Artificial Light at Night Disrupts Ecosystems, Even at Low Levels, Studies Find

Artificial light has made night streets safer for humans and is a convenience, but at what cost to wildlife?

Artificial light at night (ALAN) can disrupt the circadian rhythm of wild animals, interfering with sleep and migratory patterns. It can lead species like moths, sea turtles and frogs dangerously astray and make animals more vulnerable to prey.

Now, a new collection of studies on ALAN demonstrates the sweeping impacts of light pollution. Researchers found that even at low levels, ALAN can disturb communities of species, as well as entire ecosystems, a press release from the German Centre for Integrative Biodiversity Research (iDiv) said.

“From a biological perspective, natural light regimes, in contrast to other environmental conditions such as temperature, have remained more or less consistent over aeons of Earth’s history. This makes light pollution a novel perturbation to which organisms are unlikely to have evolved the ability to cope with change. Thus, it is not surprising that ALAN has the potential to fundamentally disrupt physiology and behaviour of many organisms,” the introduction to the special theme issue consisting of 16 scientific papers said.

The collection, “Light pollution in complex ecological systems,” was published in the journal Philosophical Transactions of the Royal Society B. The papers in the collection examine light pollution’s effects in complex ecological systems such as insect communities, soil and grasslands.

The studies look at the growing prevalence of light pollution, while highlighting the cascading effects it has on the stability and functionality of ecosystems.

“While artificial light at night (ALAN) is crucial for the everyday life of humans… only a tiny fraction of reflected light is used for human vision, while the rest pollutes the environment. With an estimated annual average increase of 9.6% (estimated based on citizen science data), light pollution is one of the most pressing drivers of current global change, and it has become increasingly clear that the loss of the night has serious psychological, health, socio-economic and ecological consequences,” the authors wrote in the introduction.

Until now, studies on light pollution have mostly looked at its consequences for human health, as well as responses to it by particular species. Meanwhile, investigations of light pollution’s effects on highly interconnected communities of species have been lacking.

“Species do not exist in isolation but rather interact in numerous ways,” explained Dr. Myriam Hirt of iDiv and the University of Jena, who led the editing and compilation of the theme issue along with Dr. Remo Ryser, in the press release. “Our aim was to better understand how the brightening of the night sky affects entire ecosystems and the benefits they provide.”

For their studies, several researchers used the iDiv Ecotron — multiple chambers of controlled experimental ecosystems, called EcoUnits — to simulate and alter nighttime light conditions.

They found that artificial light had the ability to reach soil communities underground, affecting soil basal respiration and the efficiency of carbon use; alter plant traits like the hairiness of leaves, as well as lower plant diversity and biomass; affect the activity levels of invertebrates, which was associated with an increase in predation rates at night; and potentially homogenize the times when species are active, causing increased overlap and threatening species.

The studies also found that even low-level light pollution that is less bright than a full moon has wide-ranging effects on the physiological and behavioral responses of species. In addition, it has marked effects on more complex ecological networks and communities such as food webs.

“Their individual responses to artificial lighting and their relationships with one another determine the outcome for the entire ecological system. For instance, an activity shift of diurnal and crepuscular species into the night increases extinction risks in the entire community,” said Dr. Remo Ryser of the University of Jena and iDiv, who was one of the authors in the collection, in the press release.

Another study in the collection looked at the ways in which artificial light causes an indirect domino effect that can have consequences for humans. An example is ALAN’s effect on the behavior and abundance of a vector species like mosquitoes. The study demonstrates ALAN changes lead to alterations in the timing of important behaviors like mating, flight activity and host-seeking, which could have far-reaching consequences on vector-borne disease transmission, such as malaria.

“The benefits of artificial light during the night are undeniable, but its adverse effects should not be ignored,” Hirt said in the press release.

Another paper studied the ways in which various lighting strategies may lessen artificial light’s negative effects, though due to the nuanced approach needed when dealing with ALAN’s effect on different species, any mitigation procedures may not be applicable universally.

Darkness has become an increasingly rare commodity with the meteoric rise in artificial lighting, and this collection of studies puts the spotlight on how the proliferation of a widely used human invention has affected ecosystems as well as human health.

“By acknowledging the impact of this human-caused disturbance on species interactions and feedback loops, the special issue hopes to inspire future research and action that not only helps mitigate the harmful effects of light pollution, but fosters a sustainable coexistence between society’s needs and the natural environment,” the press release said.