/L), light pollution (artificial light at night), and acute environmental noise (motorboat engine) on the behavioral responses of zebrafish (Danio rerio). The effects of these treatments on zebrafish boldness, anxiety, time to feed, habitat preference in the presence of a visual predation cue (bird), and shoaling behavior in the presence of a conspecific alarm chemical and a visual predation cue were measured. Fluoxetine alone decreased zebrafish boldness, although effects were dose-, sex-, and noise-order-dependent. Zebrafish exposed to artificial light at night showed higher activity levels and were bolder than fish that were raised in an environment with a normal 12 h light-12 h dark photoperiod. Noise exposure often resulted in increased activity. However, we also observed interactions between the three factors. In several experiments, fluoxetine suppressed the effects artificial light at night, suggesting an antagonistic interaction. Fluoxetine also reduced behavioral responses to sudden noise in several experiments. The visual predation cue caused significant reductions in activity, but all three factors affected responses to predation, leading to behaviors that may increase zebrafish vulnerability. The order in which fish were exposed to noise pollution was also important. Fish that were tested with noise first often reacted more strongly than those that were initially tested without noise, suggesting that noise increased the stress of adaption to a new environment. Environmental stressors often co-exist in the real world and the limited number of studies in this area underscores the need for more comprehensive research.

LED streetlight characteristics alter the functional composition of ground-dwelling invertebrates

Artificial Light at Night (ALAN) has been identified as a primary driver of environmental change in the 21st century with key impacts on ecosystems. At the same time, developments of LED lighting systems with adjustable parameters-such as color temperature and light intensity-may provide an opportunity to mitigate the negative effects of ALAN. To test the potential effects of LED properties, we conducted a comprehensive field study over two summers at three forest sites in Switzerland. We investigated the impact of three key attributes of LED lights (color temperature, brightness, and luminaire shape) on the abundance and community structure of ground-dwelling invertebrate functional groups (predators, omnivores, and detritivores). We found a significantly increased nocturnal attraction of omnivores (+275%) and predators (+70%), but not detritivores, to ALAN, altering arthropod community composition and trophic interactions in forests. LED color temperature and luminaire shape showed minimal effects on all three functional groups, while reducing light level from 100% to 50% attracted fewer individuals in all groups with a significant effect in omnivores (-57%). In addition, we observed significant interactions of color temperatures and luminaire shapes with light intensity, with a decrease in numbers when dimming the light to 50% intensity combined with a color temperature of 3700 K for predators (-53%), with diffusing luminaire shapes for omnivores (-77%) and with standard luminaire shape for detritivores (-27%). The predator-detritivore ratio showed a significant color temperature - light level interaction, with increased numbers of predators around streetlights with 3700 K and 100% intensity, resulting in an elevated top-down pressure on detritivores. These results suggest the importance of considering combined light characteristics in future outdoor lighting designs.

Multiple environmental stressors affect predation pressure in a tropical freshwater system

Environmental change can alter predator-prey dynamics. However, studying predators in the context of co-occurring environmental stressors remains rare, especially under field conditions. Using in situ filming, we examined how multiple stressors, including temperature and turbidity, impact the distribution and behaviour of wild fish predators of Trinidadian guppies (Poecilia reticulata). The measured environmental variables accounted for 17.6% of variance in predator species composition. While predator species differed in their associations with environmental variables, the overall prevalence of predators was greatest in slow flowing, deeper, warmer and less turbid habitats. Moreover, these warmer and less turbid habitats were associated with earlier visits to the prey stimulus by predators, and more frequent predator visits and attacks. Our findings highlight the need to consider ecological complexity, such as co-occurring stressors, to better understand how environmental change affects predator-prey interactions.

Effects of anthropogenic light on species and ecosystems

Anthropogenic light is ubiquitous in areas where humans are present and is showing a progressive increase worldwide. This has far-reaching consequences for most species and their ecosystems. The effects of anthropogenic light on natural ecosystems are highly variable and complex. Many species suffer from adverse effects and often respond in a highly specific manner. Ostensibly surveyable effects such as attraction and deterrence become complicated because these can depend on the type of behavior and specific locations. Here, we considered how solutions and new technologies could reduce the adverse effects of anthropogenic light. A simple solution to reducing and mitigating the ecological effects of anthropogenic light seems unattainable, because frugal lighting practices and turning off lights may be necessary to eliminate them.