In many parts of the world it is no longer really dark due to artificial light sources. To reduce the detrimental impact of this light pollution on biodiversity, scientists are now advocating the preservation of the few remaining dark areas. Based on the nocturnal activities of animals, a “dark infrastructure” is to be developed that connects these zones and provides wildlife with sufficient unlit refuges.
It is not only physical obstacles such as fences, roads and buildings that restrict animals in their natural behavior and cut up their habitats. Light can do this too, if there are too many artificial light sources in the wrong place at the wrong time. Light sources become a real barrier, especially for nocturnal animals that avoid light. Other animals, such as bats, birds or insects, are attracted or irritated by light sources and their nocturnal rhythm is disrupted. In both cases, the light affects the animals in their search for food or in their reproduction and thus also affects their survival.
Serious influence on different levels
The negative effects of light pollution are now considered to be a contributory factor in the worldwide decline of insects and the general decline in biodiversity. To protect the animals, Romain Sordello from the UMS PatriNat in Paris and his colleagues therefore propose a global network of protection zones to keep them dark at night. On the basis of previous studies, they have compiled known negative effects of light and then worked out solutions for establishing a so-called dark infrastructure.
As the researchers explain, the artificial light at night affects life at different levels – from the genes of individual individuals to entire ecosystems. For example, it lowers melatonin levels in many organisms, making it harder for them to synchronize day and night rhythms. “Great tits exposed to artificial light have an average of 49 percent less melatonin than the nocturnal birds, which leads to a change in the innate immune response,” explain Sordello and his colleagues. The mobility of animals can also be restricted: Birds, for example, which use natural light sources such as the moon, the Milky Way or other stars for orientation at night, can lose their spatial reference points due to the artificial light.
Dark sanctuaries for wildlife
But despite the known and suspected ecological effects, light pollution has not yet been an evaluation criterion, even in nature reserves. It has been shown that between 1992 and 2010 the number of dark areas in Europe decreased by 15 percent, including in protected areas. In order to counteract this development, future measures against light pollution should be based on the existing green infrastructures, according to the research team’s proposal. These are networks of sites designed and managed to contribute to biodiversity conservation and ecosystem stabilization.
According to the researchers, such networks should in future also include nighttime darkness as a protection criterion and ensure that a high degree of darkness is guaranteed to protect the animals. For the implementation of this dark infrastructure, Sordello and his colleagues describe a multi-step process: First, the light pollution is to be mapped in all its forms and dimensions. Then the dark retreats are identified, which the animals of the region need at least. In the third step, measures to maintain these low-light shelters are to be implemented. For example, in the French city of Douai, an acoustic survey of bat activity in the community area revealed dark infrastructure. These dark nons, which are important for bats, were included in the protection concept as a series of zones with varying degrees of darkness. The levels reflect the intensity of bat activity.
“In Germany, too, there is the potential to implement a dark infrastructure within the green and blue infrastructure with simple investigations and means,” explains co-author Franz Hölker from the Leibniz Institute of Freshwater Ecology and Inland Fisheries. In Germany there are already two certified star park islands, Pellworm and Spiekeroog, and with Fulda the first star city in Europe.
Source: Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB); Specialist article: Landscape and Urban Planning, doi: 10.1016/j.landurbplan.2021.104332